Scott Safety Gas Detection Reference Guide

TABLE OF CONTENTS INTRODUCTION 3 GAS CHARACTERISTICS Properties of a Gas Vapors and Aerosols Atmosphere Composition Fire Tetrahedron What is a Hazardous Atmosphere? Types of Gas, Vapor and Aerosol Hazards Toxicity Effects of Common Gases Upper and Lower Explosive Limits Limiting Exposure to Hazardous Atmospheres Combustible Gas Reference Guide Toxic Gas Reference Guide 4 5 6 7 8 9 10 11 12 13 14 24 SYSTEM 28 29 36 38 39 40 41 42 ARCHITECTURE AND APPLICATION Designing a Gas Detection System Industrial Hazards Common Hazards by Industry Fixed vs. Portable Detection Warnings, Alarms and Response Functions Ohm’s Law Relay Logic SENSOR TECHNOLOGY Catalytic Bead Sensors Infrared Sensors Electrochemical Sensors Photo Ionization Detector Metal Oxide Semiconductor Sensors Sensor Performance Factors Flame Detection 43 44 45 46 47 49 50 52 STANDARDS AND APPROVALS Hazardous Area Classifications Protection Methods and Standards NEMA Classifications/Ingress Protection ATEX CE Marking CSA International Underwriters Laboratories IECEx Factory Mutual Safety Integrity Level (SIL) Ratings 53 54 55 56 57 58 59 60 61 62 63 GLOSSARY OF GAS DETECTION TERMS Scott Safety Contact Information 64 81 INTRODUCTION As an industry leader in gas detection products, Scott Safety is committed to the life safety of workers in potentially dangerous industries such as petrochemical, pharmaceutical, wastewater treatment, and chemical processing. The ability to detect and analyze unseen threats through reliable gas detection products can and will save lives. The safety concerns with exposure to both toxic and combustible gases are the foundation of the need for reliable gas detection. Left undetected and unmonitored, hazardous gases pose grave threats to our health and safety. Exposure to toxic gases can cause a wide range of health effects including simple irritation, loss of consciousness, chronic illnesses, and even death. Combustible gases pose just as great a safety risk because of their potential to ignite and cause massive destruction. A well maintained gas detection program will combat the dangers and risks associated with hazardous conditions and help to safeguard life and property. Advanced monitoring techniques provide opportunities for: 3 • Early Warning of Hazardous Conditions • Intervention and Correction of the Causes of Hazardous Conditions • Time for Evacuation from Hazardous Conditions GAS CHARACTERISTICS The air we breathe every day is comprised of various gases. Though typically steady in composition, the quality of the air around us can change significantly when different toxic and combustible hazards are introduced into the immediate surrounding areas. From toxic* and combustible* gases to possibly harmful vapors* and aerosols,* the potential for a hazardous atmosphere* exists every day in work places across the world. Recognizing the properties and hazards of the gases that can enter and contaminate your workspaces is the first step in developing an effective gas detection program. Whether it’s recognizing the destructive potential of explosive combustible gases or safeguarding workers from the health hazards of toxic gas exposure, modern gas detection techniques are available to keep workers, equipment, and property safe. * Refer to the glossary for an explanation of this term 4 PROPERTIES OF A GAS 1. Gases will easily compress or expand based on the containment of the gas, temperature, pressure, and other factors. 2. Gases are comprised of a large number of weakly attracted molecules that can combine and react with other molecules and are in constant motion. Because of these properties, gas monitoring is very important. Gases will always fill the space they occupy until they can escape to another space. Gas leaks can occur suddenly and without warning causing a severe threat to life and property damage. 3. Gases will fill any size or shape container and are constantly in motion trying to escape the containment. 4. Many gases are either colorless or odorless and sometimes both. Q: If the ethane gas running through this piping system were to escape into your working atmosphere, would there be a need to detect its presence? Gas Temperature Boiling Point* Melting Point* Solid Liquid Solid and Liquid in equilibrium Energy Added * Refer to the glossary for an explanation of this term 5 Liquid and Gas in equilibrium A: Absolutely! Ethane gas is both odorless and colorless making its detection through simple observation nearly impossible. Additionally, ethane can displace oxygen causing a severe breathing hazard. Most importantly, ethane gas is a highly combustible gas that reaches an explosive point at only 3% v/v.* VAPORS AND AEROSOLS VAPORS Compounds with a boiling point below room temperature exist as a gas. Some compounds can exist as both a gas and a liquid at room temperature. The gaseous portion in equilibrium with the liquid is referred to as a vapor. For a combustible or flammable liquid, the vapor is what actually burns. Vapors travel along air currents and, when ignited, will flash back to their source. Most vapors are heavier than air and will accumulate in low lying areas. Some, like hydrogen, are lighter than air and will rise. Accumulated combustible vapors can reach their Lower Explosive Limit and present a serious ignition risk. Vapors and gases that have not yet reached their Lower Explosive Limit or have exceeded their Upper Explosive Limit still present a breathing risk as they can displace oxygen or be toxic in nature. 6 AEROSOLS An aerosol is a suspension of fine solid particles or liquid droplets in a gas. In effect, aerosols are a gaseous delivery system for contaminants. Smoke, smog, clouds, mists, and combustible emissions are examples of aerosols. Aerosols can cause adverse health effects when inhaled or absorbed through the skin. Aerosols can accumulate forming mists, smog, etc. These high concentrations can cause serious breathing and combustion risks. Both vapors and aerosols can create hazardous situations, especially in an enclosed space. Effective gas monitoring in areas where vapors or aerosols may be present can reduce the risks associated with toxic atmospheres and combustible concentrations. ATMOSPHERE COMPOSITION The Earth’s atmosphere is comprised of both permanent and variable gases. Permanent gases include the three most abundant gases: oxygen, nitrogen, and argon. These permanent gases remain the same concentration over time regardless of location in open environments. In confined spaces, these concentrations can vary widely. However, variable gases, such as methane and carbon dioxide, can vary over time and location. 7 Argon (Ar) 0.934% Nitrogen (N2) 78.084% Others (CO2, Ne, CH4, He, Kr, H2, Xe) < 1% Total Oxygen (O2) 20.9476% FIRE TETRAHEDRON To support combustion, four elements must be present: heat, oxygen, fuel source, and a chemical reaction. This is illustrated in the four-sided fire tetrahedron. Removal of any of the four elements will eliminate the flame. HOW DOES GAS MONITORING HELP IN THE PREVENTION OF FIRES? - Several (combustible) gases can provide the fuel source element of the fire tetrahedron. Monitoring levels can help identify potentially hazardous situations before they occur. - Many gases can lead to the increased likelihood of the chemical reaction element of the fire tetrahedron. Monitoring the presence of these gases can lead to an awareness of the potential for dangerous reactions to occur. - Monitoring of oxygen levels can help to identify an oxygen-rich environment that can lead to an increased likelihood of fire. 8 WHAT IS A HAZARDOUS ATMOSPHERE? A hazardous atmosphere is defined as one where one or more of the following conditions exist: - Flammable gas, vapor, or mist exists with a concentration of > 10% LEL* - Oxygen levels are < 19.5% or > 23.5% - Atmospheric concentration of any hazardous substance which could result in exposure in excess of the published dose per Occupational Safety and Health Administration (OSHA) regulations - Airborne combustible dust > 100% LEL - Any other atmospheric condition immediately dangerous to life or health (IDLH)* EXAMPLES OF THE CAUSES OF A HAZARDOUS ATMOSPHERE CONDITION: - O xygen is absorbed by the contents of a vessel or tank - O xygen is displaced by heavier-than-air gases - Leaking underground storage tanks and pipes - Decomposing organic matter or domestic waste - Piping system leak -Toxic substances being used in a confined space * Refer to the glossary for an explanation of this term 9 TYPES OF GAS, VAPOR AND AEROSOL HAZARDS Asphyxiants: • Simple • Chemical Causes suffocation by displacing oxygen. (examples: H2, CO) Causes suffocation by interfering with the blood’s ability to carry oxygen. (example: CO) Irritants/Corrosives Causes an inflammatory effect on tissue, especially in the respiratory tract, through contact with the compound. (examples: NH3 , Cl2 , O3 , SO2) Toxic Agents Poisonous to one or more organs such as the kidney (nephrotoxic) or liver (hepatotoxic). (examples: CS2, AsH3, CCl4) Carcinogens Causes cancer in humans and/or animals. (example: vinyl chloride, benzene) (CNS) Central Nervous System Depressants Disturb the proper functions of the CNS. (examples: benzene, acetone) Combustibles Liquids with a flash point between 100°F and 200°F. (example: acetic acid) Flammables Compounds with a flash point < 100°F or that form a flammable mixture with air at 13%v/v or less. (examples: ethyl alcohol, methane) 10 TOXICITY EFFECTS OF COMMON GASES OXYGEN CARBON MONOXIDE 5% 10% 15% 20% 25% 500 ppm x x 6-10% - Vomiting, loss of consciousness, death 10-14% - Abnormal fatigue 12-16% - Muscular coordination becomes impaired < 17% - Impaired judgment 19.5-23.5% - Safe level as per OSHA requirements > 23.5% - Oxygen enriched environment, high probability of fire HYDROGEN SULFIDE 100 ppm x x x 200 ppm 2000 ppm 2500 ppm x > 2500 ppm* - Fatal 1500 ppm - Mental confusion, possible loss of consciousness 400 ppm - Headache within 2 hours 200 ppm - Headache after several hours 25 ppm - Time weighted average exposure level ODORLESS CHLORINE 300 ppm 400 ppm x > 500 ppm - Fatal within 30-60 minutes 200 ppm - Headache and vomiting, potentially fatal 125 ppm - Temporary loss of smell 50 ppm- Eye and throat irritation 10 ppm - Time weighted average exposure level Odor threshold at 0.0005 ppm * Refer to the glossary for an explanation of this term 11 1000 ppm 1500 ppm x 500 ppm 10 ppm x x x 20 ppm 50 ppm 100 ppm x > 1000 ppm - Fatal 50 ppm - Potentially fatal after prolonged exposure 15 ppm - Throat irritation 3 ppm - Eye irritation 0.5 ppm - Time weighted average exposure level Odor threshold at 0.05 ppm 1000 ppm UPPER AND LOWER EXPLOSIVE LIMITS (UEL AND LEL) The Upper Explosive Limit, or UEL, is the point above which the concentration of gas mixture to atmosphere is too rich to burn. This is sometimes expressed as Upper Flammable Limit (UFL). The Lower Explosive Limit, or LEL, is the point below which the concentration of gas mixture to atmosphere is too lean to burn. This is sometimes expressed as Lower Flammable Limit (LFL). Any concentration between these limits may ignite or explode with little to no warning. Gas concentrations above the UEL are also extremely dangerous as they displace oxygen and must travel back through the explosive zone during ventilation efforts to reach safe limits. 100% 50% LEL 0% 60% LEL Too Lean To Burn 0% 90% LEL Increa LEL 100% ation ncentr as co sing g Explosion Zone UEL Too Rich To Burn To allow for adequate time to respond and recover from potentially hazardous and explosive atmospheres, CSA and ISA testing agencies require combustible sensors to respond to the exposure of a combustible gas in the following manner: • 50% LEL - Sensor must respond within 10 seconds (CSA* only) • 60% LEL - Sensor must respond within 12 seconds (ISA* only) • 90% LEL - Sensor must respond within 30 seconds (CSA and ISA) * Refer to the glossary for an explanation of this term 12 LIMITING EXPOSURE TO HAZARDOUS ATMOSPHERES TLV - THRESHOLD LIMIT VALUES Threshold limit values are established by the ACGIH (American Conference of Governmental Industrial Hygienists). They are the level to which a worker can be exposed to a chemical each day for a working lifetime without adverse health concerns. These limits are guidelines and not regulated by law. STEL - SHORT TERM EXPOSURE LIMIT Short term exposure limit is defined by ACGIH as the concentration to which workers can be exposed continuously for a short period of time without suffering from irritation, chronic or irreversible tissue damage, or narcosis of sufficient degree to increase the likelihood of accidental injury, impair self-rescue, or reduce work efficiency. PEL - PERMISSIBLE EXPOSURE LEVEL Permissible exposure levels are the maximum concentration a worker may be exposed to as defined by Occupational Safety and Health Administration (OSHA). PEL’s are defined in two ways, TWA and C. TWA - TIME WEIGHTED AVERAGE Time weighted average is an average value of exposure over the course of an eight hour work shift. C - CEILING LEVEL Ceiling level is an exposure limit that must never be exceeded. * The terms used and agencies identified here refer typically to the American market; however, the same general intent is made worldwide through each country’s governing body over occupational health and safety. 13 COMBUSTIBLE GAS REFERENCE GUIDE HOW TO USE THIS TABLE: Formula showing the atomic composition of the gas. American Chemical Society’s identification number for each gas. Useful when a gas has more than one name. Common name of combustible gases. Note that some gases can be known by multiple names. Combustible Gas n-Butanol 1-Butene 2-Butene Butyl Acetate n-Butyl Acrylate Ratio of the density of gas compared with ambient atmosphere. > 1.0 indicates the gas is heavier than air. Chemical Formula CH3(CH2)2CH3OH CH2=CHCH2CH3 CH3CH=CHCH3 CH3COOCH2(CH2)2CH3 CH2=CHCOOC4H9 CAS Number 71-36-3 106-98-9 107-01-7 123-86-4 141-32-2 Temperature at which the compound changes from a liquid to a gas. Temperature at which liquid emits a vapor to form an ignitable mixture in air. Temperature at which the gas is capable of self combustion. Relative Density Air = 1 2.55 1.95 1.94 4.01 4.41 % of atmosphere concentration when the gas reaches its Upper or Lower Explosive Limit. Ignition Boiling Flash Temp Point Point °C °C °C %LEL %UEL 359 449 325 370 268 116 -6.3 1 127 145 29 — Gas 22 38 1.7 1.6 1.6 1.3 1.2 12 10 10 7.5 8 NOTES: 14 All data is provided as a reference only. Refer to local authority such as NIOSH, ACGIH, OSHA, CCOHS, and others for current published values. —Indicates data has not been evaluated.  CAS Combustible Gas Chemical Formula Number Acetaldehyde Acetic Acid Acetic Anhydride Acetone Acetonitrile Acetyl Chloride Acetyl Fluoride Acetylacetone Acetylene Acetylpropyl Chloride Acrylaldehyde Acrylic Acid Acrylonitrile Acryloyl Chloride Allyl Acetate Allyl Alcohol Allyl Chloride Ammonia Amyl Alcohol Tert-Amyl Methyl Ether (TAME) Aniline Benzaldehyde Benzene Benzyl Chloride Bromoethane Butadiene Butane 15 CH3CHO CH3COOH (CH3CO)2O (CH3)2CO CH3CN CH3COCl CH3COF (CH3CH2)2CO CH=CH CH3CO(CH2)3Cl CH2=CHCHO CH2=CHCOOH CH2=CHCN CH2CHCOCl CH2=CHCH2OOCCH3 CH2=CHCH2CH CH2=CHCH2Cl NH3 CH3(CH2)3CH2OH (CH3)2C(OCH3)CH2CH3 C6H6NH2 C6H5CHO C 6H 6 C6H5CH2Cl CH3CH2Br CH2=CHCH=CH2 C4H10 75-07-0 64-19-7 108-24-7 67-64-1 75-05-8 75-36-5 557-99-3 96-22-0 74-86-2 5891-21-4 107-02-8 79-10-7 107-13-1 814-68-6 591-87-7 107-18-6 107-05-1 7664-41-7 71-41-0 994-05-8 62-53-3 100-52-7 71-43-2 100-44-7 74-96-4 106-99-0 106-97-8 Relative Ignition Boiling Flash Density Temp. Point Point Air = 1 °C °C °C 1.52 2.07 3.52 2 1.42 2.7 2.14 3 0.9 4.16 1.93 2.48 1.83 3.12 3.45 2 2.64 0.59 3.03 3.5 3.22 3.66 2.7 4.36 3.75 1.87 2.05 204 464 334 535 523 390 434 445 305 440 217 406 480 463 348 378 390 630 298 345 630 192 560 585 511 430 372 20 118 140 56 82 51 20 101.5 -84 71 53 139 77 72 103 96 45 -33 136 85 184 179 80 179 38 -4.5 -1 -38 40 49 < -20 2 -4 < -17 12 — 61 -18 56 -5 -8 13 21 -32 — 38 < -14 75 64 -11 60 < -20 -76 — % LEL % UEL 4 4 2 2.5 3 5 5.6 1.6 2.3 2 2.85 2.9 3.05 2.68 1.7 2.5 2.9 15 1.06 1.5 1.2 1.4 1.2 1.2 6.7 2 1.9 60 17 10 13 16 19 19.9 — 100 10.4 31.8 8 17 18 9.3 18 11.2 33.6 10.5 — 11 8.5 7.8 7.1 11.3 12 8.5  CAS Combustible Gas Chemical Formula Number n-Butanol 1-Butene 2-Butene Butyl Acetate n-Butyl Acrylate n-Butyl Bromide Tert-Butyl Methyl Ether Butylamine Butylmethacrylate n-Butylpropionate Butylraldhyde Carbon Disulfide Carbon Monoxide Carbonyl Sulfide Chlorobenzene 1-Chlorobutane 2-Chlorobutane Chloroethane 2-Chloroethanol Chloroethylene Chloromethane 1-Chloropropane 2-Chloropropane Chlorotrifluoroethylene Cresols Crotonaldehyde Cumene 16 CH3(CH2)2CH2OH CH2=CHCH2CH3 CH2CH=CHCH3 CH3COOCH2(CH2)2CH3 CH2=CHCOOC4H9 CH3(CH2)2CH2Br CH3OC(CH3)2 CH3(CH2)3NH2 CH2=C(CH3)COO(CH2)3CH3 C2H5COOC4H9 CH3CH2CH2CHO CS2 CO COS C6H5Cl CH3(CH2)2CH2Cl CH3CHClC2H5 CH3CH2Cl CH2ClCH2OH CH2=CHCl CH3Cl CH3CH2CH2Cl (CH3)2CHCl CF2=CFCl CH3C5H4OH CH3CH=CHCHO C6H5CH(CH3)2 71-36-3 106-98-9 107-01-7 123-86-4 141-32-2 109-65-9 1634-04-4 109-73-9 97-88-1 590-01-2 123-72-8 75-15-0 630-08-0 463-58-1 108-90-7 109-69-3 78-86-4 75-00-3 107-07-3 75-01-4 74-87-3 540-54-5 75-29-6 79-38-9 1319-77-3 123-73-9 98-82-8 Relative Ignition Boiling Flash Density Temp. Point Point Air = 1 °C °C °C 2.55 1.95 1.94 4.01 4.41 4.72 3.03 2.52 4.9 4.48 2.48 2.64 0.97 2.07 3.88 3.2 3.19 2.22 2.78 2.15 1.78 2.7 2.7 4.01 3.73 2.41 4.13 359 440 325 370 268 265 385 312 289 389 191 95 805 209 637 250 368 510 425 415 625 520 590 607 555 280 424 116 29 -6.3 — 1 Gas 127 22 145 38 102 13 55 -27 78 -12 160 53 145 40 75 -16 46 -30 -191 — -50 — 132 28 78 -12 68 < -18 12 — 129 55 -15 -78 -24 -24 37 -32 47 < -20 -28.4 Gas 191 81 102 13 152 31 % LEL % UEL 1.7 1.6 1.6 1.3 1.2 2.5 1.5 1.7 1 1.1 1.8 0.6 10.9 6.5 1.4 1.8 2.2 3.6 5 3.6 7.6 2.4 2.8 4.6 1.1 2.1 0.8 12 10 10 7.5 8 6.6 8.4 9.8 6.8 7.7 12.5 60 74 28.5 11 10 8.8 15.4 16 33 19 11.1 10.7 84.3 1.4 16 6.5  CAS Combustible Gas Chemical Formula Number Cyclobutane Cycloheptane Cyclohexane Cyclohexanol Cyclohexanone Cyclohexene Cyclohexylamine Cyclopentane Cyclopentene Cyclopropane Cyclopropyl Methyl Ketone p-Cymene trans-Decahydronaphthalene Decane Diacetone Alcohol Dibutyl Ether Dichlorobenzene 1,1-Dichlorethane 1,2-Dichlorethane Dichlorodiethylsilane Dichloroethylene 1,2-Dichloropropane Dicyclopentadiene Diethyl Ether Diethylamine Diethylcarbonate 1,1-Difluoroethylene 17 C 4H 8 C7H14 C6H12 C6H11OH C5H10CO C6H10 C6H11NH2 C5H10 C 5H 8 C 3H 6 C3H5COCH3 CH3(C6H4)CH(CH3)2 CH2(CH2)3CHCH(CH2)3CH2 C10H22 CH3COCH2C(CH3)2OH (CH3(CH2)3)2O C6H4Cl2 CH3CHCl2 CH2ClCH2Cl (C2H5)2SiCl2 ClCH=CHCl CH3CHClCH2Cl C10H12 (C2H5)2O (C2H5)2NH (C2H5CO)2O CH2=CF2 287-23-0 291-64-5 110-82-7 108-93-0 108-94-1 110-83-8 108-91-8 287-92-3 142-29-0 75-719-4 765-43-5 99-87-6 493-02-7 124-18-5 123-42-2 142-96-1 106-46-7 75-34-3 107-06-2 1719-53-5 540-59-0 78-87-5 77-73-6 60-29-7 109-86-7 105-58-8 75-38-7 Relative Ignition Boiling Flash Density Temp. Point Point Air = 1 °C °C °C 1.93 3.39 2.9 3.45 3.38 2.83 3.42 2.4 2.3 1.45 2.9 4.62 4.76 4.9 4 4.48 5.07 3.42 3.42 1.05 3.55 3.9 4.55 2.55 2.53 4.07 2.21 427 — 259 300 419 244 293 320 309 498 452 436 288 201 680 198 648 440 438 255 440 557 455 160 312 450 380 13 118.5 81 161 156 83 134 50 44 -33 114 176 185 173 166 141 179 57 84 128 37 96 170 34 55 126 -83 -63.9 < 10 -18 61 43 -17 32 -37 < -22 -94.4 15 47 54 46 58 25 86 -10 13 24 -10 15 36 -45 -23 24 — % LEL % UEL 1.8 1.1 1.3 1.2 1 1.2 1.6 1.4 1.48 2.4 1.7 0.7 0.7 0.7 1.8 0.9 2.2 5.6 6.2 3.4 9.7 3.4 0.8 1.9 1.7 1.4 3.9 11.1 6.7 8 11.1 9.4 7.8 9.4 9 — 10.4 — 6.5 4.9 5.6 6.9 8.5 9.2 16 16 — 12.8 14.5 6.3 36 10 11.7 25.1  CAS Combustible Gas Chemical Formula Number Diisobutyl Carbinol Diisobutylamine Diisopentyl Ether Diisopropyl Ether Diisopropylamine Dimethoxymethane Dimethyl Ether Dimethylaminopropiononitrile N,N-Dimethylformamide 1,4-Dioxane 1,3-Dioxolane Dipropylamine Epichlorohydrin Ethane Ethyl Mercaptan Ethanol 2-Ethoxyethanol 2-Ethoxyethylacetate Ethyl Acetate Ethyl Acetoacetate Ethyl Acrylate Ethyl Butyrate Ethyl Formate Ethyl Isobutyrate 18 ((CH3)2CHCH2)2CHOH ((CH3)2CHCH2)2NH (CH3)2CH(CH2)2O(CH2)2CH(CH3)2 ((CH3)2CH)2O ((CH3)2CH)2NH CH2(OCH3)2 (CH3)2O(CH3)2NH (CH3)2NHCH2CH2CN HCON(CH3)2 OCH2CH2OCH2CH2 OCH2CH2OCH2 (C3H7)2NH OCH2CHCH2Cl C 2H 6 C2H5SH C2H5OH CH3CH2OCH2CH2OH CH3COOCH2CH2OCH2CH3 CH3COOC2H5 CH3COCH2COOC2H5 CH2=CHCOOC2H5 CH3CH2CH2COOC2H5 HCOOC2H (CH3)2CHCOOC2H5 108-82-7 110-96-3 544-01-4 108-20-3 108-18-9 109-87-5 124-40-3 1738-25-6 68-12-2 123-91-1 646-06-0 142-84-7 106-89-8 74-84-0 75-08-1 64-17-5 110-80-5 111-15-9 141-78-6 141-97-9 140-88-5 105-54-4 109-94-4 97-62-1 Relative Ignition Boiling Flash Density Temp. Point Point Air = 1 °C °C °C 4.97 4.45 5.45 3.52 3.48 2.6 1.55 3.38 2.51 3.03 2.55 3.48 3.3 1.04 2.11 1.59 3.1 4.72 3.04 4.5 3.45 4 2.65 4 290 256 185 405 285 247 400 317 440 379 245 280 385 515 295 363 235 380 460 350 350 435 440 438 178 137 170 69 84 41 7 171 152 101 74 105 115 -87 35 78 135 156 77 181 100 120 52 112 75 26 44 -28 -20 -21 -18 50 58 11 -5 4 28 -135 < -20 12 40 47 -4 65 9 21 -20 10 % LEL % UEL 0.7 0.8 1.27 1 1.2 3 2.8 1.57 1.8 1.9 2.3 1.6 2.3 3 2.8 3.3 1.8 1.2 2.2 1 1.4 1.4 2.7 1.6 6.1 3.6 — 21 8.3 16.9 14.4 — 16 22.5 30.5 9.1 34.4 12.5 18 19 15.7 12.7 11 9.5 14 — 16.5 7.8  CAS Combustible Gas Chemical Formula Number Ethyl Methacrylate Ethyl Methyl Ether Ethyl Nitrate Ethylene Oxide Ethylamine Ethylbenzene Ethylcyclobutane Ethylcyclohexane Ethylcyclopentane Ethylene Ethylenediamine Formaldehyde Formic Acid 2-Furaldehyde Furan Furfuryl Alcohol Heptane Hexane Hexyl Alcohol Hydrogen Hydrogen Cyanide Hydrogen Sulfide Isobutane Isobutyl Alcohol Isobutyl Chloride Isobutylamine Isobutylene 19 CH2=C(CH3)COOC2H5 C2H5-O-CH3 C2H5ONO2 CH2CH2O C2H5NH2 C2H5-C6H5 CH2CH2CH2CH-C2H5 (CH2)5CH-C2H5 (CH2)4CH-C2H5 CH2=CH2 NH2CH2CH2NH2 HCHO HCOOH OCH=CHCH=CHCHO CH=CHCH=CHO OC(CH2OH)CHCHCH C7H16 C6H14 C6H13OH H2 HCN H 2S (CH3)2CHCH3 (CH3)2CHCH2OH (CH3)3CHCH2Cl (CH3)2CHCH2NH2 (CH3)2C=CH2 97-62-2 540-67-0 109-95-5 75-21-8 75-04-7 100-41-4 4806-61-5 1678-91-7 1640-89-7 74-85-1 107-15-3 50-00-0 64-18-6 98-01-1 110-00-9 98-00-0 142-82-5 110-54-3 111-27-3 1333-74-0 74-90-8 7783-06-4 75-28-5 78-83-1 513-36-0 78-81-9 115-11-7 Relative Ignition Boiling Flash Density Temp. Point Point Air = 1 °C °C °C 3.9 2.1 2.6 1.52 1.5 3.66 2.9 3.87 3.4 0.97 2.07 1.03 1.6 3.3 2.3 3.38 3.46 2.97 3.5 0.07 0.9 1.19 2 2.55 3.19 2.52 1.93 393 190 95 435 425 431 212 238 262 425 403 424 520 316 390 370 215 233 293 560 538 270 460 408 416 374 483 118 8 18 11 16.6 135 71 131 103 -104 118 -19 101 162 32 170 98 69 156 -253 26 -60 -12 108 68 64 -6.9 20 — -35 < -18 < -20 23 < -16 < 24 <5 — 34 — 42 60 < -20 61 -4 -21 63 — < -20 -82 Gas 28 < -14 -20 -80 % LEL % UEL 1.5 2 3 3 2.68 1 1.2 0.9 1.05 2.7 2.7 7 10 2.1 2.3 1.8 1.1 1.1 1.2 4 5.4 4 1.3 1.7 2 1.47 1.6 2.5 10.1 50 100 14 7.8 7.7 6.6 6.8 36 16.5 73 57 19.3 14.3 16.3 6.7 7.5 8 77 46 45.5 9.8 10.6 8.6 10.8 10  CAS Combustible Gas Chemical Formula Number Isobutylisobutyrate (CH3)2CHCOOH2CH(CH3)2 Isobutyraldhyde (CH3)2CHCHO Isodihydrolavandulyl Aldehyde C10H18O Isopropyl Acetate CH3COOCH(CH3)2 Isopropyl Alcohol (CH3)2CHOH Isopropyl Chloroacetate CICH2COOCH(CH3)2 Isopropyl Nitrate (CH3)2CHONO2 Isopropylamine (CH3)2CHNH2 Isovaleraldehyde (CH3)2CHCH2CHO Kerosene (Major Component of Jet Fuel) — Mesityl Oxide (CH3)2(CCHCOCH)3 Methacryloyl Chloride CH2CCH3COCl Methallyl Chloride CH2=C(CH3)CH2Cl Methane CH4 Methanol CH3OH 2-Methoxyethanol CH3OC2H4OH Methyl Acetate CH3COOCH3 Methyl Acetoacetate CH3COOCH2COCH3 Methyl Acrylate CH2=CHCOOCH3 Methyl Butyl Ketone (MBK) CH3CO(CH2)3CH3 Methyl Chlorformate CH3OOCC Methyl Ethyl Ketone (MEK) CH3COC2H5 Methyl Formate HCOOCH3 Methyl Isobutyl Carbinol (MIBC) (CH3)2CHCH2CHOHCH3 Methyl Isobutyl Ketone (MIBK) (CH3)2CHCH2COCH3 Methyl Mercaptan CH3SH Methyl Methacrylate CH2=C(CH3)COOCH3 20 97-85-8 78-84-2 35158-25-9 18-21-4 67-63-0 105-48-6 1712-64-7 75-31-0 590-86-3 8008-20-6 141-79-7 920-46-7 563-47-3 74-82-8 67-56-1 109-86-4 79-20-9 105-45-3 96-33-3 591-78-6 79-22-1 78-93-3 107-31-3 108-11-2 108-10-1 74-93-1 80-62-6 Relative Ignition Boiling Flash Density Temp. Point Point Air = 1 °C °C °C 4.93 2.48 5.31 3.51 2.07 4.71 0.86 2.03 2.97 4.5 3.78 3.6 3.12 0.55 1.11 2.63 2.56 4 3 3.46 3.3 2.48 2.07 3.5 3.45 1.6 3.45 424 176 188 467 425 426 175 340 207 210 306 510 478 537 386 285 502 280 415 533 475 404 450 334 475 340 430 145 63 189 85 83 149 101 33 90 150 129 95 71 -161 65 124 57 169 80 127 70 80 32 132 117 6 100 34 -22 41 4 12 42 11 < -24 -12 38 24 17 -16 -188 11 39 -10 62 -3 23 10 -9 -20 37 16 -18 10 % LEL % UEL 0.8 1.6 3.05 1.8 2 1.6 2 2.3 1.7 0.7 1.6 2.5 2.1 5 6 2.4 3.2 1.3 2.4 1.2 7.5 1.4 5 1.14 1.2 4.1 1.7 10.5 11 — 8.1 12.7 — 100 8.6 — 5 7.2 — 9.3 15 36 20.6 16 14.2 25 8 26 11.4 23 5.5 8 21 12.5  CAS Combustible Gas Chemical Formula Number α-Methyl Styrene Methylamine 2-Methylbutane 2-Methylbutanol 3-Methylbutanol 2-Methylbutene 2-Methylbutenyne Methylcyclohexane Methylcyclopentadiene Methylcyclopentane Methylenecyclobutane 2-Methylfuranl Methylisocyanate 2-Methylpentenal 2-Methylpyridine 3-Methylpyridine 4-Methylpyridine Methylthiophene Morpholine Naphthalene Nitrobenzene Nitroethane Nitromethane 1-Nitropropane Nonane Octane 1-Octanol 21 C6H5C(CH3)=CH2 CH3NH2 (CH3)2CHCH2CH3 CH3CH2C(OH)(CH3)2 (CH3)2CH(CH2)2OH (CH3)2C=CHCH3 HC=CC(CH3)CH2 CH3CH(CH2)4CH2 C 6H 6 CH3CH(CH2)4 C(=CH2)CH2CH2CH2 OC(CH3)CHCHCH CH3NCO CH3CH2CHC(CH3)COH NCH(CH3)CHCHCHCH NCHCH(CH3)CHCHCH NCHCHCH(CH3)CHCH SC(CH3)CHCHCHC OCH2CH2NHCH2CH2 C10H8 C6H5NO2 C2H5NO2 CH3NO2 CH3CH2CH2NO2 C9H20 C8H18 CH3(CH2)6CH2OH 98-83-9 74-89-5 78-78-4 75-84-4 123-51-3 513-35-9 78-80-8 108-87-2 26519-91-5 96-37-7 1120-56-5 534-22-5 624-83-9 623-69-9 109-06-8 108-99-6 108-89-4 554-14-3 110-91-8 91-20-3 98-95-3 79-24-3 75-52-5 108-03-2 111-84-2 111-65-9 111-87-5 Relative Ignition Boiling Flash Density Temp. Point Point Air = 1 °C °C °C 4.08 1 2.5 3.03 3.03 2.4 2.28 3.38 2.76 2.9 2.35 2.83 1.98 3.78 3.21 3.21 3.21 3.4 3 4.42 4.25 2.58 2.11 3.1 4.43 3.93 4.5 445 430 420 392 339 290 272 258 432 258 352 318 517 206 533 537 534 433 230 528 480 410 415 420 205 206 270 165 -6 30 102 130 35 32 101 — 72 41 63 37 137 128 144 145 113 129 218 211 114 102.2 131 151 126 196 40 -18 < -51 16 42 -53 -54 -4 < -18 < -10 <0 < -16 -7 30 27 43 43 -1 31 77 88 27 36 36 30 13 81 % LEL % UEL 0.9 4.2 1.3 1.4 1.3 1.3 1.4 1.16 1.3 1 1.25 1.4 5.3 1.46 1.2 1.4 1.1 1.3 1.8 0.9 1.7 3.4 7.3 2.2 0.7 0.8 0.9 6.6 20.7 8 10.2 10.5 6.6 — 6.7 7.6 8.4 8.6 9.7 26 — 8.6 8.1 7.8 6.5 15.2 5.9 40 — 63 — 5.6 6.5 7.4  CAS Combustible Gas Chemical Formula Number Paraldehyde Pentane-2,4-dione Pentane Pentyl Acetate Petroleum Petroleum Ether (Naptha) Phenol Piperylene Propane Propargyl Alcohol Propene Propionic Acid Propionic Aldehyde Propyl Acetate Propyl Alcohol Propylamine Propyne Pyridine R-1123 R-143a Styrene Tetrahydrofuran Tetrafluoroethylene 2,2,3,3,-Tetrafluoropropyl Methacrylate 2,2,3,3,-Tetrafluoro Propylacrylate Tetrahydrofurfuryl Alcohol Tetrahydrothiophene 22 OCH(CH3)OCH(CH3)OCH(CH3) CH3COCH2COCH3 C5H12 CH3COO-(CH2)4-CH3 — — C6H5OH CH2=CH-CH=CH-CH3 C 3H 8 HC=CCH2OH CH2=CHCH3 CH3CH2COOH C2H5CHO CH3COOCH2CH2CH3 CH3CH2CH2OH CH3(CH2)2NH2 CH3C=CH C 5H 5N CF2=CFH CF3CH3 C6H5CH=CH2 CH2(CH2)2CH2O CF2=CF2 CH2=C(CH2)COOCH2CF2CF2H CH2=CHCOOCH2CF2CF2H OCH2CH2CH2CHCH2OH CH2(CH2)2CH2S 123-63-7 123-54-6 109-66-0 628-63-7 — 8030-30-6 108-95-2 504-60-9 74-98-6 107-19-7 115-07-1 79-09-4 123-38-6 109-60-4 71-23-8 107-10-8 74-99-7 110-86-1 359-11-5 420-46-2 100-42-5 109-99-9 116-14-3 45102-52-1 7383-71-3 97-99-4 110-01-0 Relative Ignition Boiling Flash Density Temp. Point Point Air = 1 °C °C °C 4.56 3.5 2.48 4.48 2.8 2.5 3.24 2.34 1.56 1.89 1.5 2.55 2 3.6 2.07 2.04 1.38 2.73 1.26 1.30 3.6 2.49 3.4 6.9 6.41 3.52 3.04 235 340 258 360 560 290 595 361 470 346 455 435 188 430 405 318 — 550 319 714 490 224 255 389 357 280 200 123 140 36 147 — 35-80 182 42 -42 114 -48 141 46 102 97 48 -23.2 115 -57 -47.6 145 64 -76.6 124 132 178 119 27 34 -40 25 < -20 < -18 75 < -31 -104 33 -108 52 < -26 10 22 -37 -51 17 — — 30 -20 — 46 45 70 13 % LEL % UEL 1.3 1.7 1.4 1 1.2 0.9 1.3 1.2 2.1 2.4 2 2.1 2 1.7 2.2 2 1.7 1.7 15.3 6.8 1.1 1.5 10 1.9 2.4 1.5 1.1 17 — 7.8 7.1 8 6 9.5 9.4 9.5 — 11 12 — 8 17.5 10.4 16.8 12 27 17.6 8 12.4 59 — — 9.7 12.3  CAS Combustible Gas Chemical Formula Number N,N,N’,N’,-Tetramethyldiaminomethane Thiophene Toluene Triethylamine Trifluoroethanol 3,3,3-Trifluoropropene Trimethylamine 1,2,3-Trimethylbenzene 1,3,5-Trimethylbenzene 2,2,4-Trimethylpentane 1,3,5-Trioxane Turpentine Vinyl Acetate Vinyl Cyclohexane Vinylidene Chloride 2-Vinylpyridine 4-Vinylpyridine Xylene 23 (CH3)2NCH2N(CH3)2 CH=CHCH=CHS C6H5CH3 (C2H5)3N CF3CH2OH CF3CH=CH2 (CH3)3N CHCHCHC(CH3)C(CH3)C(CH3) CHC(CH3)CHC(CH3)CHC(CH3) (CH3)2CHCH2C(CH3)3 OCH2OCH2OCH2 ~C10H16 CH3COOCH=CH2 CH2CHC6H9 CH2=CCl2 NC(CH2=CH)CHCHCHCH NCHCHC(CH2=CH)CHCH C6H4(CH3)2 51-80-9 110-02-1 108-88-3 121-44-8 75-89-8 677-21-4 75-50-3 526-73-8 108-67-8 540-84-1 110-88-3 — 108-05-4 100-40-3 75-35-4 100-69-6 100-43-6 1330-20-7 Relative Ignition Boiling Flash Density Temp. Point Point Air = 1 °C °C °C 3.5 2.9 3.2 1.2 1.38 3.3 1.6 4.15 4.15 3.9 3.11 1.01 3 3.72 3.4 3.62 3.62 3.66 180 395 535 294 463 490 190 470 499 411 410 254 425 257 440 482 501 464 85 84 111 89 77 -16 3 175 163 98 115 149 72 126 30 79 62 144 < -13 -9 4 -7 30 — -6 51 44 -12 45 35 -8 15 -18 35 43 30 % LEL % UEL 1.61 1.5 1.1 1.2 8.4 4.7 2 0.8 0.8 1 3.2 0.8 2.6 0.8 7.3 1.2 1.1 1 — 12.5 7.1 8 28.8 13.5 12 7 7.3 6 29 — 13.4 — 16 — — 7 TOXIC GAS REFERENCE GUIDE HOW TO USE THIS TABLE: Common name of toxic gases. Note that some gases can be known by multiple names. American Chemical Society’s identification number for each gas. Useful when a gas has more than one name. Threshold limit value as established by the ACGIH. Formula showing the atomic composition of the gas. Ratio of the density of gas compared with ambient atmosphere. > 1.0 indicates the gas is heavier than air. Chemical Formula CAS Number Relative Density Air = 1 BF3 Br2 CO2 CS2 CO 7637-07-2 7726-95-6 124-38-9 75-15-0 630-08-0 Toxic Gas Boron Trifluoride Bromine Carbon Dioxide Carbon Disulfide Carbon Monoxide 2.18 0.6 1.5 2.6 1.0 Permissible exposure limit as established by OSHA. Short term exposure limit as established by EH40/2005. TLV (PPM) 1* 0.10 5,000 10 25 STEL (PPM) — 0.20 30,000 — — The lowest airborne concentration that can be detected by smell. Immediately dangerous to life or health level of exposure. PEL (PPM) 1 (C) 0.10 5,000 20 50 IDLH (PPM) 25 3 40,000 500 1200 Odor Threshold (PPM) 1.5 0.066 74,000 0.096 100,000 NOTES: 24 All data is provided as a reference only. Refer to local authority such as NIOSH, ACGIH, OSHA, CCOHS, and others for current published values. — Indicates data has not been evaluated. “C” Indicates ceiling level value.  Toxic Gas Chemical Formula CAS Number Relative Density Air = 1 TLV (PPM) STEL (PPM) PEL (PPM) IDLH (PPM) Odor Threshold (PPM) Ammonia NH3 7664-41-7 0.6 25 35 50 300 5.75 Arsine AsH3 7784-24-1 2.7 0.05 — 0.05 3 < 1.0 Benzene C 6H 6 71-43-2 0.88 0.5 2.5 — 500 8.65 Boron Trichloride BCl3 10294-34-5 4.1 — — — — — Boron Triflouride BF3 7637-07-2 2.18 1 — 1 (C) 25 1.5 Bromine Br2 7726-95-6 0.6 0.10 0.20 0.10 3 0.066 Carbon Dioxide CO2 124-38-9 1.5 5,000 30,000 5,000 40,000 74,000 Carbon Disulfide CS2 75-15-0 2.6 10 — 20 500 — Carbon Monoxide CO 630-08-0 1.0 25 — 50 1200 100,000 Carbonyl Sulfide COS 463-58-1 2.1 — — — 2 — Chlorine Cl2 7782-50-5 2.5 0.5 1.0 1.0 10 0.05 Chlorine Dioxide ClO2 10049-04-4 2.3 0.1 0.3 0.1 5 9.24 Cyanogen Chloride CNCl 506-77-4 2.1 0.3 0.3 0.3 — 0.976 Diborane B 2H 6 19287-45-7 2.9 0.10 — 0.10 15 1.8 - 3.5 Dichlorosilane SiH4Cl2 4109-96-0 3.5 — — — — — Dimethyl Amine (DMA) C2H7N 124-40-3 0.7 5 6 10 500 0.081 Disilane Si2H6 1590-87-0 2.1 — — — — — Ethylene Oxide CH2OCH2 75-21-8 1.5 1.0 — 1.0 800 851 25  Toxic Gas Chemical Formula CAS Number Relative Density Air = 1 TLV (PPM) STEL (PPM) PEL (PPM) IDLH (PPM) Odor Threshold (PPM) Fluorine F2 7782-41-4 1.3 1.0 2.0 0.1 25 0.126 Formaldehyde CH2O — — 0.3 — — 20 0.871 Germane GeH4 7782-65-2 2.7 0.2 — — — — Hydrazine N 2H 4 302-01-2 1.1 0.0 — 1.0 50 3.6 Hydrogen Bromide HBr 10035-10-6 2.8 — 3 (C) 3.00 3 1.99 Hydrogen Chloride HCl 7647-01-0 1.3 — 5 (C) 5 (C) 50 0.77 Hydrogen Cyanide HCN 74-90-8 0.9 — 4.7 (C) 10.00 50 0.603 Hydrogen Fluoride HF 7664-39-3 0.7 3 3 (C) 3 30 0.036 Hydrogen Iodide HI 10034-85-2 4.5 — — — — — Hydrogen Peroxide H2O2 7722-84-1 1.2 1.0 — 1.00 75 — Hydrogen Selenide H2Se 7783-07-5 2.8 0.05 — 0.05 100 0.3 Hydrogen Sulfide H 2S 7783-06-4 1.2 1 5 20 (C) 100 0.0005 Methanol CH3OH 67-56-1 0.8 200 250 200 25,000 — Methyl Iodide CH3I 74-88-4 2.9 2 2 5 100 — Methyl Mercaptan CH3SH 74-93-1 0.9 — — 10 (C) 150 0.001 Monomethyl CH3(NH)NH2 60-34-4 1.6 0.01 — 0.2 50 1.71 Nitric Acid HNO3 7697-37-2 1.4 2 4 2 25 0.267 Nitric Oxide NO 10102-43-9 1.0 25.0 — 25.00 100 — 26  Toxic Gas Chemical Formula CAS Number Nitrogen Dioxide NO2 Nitrogen Trifluoride NF3 Relative Density Air = 1 TLV (PPM) STEL (PPM) PEL (PPM) IDLH (PPM) Odor Threshold (PPM) 10102-44-0 2.6 3 5 5 20 0.186 7783-54-2 2.4 10 — 10 1000 — n-Butyl Amine CH3(CH2)2CH2-NH2 109-73-9 0.74 5 (C) — 5 (C) 300 0.053 Oxygen Deficiency O2 — 0.9 — — <19.5% <18% — Oxygen Enrichment O2 — 0.9 — — >23.5% — — Ozone O3 10028-15-6 1.7 0.1 — 0.10 5 0.051 Phosgene COCl2 75-44-5 3.4 0.1 — 0.1 2 0.55 Phosphine PH3 7803-51-2 1.2 0.3 1.0 0.30 50 0.14 Propylene Oxide C 3H 6O 75-56-9 1.6 2 — 100 400 33.1 Silane SiH4 7803-62-5 1.3 5 — — — — Silicon Tetrafluoride SiF4 7783-60-0 — — — — 3 — Stibine SbH3 7803-52-3 2.26 0.1 — 0.1 5 — Sulfur Dioxide SO2 7446-09-5 2.3 — 0.25 5 100 0.708 Styrene Tetraethyl Orthosilicate (TEOS) C6H5CH=CH2 100-24-5 3.6 20.0 40 10.00 700 — (C2H5O)4Si 78-10-4 7.2 100 10 10 700 — Triethylamine (TEA) C6H16N 121-44-8 1.2 5 4 — 200 0.309 75-01-4 2.0 1 — — Carcinogen 35.5 Vinyl Chloride (VCM) CH2=CHCl 27 SYSTEM ARCHITECTURE AND APPLICATION The most common applications in hazardous atmosphere monitoring occur with the use of mounted fixed gas detection systems. These systems are set in place to provide continuous monitoring in areas where leaks, ruptures, or releases of hazardous gases are likely to occur whether indoor or outdoor. THERE ARE SEVERAL FACTORS TO CONSIDER WHEN INSTALLING A FIXED DETECTION SYSTEM. AMONG THE MORE BASIC ONES: How many monitors are needed to provide adequate protection? What areas will be monitored locally and which will be monitored from a remote location? What types of safety measures can be activated should a hazardous situation occur? Will the environment the sensors are located in affect performance? Is there sufficient oxygen for the sensor type to respond? Is the target gas heavier or lighter than air? Where are the receptor* and release* points in the process? Is the environment the sensor will be installed in subjected to high traffic or wash downs? What is the area classification of the location for installation? Are there other gases present that may react or cause a cross interference with target gases? * Refer to the glossary for an explanation of this term 28 DESIGNING A GAS DETECTION SYSTEM A fixed gas detection system is a highly customizable application comprised of any number of combinations of point detectors, networked monitoring, automatic response functions, or audible and visual alarms. Each process* that requires gas detection must be carefully evaluated to identify and understand the potential risk factors and what the best potential monitoring and response functions are to reduce those risks. Scott Safety will work with customers to help identify the risks and provide design solutions that maximize value and safety. Five areas of consideration can help with a system design. Sometimes, a solution is as simple as a single point of detection. More frequently, however, careful evaluation of an overall process yields an opportunity to significantly reduce the risks and hazards of a plant process. These areas are: 1. UNDERSTAND THE APPLICATION 2. IDENTIFY POTENTIAL DANGER POINTS 3. ESTABLISH DESIGN GOALS 4. DETERMINE GAS CHARACTERISTICS 5. PROFILE THE FACILITY * Refer to the glossary for an explanation of this term 29 UNDERSTAND THE APPLICATION Legal requirements, local and federal regulations, fire and building codes, and industry safety standards all play a significant role in determining the applicability of minimum safety requirements when monitoring for toxic and combustible hazards in the workplace. Certain requirements for gas monitoring are based on the physical design and layout of plant processes. Semiconductor facilities, wastewater treatment plants, and natural gas delivery systems all have their own unique requirements for monitoring and automatic response functions to alarms. Physical factors to consider when designing a system include indoor/outdoor use, amount and direction of ventilation, enclosed spaces, possible ignition sources, power availability for installation, receptor points, release points, and whether exposure to other toxic substances may occur. Workers should only be subjected to certain limits of different types of contaminants. These restricted limits are defined as STEL, TWA, IDLH, and ceiling limits among other factors. Agencies such as NIOSH, ACGIH, OSHA, CCOHS, IOHA* and others set and recommend these levels to protect individuals from exposures to harmful levels of hazardous substances. Another major consideration in understanding the application is to know the characteristics of the monitored hazardous substances. Gases can be both toxic and combustible; however, the importance of monitoring is to reduce the risk from whichever characteristic is more likely to occur. Carbon monoxide, for example, is a combustible hazard when it reaches a concentration of 12.8% LEL or 128,000 ppm. However the established STEL is 400 ppm and becomes IDLH at only 1200 ppm. In areas where workers can be exposed to carbon monoxide, the appropriate application is to monitor for toxic levels. * Refer to the glossary for an explanation of this term 30 IDENTIFY POTENTIAL DANGER POINTS Danger points are identified in one of two ways, release points and receptor points. RELEASE POINT - Location where hazardous gases can potentially be released, also referred to as the source RECEPTOR POINT - Location where hazardous gases cause a threat to personnel, property, or facilities In general, all areas of a facility where gases are transported, stored, processed, delivered, or utilized are danger points. However, by focusing on the points where the occurrence of gas is most likely to occur, or most likely to pose a danger to people, property, or equipment, a balance of safety and cost can be considered. The areas between release points and receptor points typically have the highest need for gas detection. Scott Safety can assist with identifying the potentially dangerous release points and the most likely receptor points. COMMON RELEASE POINTS COMMON RECEPTOR POINTS • Seals, flanges, gaskets, piping manifolds, and valve stems • Analyzer shelters • Weld-beads • Liquid and gas storage areas • Battery rooms • Sumps, sewers, wastewater treatment areas 31 Space Between Release and Receptor Points = The Need for Gas Detection and Monitoring • Confined spaces • Maintenance areas • Ventilation distribution points • Personnel facilities • Pump rooms • Gas transportation routes • Storage areas • Semiconductor processing areas • Fresh air intakes ESTABLISH DESIGN GOALS When designing a gas detection system to meet the needs of your process or facility, planners will need to plan the goals, or response functions, of the gas detectors when warning and alarm conditions occur. RESPONSE FUNCTIONS KEY CONSIDERATIONS NOTIFICATION AND ANNUNCIATION HUMAN RESPONSE TIME OF AN ALARM EVENT Warnings and alarms are projected through the use of lights, bells, whistles, buzzers, horns, sirens, or any other method to get the attention of personnel and responders. Will the detectors be continuously manned or will automatic functions be required? What are the consequences of not responding quickly? VENTILATION CONTROL REDUNDANCY OF DETECTION EQUIPMENT Warnings and alarms may trigger automatic ventilation actions to occur. In some instances, ventilation may be secured to control the spread of a gas. Other times, ventilation may be increased to aid in the purging of dangerous gases. What are the costs associated with a false alarm? What zone/voting configurations are required? PROCESS SHUTDOWN Warnings and alarms may trigger both automatic and human initiated process shutdowns ranging from closing flow control valves and manifolds to securing power to equipment to isolating areas. EVACUATION AND EMERGENCY RESPONSE Warnings and alarms may trigger human initiated evacuations and automatic notification to emergency responders. * Refer to the glossary for an explanation of this term 32 MARGIN OF SAFETY What are the reaction by-products that could occur if one gas mixes with another? What effects will temperature, humidity, high pressure releases, vapor clouds, and oxygen displacement have on process monitoring? LEGAL AND REGULATORY REQUIREMENTS Are all the requirements of local laws, codes, SIL, and other industry standards being met? DETERMINE GAS CHARACTERISTICS Simply knowing whether a particular gas needs to be monitored at toxic or combustible levels is not enough. Other factors play just as large a role in determining the optimum locations for points of detection. VAPOR DENSITY* Heavier than air gases and vapors tend to sink and accumulate in lower lying areas. They typically will not disperse quickly and may displace oxygen. Sensors for these gases and vapors should be located approximately 18–24" (46–61 cm) above floor level. Lighter than air gases will tend to rise in the atmosphere and sensors should be placed above the release point. It is not uncommon for these sensors to be placed at or near the ceilings of indoor facilities. GAS RELEASE TEMPERATURES Temperature and vapor density have an inversely proportionate relationship; that is, as temperature increases the vapor density will decrease and as temperature cools, vapor density will increase. This is important to consider as some heated or cooled gases and vapors will not initially rise or fall as they would if they were at ambient temperatures. VENTILATION AND AIR CURRENTS Lighter than air gases may disperse and travel across ventilation and air currents quicker than they would otherwise rise. Consideration may be given to placing sensors near exhaust paths or exhaust ducts to account for this air flow. RATE OF EVAPORATION Vapors that evaporate slowly over standing liquids tend to be dense so sensors should be placed closer to liquids or potential spill locations to account for this. Vapors with a higher rate of evaporation can act similar to lighter than air gases and be taken with air currents. HIGH PRESSURE GASES AND VAPORS Gases under pressure can tend to emit from a release point as a gas jet. If the physical structure of the release point is such that the jet’s path is predictable, sensors should be placed directly in the path of the jet. If the release point does not provide a predictable path, multiple sensors should be utilized around the release point. Gas jets may produce heavy aerosols. Lighter than air vapors and gases will not immediately rise when released under pressure as part of these aerosols. * Refer to the glossary for an explanation of this term 33 PROFILE THE FACILITY The last consideration that needs to be made is to identify the physical, environmental, and air flow constraints that are in place at the facility where the gas detectors and sensors will be installed. These constraints will be unique to each facility and proper foresight can prevent costly repairs, relocation of equipment, and help to minimize false alarms. USE IN A HAZARDOUS LOCATION Not all gas detection equipment is designed equally for use in classified areas. Note the highest zone or division the classified area is and ensure the detection equipment selected is suitable for use in these areas. INDOOR/OUTDOOR USE Perhaps the simplest of considerations, and most important to the basic design of a fixed gas detection system is whether the monitors are to be used indoors or outdoors. Outdoor applications present challenges in the number of detectors to be used because gases will rapidly disperse into the atmosphere. Open path* technology can help to lower the number of sensors and increase their effective range, but they will not work for all gases and must have a clear line of sight between the sensor and receiver. Indoor applications that confine a gas release may require lower warning and alarm settings as the concentration of released gas will rise rapidly in an enclosed environment. PHYSICAL INTERFERENCE Gas releases will move more rapidly over smooth surfaces such as floors, concrete, water, and grass. Areas where physical barriers such as cabinets, buildings, lockers, piping, and storage tanks exist will change the flow of a released gas, and may confine the gas. Sensors mounted in low lying areas should be kept clear of transportation routes and protected from areas where routine cleaning or precipitation would splash and possibly effect the ability of sensors to function properly. AIR FLOW Prevailing winds and humidity levels make a big difference in how the flow of a released gas will disperse in outdoor applications. Gas dispersion models can be used to predict likely release paths and help target the best locations for gas detectors. Indoor applications are effected by the volume of air flow in ventilated areas and whether enclosed areas have exhaust lines. Smoke studies, where a puff of visible smoke is released, can be done to follow the air current and predict the path of a released gas. * Refer to the glossary for an explanation of this term 34 PROFILE THE FACILITY The last consideration that needs to be made is to identify the physical, environmental, and air flow constraints that are in place at the facility where the gas detectors and sensors will be installed. These constraints will be unique to each facility and proper foresight can prevent costly repairs, relocation of equipment, and help to minimize false alarms. ENVIRONMENTAL CONDITIONS All gas detectors have temperature restrictions that effect the environment in which they can be used. Sensor technologies vary in performance from arid to high humidity conditions. Weather shields and other accessories are usually available to help protect gas detection equipment. Filters may help to prevent dust and particulates from interfering with sensor performance. ACCESSIBILITY OF THE MONITOR AND SENSOR When mounting a gas detector and the sensor, use foresight and planning to anticipate needing to perform routine calibrations* and sensor replacements. Mounting a sensor in a remote area that is difficult to access can cause problems when routine maintenance needs arise. Similarly, when facility changes and expansions are done, an evaluation should be conducted to verify the mounted gas detectors are still performing as expected and will still be able to be accessed as needed. Sensors should never be painted over. WIRING AND INSTALLATION Wiring and installation costs can significantly impact the cost of a well designed gas detection system. Proper planning should occur prior to installation to verify the infrastructure is in place to provide the proper power to each component and account for voltage loss that will occur over long cable runs. Mounting of transmitters* should be done in such a way that meets all applicable building codes and minimizes the effects of any residual vibration from nearby equipment. EMI* AND RFI* Electromagnetic and radio frequency interference are legitimate concerns when installing gas detectors. Interference and electrical noise spikes can generate false alarms in equipment. Verify all wiring is properly shielded and encased in suitable conduit. Detectors should always be grounded. Wireless surveys should be done to analyze the suitability of using wireless detectors and sensor heads* as the technology emerges. * Refer to the glossary for an explanation of this term 35 INDUSTRIAL HAZARDS Combustible hazards Toxic hazards Hazardous gas monitoring has a place in most industries worldwide for the safety of personnel, property, and facilities. Fixed and portable detection units can mean the difference in saving lives and preventing costly incidents. Whether it’s handling, manufacturing, transporting, processing, or treating potentially hazardous substances, Scott Safety can help customers determine what products can best fit their needs for each necessary application. PETROCHEMICAL, OIL, AND GAS PHARMACEUTICAL WASTEWATER TREATMENT FACILITIES Potential activities requiring gas detection: Potential activities requiring gas detection: Potential activities requiring gas detection: Refining operations Chemical processing Standing water operations On/off shore drilling Storage facilities Enclosed tanks and sewers Compressor stations Volatile emissions Chemical processing Pump stations Notable gases of interest: Notable gases of interest: Notable gases of interest: Hydrocarbon gases - Ethane, Methane VOCs*, Methane VOCs*, Methane Carbon Monoxide, Hydrogen Sulfide, Hydrogen Fluoride Solvents, Silicones, Oxygen, Ethylene Oxide Sulfur Dioxide, Chlorine, Hydrogen Sulfide, Ammonia, Ozone, Oxygen (depletion) * Refer to the glossary for an explanation of this term 36 INDUSTRIAL HAZARDS SEMICONDUCTOR FABRICATION GENERAL INDUSTRY/ CHEMICAL PROCESSES FOOD AND BEVERAGE Potential activities requiring gas detection: Potential activities requiring gas detection: Potential activities requiring gas detection: Chemical vapor deposition Gas delivery and transportation Refrigeration Gas storage Pump and piping systems Sanitizing processes Reacting agents and chemical drying processes Laboratory operations Notable gases of interest: Notable gases of interest: Notable gases of interest: Hydrogen Methane, Flammable Vapors, VOCs Carbon Monoxide Silane, Carbon Monoxide, Arsine Hydrogen Sulfide, Hydrogen Chloride, Carbon Monoxide, Oxygen (deficiency), Chlorine, Sulfur Dioxide, Hydrogen Chloride Carbon Dioxide, Ammonia, Chlorine, Oxygen (deficiency), Sulfur Dioxide * Refer to the glossary for an explanation of this term 37 Combustible hazards Toxic hazards Ammonia (NH3) Carbon Dioxide (CO2) Carbon Monoxide (CO) Chlorine (Cl2) Combustible Gases Hydrogen (H2) Hydrogen Chloride (HCl) Hydrogen Cyanide (HCN) Hydrogen Sulfide (H2S) Nitrogen Dioxide (NO2) Nitric Oxide (NO) O2 Enrichment/Deficient Phosphine (PH3) Sulfur Dioxide (SO2) Volatile Organic Compounds (VOC)* * Refer to the glossary for an explanation of this term 38 lan cW or ks W a T ter re a tm en t bli Pu rP we Po ar ma ce ut ts ica l r pe Pa Ph d lp Pu PO G an ing ipp Sh C hem Pla ica nt l s Co ns tru cti on Ele U ctr tili ica tie l s Fir e S HA er ZM vic AT e/ Fo o Be d ve an ra d ge Se rvi Ga ce sU tili tie s St ee l ion iat Av Ag ric ult ur e COMMON HAZARDS BY INDUSTRY FIXED VS. PORTABLE DETECTION FIXED GAS DETECTION refers to a permanently mounted sensor or system of sensors. At a minimum, the sensors are connected to a transmitter or controller*, and commonly are connected to a network consisting of multiple points of detection, alerts, alarms, and response functions. Fixed gas detection is used for continuous monitoring of gas concentrations to protect people, facilities, and equipment. It provides around the clock monitoring in local or remote locations and does not require a constant human monitor or response. ADVANTAGES 1. Continuous, real-time monitoring 2. Customizable automatic response functions 3. Easy to maintain routine maintenance and calibration LIMITATIONS 1. Costs more than portable 2. Requires independent reliable power source 3. Not easily relocated when process needs change * Refer to the glossary for an explanation of this term 39 PORTABLE GAS DETECTION refers to a handheld system of sensors that provides protection for an individual user. Alarm functions in the form of visual, audible, and vibratory alerts notify users when detection of a hazardous situation has occurred and requires a human response. Portable units are typically used in confined space entries, areas where fixed gas detection is not available or providing continuous monitoring, or to verify an atmosphere is not hazardous when servicing a fixed gas detection system. ADVANTAGES 1. Costs less than fixed systems 2. Can be taken anywhere a user can go 3. Typically battery powered, not tied to a power source LIMITATIONS 1. Does not provide automatic response functions 2. Users must be properly trained to ensure proper usage WARNINGS, ALARMS AND RESPONSE FUNCTIONS Through the use of relays and customizable alarm point settings, users are able to configure their systems and transmitters to respond to changing hazardous conditions. Relays may be activated to perform any number of functions including activating visual and audible alarms, closing electronic isolation valves, and starting or stopping exhaust fans. This type of automatic system response can save lives and alert workers to hazardous situations. Most systems also have an option for a remote alarm reset. This enables users to acknowledge alarm conditions from a remote (safe) location. Automatic data logging of significant events such as calibrations, alarms, and power interruptions can usually aid users when performing troubleshooting or historical trend analysis. 40 OHM’S LAW One of the challenges that can go into designing an effective fixed gas detection system is understanding the maximum cable lengths that can be utilized for remote detector heads, alarm systems, remotely mounted transmitters, etc. Voltages can be lost over long lengths of cable. Proper planning and understanding the relationships in an electrical system will help the design and effectivity of the fixed gas detection system. E*I I2 * R Ohm’s Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. P - This is the total power generated in a circuit. It is the product of current and voltage, measured in watts. E - This is the difference in electrical potential between two points of a circuit, measured in volts. Volts are the muscle to move current. I - This is the current, or what flows on a wire, measured in amps. E2 / R P*R R - This the resistance of the circuit, or what determines how much electricity can flow in a circuit. As resistance increases, current flow becomes less and vice versa. Measured in ohms. *O  NE VOLT OF ELECTRICITY WILL CARRY ONE AMP OF CURRENT THROUGH ONE OHM OF RESISTANCE TO PRODUCE ONE WATT OF POWER. Notes • W ire sizes and materials will vary from manufacturer to manufacturer resulting in different resistance values. Always consult manufacturer’s technical specifications for accurate resistance values. • The voltage output from a power source will not be the voltage received at the other end of the wire run. Voltage loss will occur over the length of a wire run. • 1 amp = 1000 mA (milliamps), 1000 volts = 1 kV (kilovolt) 41 E/R P/E P I Watts Amps Volts Ohms E R P /I P/R P/ I2 E2 / P I*R E/I RELAY LOGIC A key feature of most fixed point gas detection systems are standard and optional relays. Relays open or close contacts to complete or break an electrical circuit when user configured set points have been met. Relays can be used to activate any of a myriad of options including the activation of warning lights, alarms, exhaust fans, automatic valve operation, etc. Typically, users will use system integrated logic to program a detector or controller to activate a relay when an alarm or combination of alarm set points have been reached. In a fail-safe* operation, relays are normally energized and de-energized upon alarm activation. In a non-fail-safe* operation, the relays are normally de-energized. Relays have normally open (NO) or normally closed (NC) contacts. The NO or NC designations refer to the state of the contacts when they have not been activated; i.e., power is not applied to the relay. NO contacts are those that are not completing a circuit unless the relay becomes energized. NC contacts will open when the relay is energized. WARNING LIGHT RELAY CIRCUIT NOT ENERGIZED RESET/ UP ALM1 ALM2 FAIL % RESET/ UP ALM1 ALM2 FAIL NEXT 0 RXD LEL Me a s u r e me n t WARNING LIGHT RELAY CIRCUIT ENERGIZED % RS485 N a me RXD RS485 N a me TXD 6000 Universal Transmitter EDIT DOWN/ CAL L1 Transmitter below user configured alarm set-point. Relay is not energized; the circuit to illuminate warning light is not completed. * Refer to the glossary for an explanation of this term 42 NEXT 0 LEL Me a s u r e me n t TXD 6000 Universal Transmitter DOWN/ CAL EDIT L2 L1 Transmitter above user configured alarm set-point. Relay energizes, completing the circuit and illuminating the warning light. L2 SENSOR TECHNOLOGY The science behind gas and flame detection has vastly improved in recent years and continues to evolve. Miniaturization of components, more efficient power utilization, and new detection methods lead the way in providing solutions to safeguarding people and equipment from the hazards of toxic and combustible gases, vapors and aerosols. To understand the best methods available to meet different process needs, Scott Safety constantly tests and evaluates emerging technologies. Our team of experts can explain the benefits and limitations of the different sensor types available and how they can be best utilized to provide the safest protection. 43 CATALYTIC BEAD (CAT BEAD) SENSORS Beads consist of a wrapped coil of platinum wire covered with a ceramic base and then coated with a precious metal to act as the catalyst. The active, or sensing, bead is heated to temperatures up to 1000°C to allow the oxidation* of combustible gases to occur. The reference, or nonsensitive, bead remains at a lower temperature and is separated from the active bead by a thermal barrier. The resistance of the two beads is measured and compared using a Wheatstone bridge. WHEATSTONE BRIDGE CIRCUIT: When gas burns on the active bead causing the temperature to increase, the resistance of the bead changes. As the bridge becomes unbalanced, the offset voltage is used to determine the measured value. OUTPUT N BE VE C E AD DC POWER TI RE BE TI E R1 FE C AC N RE RE THERMAL BARRIER AC FE AD RE VE BE AD TOP VIEW (Internal) BE AD ADVANTAGES 1. Proven technology 2. Low cost 3. Can be used to detect wide range of combustible gases 4. Proven technology for the detection of hydrogen * Refer to the glossary for an explanation of this term 44 LIMITATIONS 1. High power 2. Susceptible to poisoning from chlorine, silicones and acid gases 3. Cannot be used in an oxygen deficient atmosphere 4. Unable to discriminate between different types of combustible gas R1 balances the right side of the circuit. The combustion that occurs across the active bead leads to an unbalanced output of the circuit. This value is then used to determine the concentration of combustible gas present. INFRARED SENSORS Infrared light is a part of the electromagnetic spectrum that is close to, but not, visible light and can be felt as heat. The wavelength profile of infrared is expressed in microns between 0.7 μm and 300 μm. Hydrocarbon combustible gas molecules can absorb certain wavelengths of IR called absorption bands and allow other wavelengths to transmit through. Each gas has a specific set of IR wavelengths that will absorb, called the absorption spectrum. This provides a unique identifier to monitor and detect target gases. Infrared sensors are designed to detect specific types of gases utilizing filters that will only allow a narrow band of wavelengths to pass through to a detector. This works on the same principle as a pair of sunglasses that filter out some of the sun’s UV rays and visible light from your eyes. Infrared Light Source Lens Absorption of Infrared Light by the Target Gas Transmittance Filters Active Detector Reference Detector The infrared light source pulses on and off at a set frequency to increase the detectors’ sensitivity and reduce noise. The infrared light source and the detectors are isolated from the gas sample through the use of mirrors, lenses, or filters preventing any contamination of the sensor. Absorption of the infrared light occurs as the beam shines through a gas sample. Not all of the light is absorbed though, some IR light transmits through the gas sample at a lower intensity from the original source light. Each detector has separate filters. The reference detector has a filter that is tuned to part of the spectrum where the IR is fully transmitted. The filter of the active detector is tuned at the same wavelength of the absorption band of the target gas. The difference in outputs from each detector is what makes the detection of a target gas possible. OPEN PATH TECHNOLOGY Open path technology works on much the same principle as a stand alone sensor over a much larger scale. Open path infrared sensors separate the light source from the detectors. The beam from the infrared light source is projected across a large path to a detector. This is useful in outdoor applications or when detecting gases across a perimeter of a specified area. However, while larger areas can be covered with fewer sensors using open path technology, the projected beam can be blocked or absorbed and interfere with accurate results. 45 ADVANTAGES 1. Long life 2. Fast response time 3. Resistant to contamination 4. Open path can detect over a large area LIMITATIONS 1. Unable to detect hydrogen 2. Open path can be interfered with from precipitation, fog or IR sources 3. Can be costly 4. Unable to discriminate between different types of hydrocarbons ELECTROCHEMICAL (E-CHEM) SENSORS Electrochemical sensors provide monitoring for a wide variety of toxic gases. An aqueous electrolyte solution provides a conductive path for ions* to travel between electrodes*. Target gases are either reduced or oxidized at the working electrode resulting in a current flow between the working and the counter electrode. The reference electrode provides a zero reference point from which the resulting difference in potential between the counter and working electrodes can be compared. Target gas levels can be measured in parts per million (ppm). RULE OF THUMB: If you can’t put your head into the environment being monitored, don’t use an E-chem sensor to do the monitoring. -No liquid environments -No extreme temperatures or pressures -No high velocity duct mounts ADVANTAGES 1. Low power 2. W ide range of gases can be detected 3. Low cost LIMITATIONS 1. Typically requires oxygen to work 2. Life span shortened in arid or high humidity conditions * Refer to the glossary for an explanation of this term 46 External connection to transmitter COUNTER ELECTRODE Provides surface for the opposing reaction of the target gas from the working electrode Either electrode may be the anode or cathode depending on the target gas WORKING ELECTRODE Acts as a catalyst for the chemical reaction of the gas GAS PERMEABLE MEMBRANE Gas diffuses through this membrane, and it also provides physical barrier for electrolyte REFERENCE ELECTRODE Stable source for comparison with the working electrode. No current flows through the reference electrode ELECTROLYTE Provides the ion flow between electrodes during the chemical reaction PHOTO IONIZATION DETECTOR (PID) Photo ionization detectors (PIDs) use ultraviolet light to ionize volatile organic compounds (VOCs)* and detect them as current through two oppositely charged electrodes. VOCs easily evaporate at room temperature. Many VOCs are present in a wide variety of applications as a byproduct of aerosols, solvents, wastewater management facilities and pharmaceutical processing. A single PID sensor is capable of detecting a wide number of VOCs. However, the sensor cannot distinguish between two different types of VOCs. Any molecule in the space between the two electrodes is ionized if its ionization potential (IP) is smaller than the energy of the lamp in electron volts (eV). The ions created in the space between the two oppositely charged electrodes migrate to the electrode with the opposite charge as the ion molecule. The output of the sensor as an ionic current is directly proportional with the concentration of VOCs in ppm levels. 1. GAS CHAMBER 3. 2. * Additional information regarding this topic can be found in the glossary 47 FILTER/SAMPLE PORT Electrodes Gas Chamber UV Lamp DETECTION PROCESS 1. Gas enters through the porous membrane and fills the gas chamber. 2. UV light emits from the lamp into the gas chamber and ionizes molecules between the electrodes. 3. Positively charged ions migrate to the negative electrode and negative ions migrate to the positive electrode to create an ionic current. The ionic current is translated by the gas detector as a ppm of the overall gas sample. The higher the current, the greater the number of ionized VOCs. PHOTO IONIZATION DETECTOR (PID) 10 eV 11.2 eV e lfid Su ct H yd m ro g on en ia O Am e in or hl ha Et Pr op 1- an e C ne H oc ADVANTAGES LIMITATIONS 1. PID sensors detect a wide range of VOCs and can be used in a wide range of applications. 2. Concentration of organic vapors is detected in ppm levels. 1. Because the sensor ionizes any molecule with an ionization potential less than the lamp’s potential, the sensor cannot specifically identify which gas is present. 2. PIDs are sensitive to humidity and window contamination that may affect sensor accuracy. 48 11.5 eV e an e an ex bo ar C ta ne 10.9 eV e su Di n e on et Ac lo yc C 10.6 eV lfid ta ep H e en nz Be ne ue To l 10.3 eV Pr op 9.7 eV ol 9.4 eV This lamp can detect the broadest spectrum of VOCs, however, has a very short life span, typically only a few hundred hours. Humidity, oxygen and CO2 levels can interfere and affect the sensitivity of detection. 11.7 eV an 9.1 eV This is the most commonly used lamp. It offers a broad detection of gases, 10.6 eV high stability and a 2-3 year lifespan. ne 8.8 eV This lamp requires the lowest power and has the highest life-span, but limited detecting capability. 9.8 eV ULTRAVIOLET (UV) LAMP The UV lamp is the source of radiation that ionizes VOCs. The UV energy of the lamp and the ionization potential of the VOCs is measured in electron volts (eV). The most common lamp ratings are 9.8 eV, 10.6 eV and 11.7 eV. METAL OXIDE SEMICONDUCTER (MOS) SENSORS Metal oxide semiconductor gas sensors utilize thin films of metal oxides placed upon a silica substrate. The substrate is heated around 200-600°C while the resistance of the metal oxide is continuously monitored. The sensor responds to changes in the atmosphere as the resistance value of the metal oxide changes when exposed to target gases. Thin layer of metal oxide (SnO2, TiO2, In2O3, WO3, NiO, etc.) Silica substrate with sensing electrodes to measure resistance value of the metal oxide Heater coil ADVANTAGES 1. Performs well in high/low humidity 2. Long life span 3. Can detect both low ppm of toxic gases and higher concentrations of combustible gases 49 LIMITATIONS 1. Nonlinear response 2. Subject to false alarms due to cross-interferences from reactive gases 3. Subject to dormant response if not tested regularly SENSOR PERFORMANCE FACTORS Choosing the right sensor type for gas monitoring involves an assessment of many factors. Target Gas Identify the target gases that have a potential for providing a hazard in the process. Most sensors are applicable to mostly toxic or mostly combustible gas monitoring. However, some sensor types are capable of monitoring for either. Situations where several gases may pose a threat may be monitored for a presence of a hazardous gas. GENERALLY TOXIC Electrochemical GENERALLY COMBUSTIBLE Infrared Catalytic Bead GENERALLY BOTH PID MOS Cost Sensor Placement Cost of different sensor types should play a factor in determining what sensors best suit the needs of a gas monitoring situation. Maintenance and calibration can also play a significant role in determining the overall cost of ownership over the lifetime of a sensor. Sensors that may have a higher initial cost, may in fact have a lower overall cost of ownership over the life of the sensor and vice versa due to sensor life, calibration, bump testing* and potential sensor contamination. At no time should cost be considered over safety. Always use the correct sensor type for the job. LOWER INITIAL COST Electrochemical PID Catalytic Bead Sensor effectiveness is directly impacted by sensor placement. Even the best sensor will not be able to detect a hazard if placed too far from release or receptor points. Consider zoned or voting coverage areas where multiple sensor points effectively provide a maximum, redundant coverage area to minimize false alarms and account for barriers and air currents, all potential release points. Refer to designing a gas detection system for more information. * Refer to the glossary for an explanation of this term 50 LOWER LIFETIME COST MOS IR SENSOR PERFORMANCE FACTORS Choosing the right sensor type for gas monitoring involves an assessment of many factors. Temperature/ Humidity Monitoring processes in severe environments can affect certain sensor types. All sensor types are rated for use in a specific temperature range. Some sensors can be affected in high humidity environments where water vapors can interfere with readings. Refer to Sensor Technology on Pages 44-51 for more information. Oxygen Content In applications where oxygen may be displaced or not present in a gas sample, the sensor type should be considered. E-chem, cat bead, MOS, and paper tape sensors will not perform as designed without oxygen present. Power Consumption Some sensor types consume much more power than others. This factor is important when considering whether a technology is appropriate for use in a fixed or portable detection device. Fixed detection systems must have appropriate power supplies to maintain the current necessary for sensor operation. Follow sensor manufacturer’s installation instructions. Cross Interference* Nearly all sensor types can be susceptible to interferences from other than target gases. Sensor manufacturers employ different methods to counter the effects of this through the use of filters, sensor construction materials, and preprogrammed expected response functions based on target gas characteristics. Always refer to manufacturer’s recommendations when performing calibrations and installation instructions to ensure the highest quality of gas detection response. In some technologies, a sensor can be calibrated with an appropriate cross interferent gas, if the target gas is unobtainable or difficult to be applied in field conditions. In this case, a K-factor* should be applied to the calibration values. Follow manufacturer’s calibration methods to achieve desired sensor performance. * Refer to the glossary for an explanation of this term 51 FLAME DETECTION Flame detection is an important part of overall process monitoring, especially when the process involves combustible gases or materials. Flame sources generate radiation that may or may not be visible to the human eye. Flame detection technology is able to detect flame across a wider view of the electromagnetic spectrum by detecting infrared and/ or ultraviolet sources of radiation. The combustible fuel source affects what type of radiation is generated. Flame detection sensor technologies are available for indoor or outdoor use and some have high immunity to false alarms that could be generated from solar radiation, welding or hot spots. Common technologies include single, multi and triple IR detection, UV detection, and combined UV/IR detection. Microwave Radio Wave Infrared Visible Spectrum FLAME DETECTION SENSOR TYPES IR Array Long Range, Able to Locate the Angular Position of the Flame within the Field of View Single IR Low Cost, Indoor Use Multi IR Low Cost, High Speed of Response, Indoor and Outdoor Use, Low False Alarms, Detects Hydrogen Based Flames Triple IR Indoor and Outdoor Use, Long Detection Range, Highest Immunity to False Alarms UV Detects Hydrogen Based Flames and Hydrocarbon Based Fuel and Gas Fires UV/IR Indoor and Outdoor Use, Long Detection Range, High Immunity to False Alarms 52 THE ELECTROMAGNETIC SPECTRUM Flame and gas detection technology use sensors that can detect across a much wider range of the spectrum than what the human eye or closed circuit cameras are able to see. Many fuel sources and gases produce flames and radiation beyond the visible spectrum. These invisible sources of radiation are easily detected using advanced sensor technology. Radiation Emitted from Different Flame Types Ultraviolet X-Ray Gamma Ray STANDARDS AND APPROVALS Navigating through the certifications and approvals of gas detection equipment can sometimes prove to be a challenge. With so many markings available, it is important to understand the significance and value of these certifications and how they apply to gas detectors. Different markets and regions may require adherence to different standards, but the overall goal is to ensure equipment will perform safely in hazardous locations and comply with an established protection method such as intrinsic safety. A hazardous location exists when: - Flammable gas, vapor, or mist exists with a concentration of > 10% LEL - Oxygen levels are < 19.5% or > 23.5% - Atmospheric concentration of any hazardous substance which could result in exposure in excess of the published dose per OSHA regulations - Airborne combustible dust > 100% LEL - Any other atmospheric condition immediately dangerous to life or health (IDLH) GAS DETECTION PRODUCTS THAT MAY REQUIRE APPROVAL -Portable and fixed gas detectors -Open path detectors -Sensors installed within detectors -Multi-gas gas detectors -Multi-gas sensors -Flammable gas detectors -Combustible gas detectors -Some remote accessories connected to detectors -Flame detectors Intrinsic safety is a design technique applied to electrical equipment and wiring used in hazardous or potentially hazardous locations. Limiting the energy, electricity, and thermal properties of the equipment to prevent ignition of a hazardous atmosphere are the cornerstones of intrinsic safety. Note: None of the markings on this page constitute any approval authority or that certification has been given to this document. 53 HAZARDOUS AREA CLASSIFICATIONS Hazardous area classifications can be best understood by knowing the standard to which they apply. Generally, there are three standards of classification. European/IEC/Cenelec standards use the zone classification. In North America, two standards may be used, NEC* 500 (Division Classification) or NEC 505 (Zone Classification—mirrors the European/IEC*/Cenelec* standards). ZONE 0 Explosive gas or air is continuously present Greater than 1000 hours/year ZONE 1 Explosive gas or air is likely to exist Greater than 10 but less than 1000 hours/year ZONE 2 Explosive gas or air is not likely to exist Less than 10 hours/year DIVISION 1 Is equal to either Zone 0 or Zone 1 Greater than 10 hours/year DIVISION 2 Is equal to Zone 2 Less than 10 hours/year GROUPINGS Gases Acetylene Hydrogen Ethylene Propane Methane Dust Magnesium Coal Grain Fibers NEC 500 CLASS I Group A Group B Group C Group D N/A CLASS II Group E Group F Group G CLASS III NEC 505 European/IEC/CENELEC Group Group Group Group Group II II II II I C C B A *European/IEC/Cenelec standards do not subdivide into classes or materials. TEMPERATURE CODES Temperature codes are used to identify the maximum surface temperature a certified gas detector may achieve and still be intrinsically safe. Max Surface Temp (°C) 450 300 280 260 230 215 200 NEC 500 T1 T2 T2 A T2 B T2 C T2 D T3 * Refer to the glossary for an explanation of this term 54 NEC 505 European/IEC/CENELEC Max Surface Temp (°C) T1 T2 T3 180 165 160 135 120 100 85 NEC 500 T3 A T3 B T3 C T4 T4 A T5 T6 NEC 505 European/IEC/CENELEC T4 T5 T6 PROTECTION METHODS AND STANDARDS Protection methods are added to markings and certifications to demonstrate to what level of product safety that the gas detector has been designed. There are several different standards by which equipment may be tested in order to demonstrate product safety. Protection Method (Meaning) Division ia - Intrinsic Safety up to 2 faults Exia - Canada, Intrinsically Safe ib - Intrinsic Safety to a single fault Intrinsically Safe System Explosion Proof d - Flame Proof p - Pressurization (X, Y) - Purged/Pressurized (Z) - Purged/Pressurized e - Increased Safety m - Encapsulation o - Oil Immersion q - Powder Filled Non-Incendive/Non-Ignition Capable Arching/Heating Parts n - Protection Special Requirements 2 protection methods 1 1 1 2 2 - Canada CSA C22.2 No. 157 C22.2 No. 30 NFPA 496 NFPA496 C22.2 No. 213 - US Zone Canada CSA ANSI/UL* ANSI/ISA Zone Cenelec IEC FM3610/UL913 FM3615/UL1203 NFPA 496 NFPA496 FM3611/UL1604 - 0 1 1 1 1 0 1 1 2 - E60079-11 E60079-11 E60079-1 E60079-2 E60079-7 E60079-18 E60079-6 E60079-5 E60079-15 - 60079-11 60079-11 60079-1 60079-7 60079-18 60079-6 60079-5 60079-15 - 12.02.01 12.02.01 12.22.01 12.04.01 12.16.01 12.23.01 12.26.01 12.25.01 12.22.02 12.00.01 0 1 0/1 1 1/2 1 1 1 1 2 0 EN 60079-11 EN 50020 EN 50039 EN 60079-1 EN 60079-2 EN 60079-7 EN 60079-18 EN 50015 EN 50017 EN 60079-15 EN 50284 60079-11 60079-11 60079-25 60079-1 60079-2 60079-7 60079-18 60079-6 60079-5 60079-15 60079-26 Standards are continuously being revised and are subject to change. Consult local regulatory agencies for most current standards. * Refer to the glossary for an explanation of this term 55 Global (IEC) Europe (CENELEC) North America - Class I (Flammable Gas or Vapor) NEMA CLASSIFICATIONS/INGRESS PROTECTION National Electrical Manufacturers Association (NEMA) classifications represent an electrical enclosure’s ability to protect internal components against the external environment. HAZARDOUS LOCATIONS 56 Indoor 12 12K 13 Indoor/Outdoor NONHAZARDOUS LOCATIONS 1 2 5 3 3R 3S 4 4X 6 6P Prevents hand contact with internals Protects against falling dirt and water Protects against settling airborne dust, lint, fibers; protects against dripping and light splashing of liquids Protects against falling airborne dust, lint, fibers; protects against dripping and light splashing of liquids; no knockouts Protects against falling airborne dust, lint, fibers; protects against dripping and light splashing of liquids; with knockouts Protects against falling airborne dust, lint, fibers; protects against spraying, splashing, and seepage of water and oil Protects against windblown dust, rain, and sleet; undamaged by ice Protects against falling rain and sleet; undamaged by ice Protects against falling dust, rain, and sleet; undamaged by ice Protects against falling dust, rain, sleet, splashing and hose directed water; undamaged by ice Protects against falling dust, rain, sleet, splashing and hose directed water; undamaged by ice, corrosion protected Protects against falling dust, rain, sleet, splashing and hose directed water; prevents water entry when briefly submerged; undamaged by ice Protects against falling dust, rain, sleet, splashing and hose directed water; prevents water entry during prolonged submerging; undamaged by ice Indoor 7 9 F  or use in Class I, Groups A, B, C, and D F  or use in Class II, Groups E, F, and G Indoor/ Outdoor 8 F  or use in Class I, Groups A, B, C, and D Mining 10 M  eets the requirements of MSHA (Mine Safety and Health Administration) IEC Publication 60529 Classification of Degrees of Protection Provided by Enclosures provides a system for specifying protection provided by enclosures of electrical equipment. The rating consists of the letters IP followed by two digits. The first digit is representative of the protection provided against the ingress of solids. The second digit is representative of the protection provided against the ingress of liquids. 1st Number: Protection Against Solids 2nd Number: Protection Against Liquids 0 No protection provided 1 Protection from objects greater than 50 mm Protection from objects 0 No protection provided 1 Protection from vertically falling water drops Protection from falling water 2 greater than 12 mm 2 drops up to an angle of 15° 3 Protection from objects 3 Protection from spraying water up to 60° from vertical 4 Protection from objects 4 Protection from splashing water 5 Protection from dust 5 Protection from low pressure water jets in all directions 6 6 water jets in all directions greater than 2.5 mm greater than 1.0 mm Dust tight enclosure Protection from high pressure 7 Protection from temporary submersion up to 1 meter 8 Protection from submersion in water greater than 1 meter ATEX ATEX directives provide for the minimum standards applicable to equipment used in explosive atmospheres. Directive 94/9/EC, article 100a defines the classifications and intended uses with respect to safety, design, and manufacturing of these devices. Directive 1992/92/EC, article 137 defines under what conditions these devices should be used by end users to prevent, avoid, and control the hazards associated with explosive atmospheres. ATEX MARKINGS CENELEC ATEX MARKINGS ADDITIONAL ATEX MARKINGS #### E Ex ia IIA T4 II 3 G Flammable Substance: Methane Coal Dust G - Gas, vapors D - Dust E - Complies with EN50014 A - Complies with NEC 505 Level of Protection: M1 - Very High, for mines M2 - High, for mines 1 - Very High 2 - High 3 - Normal Explosion protected Protection method: ia - Intrinsic Safety (2 faults) ib - Intrinsic Safety (1 fault) Exia -Intrinsic Safety (Canada) e - Increased Safety n - Protection (abbreviated list) Gas Group: I - Methane IIA - Propane IIB - Ethylene IIC - Acetylene, Hydrogen Temperature Class: T1 - 450 T2 - 300 T3 - 200 T4 - 135 T6 - 85 (abbreviated list) CE Mark Note: None of the markings on this page constitute any approval authority or that certification has been given to this document. 57 Notified Body Number for Quality System EU ATEX Mark Equipment Group: I - Mines II - Surface CE MARKING CE is an abbreviation for the French phrase Conformité Européene, meaning European Conformance. CE marking is a declaration from the manufacturer that their product conforms to all applicable directives adopted by the EEA (European Economic Area) and is a requirement for the product to be sold into any of the countries in this group. Unlike hazardous location approvals, the manufacturers are solely responsible for ensuring their product’s conformance to these directives which were developed using IEC and Cenelec standards. Further guidance on affixing the CE mark to products can be found in the Guide to the Implementation of Directives Based on the New Approach and the Global Approach; commonly referred to as “The Blue Book” and published by the European Commission. TARGET MARKETS: EUROPEAN ECONOMIC AREA Austria Greece The Netherlands Belgium Hungary Norway Bulgaria Iceland Poland Cyprus Republic of Ireland Portugal Czech Republic Italy Romania Denmark Latvia Slovakia Estonia Liechtenstein Slovenia Finland Lithuania Spain France Luxembourg Sweden Germany Malta United Kingdom Note: None of the markings on this page constitute any approval authority or that certification has been given to this document. 58 CSA INTERNATIONAL CSA International is an organization that provides performance testing in agreement with national and international standards. CSA tests products to meet standards directed by the American National Standards Institute (ANSI), Underwriters Laboratories (UL), and Canadian Standards Association (CSA). CSA is also a Nationally Recognized Testing Laboratory (NRTL) by the Occupational Safety and Health Administration (OSHA) in the U.S., and in Canada by the Standards Council of Canada (SCC). CSA works closely with ATEX and IECEx to operate worldwide. CSA provides certification testing for product safety operating in a hazardous area. DIVISION SYSTEM* DIVISION 1 Flammable gas, vapor, or combustible dusts continuously, intermittently, or periodically present. DIVISION 2 Volatile flammable liquids or flammable gases present, but confined within closed containers or systems; could escape by abnormal operation or fault conditions. CLASS I CLASS II CLASS III Group A Group B Group C Group D N/A Group E Group F Group G ZONE SYSTEM ZONE 0 Gas, vapor, or mist is present continuously or for long periods. ZONE 2 Gas, vapor, or mist is likely to be present. ZONE 2 Gas, vapor, or mist is not likely to be present. If it is present, it will only be for a short period of time. Acetylene Hydrogen Ethylene Propane Methane Metal dust, magnesium Carbon dust Flour, starch, grain Fibers, cotton Group IIC Group IIC Group IIB Group IIA Group I * Refer to the glossary for an explanation of this term Note: None of the markings on this page constitute any approval authority or that certification has been given to this document. 59 COUNTRIES THAT ACCEPT CSA CERTIFICATION AMERICAS Argentina Brazil Canada Mexico United States ASIA PACIFIC Australia China India Japan New Zealand South Korea Taiwan EUROPE Austria Belgium Denmark Finland France Germany Greece Iceland Ireland Italy Liechtenstein Luxembourg Netherlands Norway Portugal Romania Slovenia Spain Sweden Switzerland OTHER Russia South Africa CSA uses both the division system and the zone classifications. Refer to page 54 for more information. UNDERWRITERS LABORATORIES Underwriters Laboratories (UL) is both a Standard Developing Organization (SDO) and Nationally Recognised Testing Laboratory (NRTL) that develops standards and performs testing to ensure products are safe for use in hazardous environments. UL is not a government agency; however, it is approved by the Occupational Safety and Health Administration (OSHA). UL works closely with ATEX and IECEx standards to operate worldwide. UL CERTIFICATIONS ARE ACCEPTED BY 98 COUNTRIES WORLDWIDE, INCLUDING: ASIA PACIFIC EUROPE LATIN AMERICA Australia Austria Italy Argentina China Belgium Latvia Brazil Hong Kong Bulgaria India Cyprus Indonesia Lithuania Luxembourg NORTH AMERICA Czech Republic Malta Canada Japan Denmark Netherlands U.S.A. Korea Estonia Poland Mexico Malaysia Finland Slovakia New Zealand France Slovenia NON-EUROPEAN Philippines Germany Spain Croatia Singapore Greece Sweden Norway Taiwan Hungary Switzerland Russia Thailand Ireland U.K. Ukraine Note: None of the markings on this page constitute any approval authority or that certification has been given to this document. 60 IECEx IECEx is managed by industry representatives including governing bodies, manufacturers, and end users to ensure compliance with worldwide standards for safety of equipment used in hazardous locations (Ex). The IECEx Scheme is an international certification scheme covering equipment that meet the requirements of International Standards; most notably IEC 60079. THE SCHEME PROVIDES: A single international Certificate of Conformity (CoC) that requires manufacturers to successfully complete: • Testing and assessment of samples for compliance with Standards resulting in a Test and Assessment Report (ExTR) • Assessment and auditing of manufacturers facilities resulting in a Quality Assessment Report (QAR) • Ongoing surveillance audits of manufacturers' facilities The IECEx System comprises several systems. The United States participates in the full IECEx Certified Equipment Scheme. Currently Australia, New Zealand, and Singapore accept that the IECEx Certificate of Compliance meets all of the national requirements for Ex Certification meaning no further national testing is required. Countries that do require a national certification will typically accept the results from the test report (ExTR). Many countries have national standards that are already based upon IEC standards, such as Russia (GOST-R), China (CQST), Brazil (InMetro), and Canada (CSA accepts IEC standards). Note: None of the markings on this page constitute any approval authority or that certification has been given to this document. 61 IECEx PARTICIPATING COUNTRIES Australia Canada Croatia Denmark France Hungary Italy Korea Netherlands Norway Serbia Russia Slovenia Sweden Turkey United States Brazil China Czech Republic Finland Germany India Japan Malaysia New Zealand Poland Romania Singapore South Africa Switzerland United Kingdom FACTORY MUTUAL The Factory Mutual Approvals Division determines the safety and reliability of equipment, materials, or services utilized in hazardous locations in the United States and elsewhere. Factory Mutual certifies to NEC (National Electrical Code) standards for hazardous locations, NEC Standard 500 (Division classification) and NEC Standard 505 (Zone classification). For a product to receive approval, it must meet two criteria. First, it must perform satisfactorily, reliably, and repeatedly as applicable for a reasonable life expectancy. Second, it must be produced under high quality control conditions. Factory Mutual also has inter-laboratory agreements and can certify to Canadian and European standards. Factory Mutual certifications are globally recognized and they can test to ATEX and IECEx standards for gas detection devices being used in hazardous locations. FM standards 3610 (Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II and III, Division 1, Hazardous (Classified) Locations), 3611 (Nonincendive Electrical Equipment for Use In Class I and II, Div. 2 and Class III, Divisions 1 and 2 Hazardous (Classified) Locations), and 3615 (Explosion Proof Electrical Equipment General Requirements) as well as other relevant recognized standards are used to certify gas detection equipment. Note: None of the markings on this page constitute any approval authority or that certification has been given to this document. 62 SAFETY INTEGRITY LEVEL (SIL) RATINGS SIL or Safety Integrity Level, defined by standard IEC (EN) 61508 (Manufacturer’s requirements), is the measure of risk reduction offered by the safety function provided to a process. SIL ratings use statistical analysis to prove safety systems are designed in such a way as to prevent dangerous failures or to control hazards when they arise. Gas detection equipment may be SIL rated, or suitable for use as part of a larger SIL rated system. However, having a gas detection device that has a SIL rating does not assure safety. Sensor placement is the most important factor in gas detection. Sensors that are not in position to detect hazardous gases and allow a safety action to occur when hazards reach unsafe levels, are essentially ineffective, regardless of SIL rating. The risk reduction factor (RRF) is the expected reduction in risk to the process hazard analysis using a SIL rated system. SAFER SYSTEM SIL RISK REDUCTION FACTOR 4 3 2 1 100,000 to 10,000 10,000 to 1,000 1,000 to 100 100 to 10 Probability of failure on demand (PFD) is the expected number of failures of the safety system. A SIL 2 system would be expected to fail no more than once out of every 100 times. In the worst case scenario, should a safety system not perform and respond to identified hazards, the potential consequences are listed. PROBABILITY OF FAILURE POTENTIAL CONSEQUENCES ON DEMAND (PFD) OF FAILURE 10-5 10-4 10-3 10-2 to to to to 10-4 10-3 10-2 10-1 Fatalities in surrounding community On-site fatalities On-site injuries, perhaps a fatality On-site minor injuries SIL 2 is typically a cost effective target to achieve. Hazards that require a SIL 3 or 4 rating can usually be engineered or have the process changed to lower the risk at less of a cost than designing a safety system to mitigate the hazard. 63 GLOSSARY OF GAS DETECTION TERMS % v/v Volume/volume percentage of a gas mixture. For example, the Earth’s atmosphere is comprised of a mixture of 20.9% oxygen, 78% nitrogen, and 1.1% trace gases. This means there is 20.9% v/v oxygen in the atmosphere. 4-20 mA An analog signal where 4 mA represents a signal equal to 0% of full scale and 20 mA equals 100% full scale. The power usually comes directly from a power supply. 4-20 mA CURRENT LOOP An analog signal where 4 mA represents a signal equal to 0% of full scale and 20 mA equals 100% full scale. The current loop is isolated from the power supply but shares a common ground with the transmitter or controller. ABSORPTION Occurs as a wavelength of infrared radiation passes through a gas molecule. The wavelength loses intensity as it is absorbed by the gas. AC VOLTAGE Alternating Current. Provides power in which electrons travel in both directions. AC power does not degrade rapidly over distance and is relatively easy to convert into lower currents and voltages. ACGIH American Conference of Industrial Hygienists. AEROSOL A suspension of fine solid particles or liquid droplets in a gas. ANSI American National Standards Institute. 64 GLOSSARY OF GAS DETECTION TERMS ASPHYXIANT Refers to a gas whose primary hazard is as a gas that rapidly displaces oxygen. ATEX ATmosphéres EXplosibles, a directive of the European Union that specifies the minimum requirements for improving safety and health protection of workers potentially at risk from explosive atmospheres. AUTO IGNITION TEMPERATURE Temperature higher than the flash point at which a substance will sustain self-combustion independent of a flame or heated element. Sometimes referred as SIT, Spontaneous Ignition Temperature. BOILING POINT Temperature at which a compound changes from a liquid to a gas. BREATHING ZONE Atmosphere immediately surrounding a worker, regardless of whether safe or hazardous. BRIDGE SENSOR CIRCUIT (WHEATSTONE BRIDGE) A circuit that isolates a reference resistor from an active resistor used in a Cat Bead Sensor. As the temperature increases across the active resistor, the resistance will change. The resulting difference in potential from the two resistors translates into an output voltage. BUMP TEST Bump testing verifies the Span Calibration by subjecting the monitor to a known exposure of gas to demonstrate the response is within an acceptable range of the actual concentration. Bump testing also can be used to demonstrate proper activation of alarms and relay circuits. C (CEILING LEVEL) Ceiling level is an exposure limit that must never be exceeded, even for short periods of time. 65 GLOSSARY OF GAS DETECTION TERMS CAS NUMBER Chemical Abstract Service Registry number as determined by the American Chemical Society to uniquely identify each substance in spite of how many common names a substance may have. CALIBRATION Typically occurs in two stages, zero calibration and span calibration. Zero calibration is performed to establish baseline readings of atmospheres that are known to be free of toxic or combustible gases. Span calibration is performed to ensure a monitor detects target gases within specified operating parameters. CATALYTIC BEAD (CAT BEAD OR PELLISTOR) Combustible sensor type that uses an active and reference bead to translate differences in resistance from heat produced through the combustion of gases to translate into a %LEL. CCC China Compulsory Certification mark. CCM Cubic Centimeters per Minute, a measure of the flow of gas particularly important during calibration of sensors. 1 CCM =0.001 LPM = 0.00212 SCFH. CCOHS Canadian Center for Occupational Health and Safety. CE Conformité Européene; a manufacturers’ mark that a product conforms to directives adopted by the European Economic Area. CEC Canadian Electric Code. 66 GLOSSARY OF GAS DETECTION TERMS CENELEC European Committee for Electrotechnical Standardization, technical organization that develops safety and health standards for the European market. CoC Certificate of Conformity; part of the IECEx Scheme. COLD BOOT Resetting a gas detector by removing power completely, and then reapplying power. This may cause additional warm-up time for sensors before the detector reaches its full effectiveness. COMBUSTIBLE Refers to a gas whose primary hazard is the ability to ignite. It is important to note many gases have both combustible and toxic properties. CONFORMAL COATING Protective material applied to printed circuit boards to remove the risk of potential contaminants that could interfere with the proper operation of the electronics such as dust, moisture, and temperature variations. CONTROLLER Part of a fixed gas detection system than can be used to accept multiple inputs to one centralized location for easy monitoring of a large area. CQST China National Quality Supervision and Test Centre for Explosion. CROSS SENSITIVITY/CROSS INTERFERENCE Refers to the ability of gas sensors to detect gases other than what they are intended to. This can be a result of any number of factors ranging from oxidation, catalyst type being used, similar gas properties, or reaction of certain compounds. Proper calibration techniques, filters, and an understanding of the operation of particular types of sensors can help reduce the effects of cross sensitivity. 67 GLOSSARY OF GAS DETECTION TERMS CSA Canadian Standards Association, a certifying agency that evaluates products through a formal process involving examination, testing and follow-up inspection to verify the product complies with applicable standards for safety and performance. DATA ACQUISITION DEVICE A device that performs automatic collection of data from sensors, instruments and devices. DC VOLTAGE Direct Current. Provides power in which electrons flow only in one direction. Power source is usually a battery or solar cell. DC power degrades rapidly over distance. DILUTION ORIFICE A sample gas detection method that introduces ambient air into an otherwise confined space through an opening in the sampling device to allow for greater accuracy on % LEL concentrations. Necessary in sampling gas concentrations that would otherwise lack the necessary amount of oxygen for proper sensor performance. DISTRIBUTED CONTROL SYSTEM (DCS) A control system in which the controller elements are not in a central location, but are distributed throughout the system with each component sub-system controlled by one of more controllers. The entire control system is networked for communication and monitoring. DIVISION Division is the North American method of specifying the probability that a location is made hazardous by the presence, or potential presence, of flammable concentrations of gases and vapors. EEA European Economic Area. 68 GLOSSARY OF GAS DETECTION TERMS ELECTROCHEMICAL (E-CHEM) A gas sensor that measures the current that results from the reaction of the target gas against two or more electrodes. The current generated in the sensor is generally proportional to the gas concentration. ELECTRODE A conductor through which electric current is passed. ELECTRON A particle that carries a negative electric charge. EMI (ELECTROMAGNETIC INTERFERENCE) Electrical interference from conducted voltages and currents through a signal path. EMI can be a particular problem in circuits with low current such as 4-20 mA or in relay protection circuits as the signal noise generated from EMI can cause false readings, alarms, or relay activation. eV (ELECTRON VOLTS) The measurement of ionization potential. EXPLOSION PROOF Electrical devices designed to contain explosions or flames produced within them without igniting the external flammable gases or vapors. ExTR Test and Assessment report; part of the IECEx Scheme. FAILSAFE Refers to an electronically activated circuit, such as a relay, that will fail to a preferred position upon a loss of power. 69 GLOSSARY OF GAS DETECTION TERMS FIXED GAS DETECTION SYSTEM A permanently mounted combination of sensors, transmitters, controllers and relay controlled devices that allow for local and remote monitoring and activation of safety devices. Fixed gas detection systems are highly customizable applications that are designed to mitigate the risk of hazardous areas and dangers posed to workers and equipment. FLASH POINT Temperature at which the vapor emitted by a substance reaches concentrations equal to the lower flammability limit. FM Factory Mutual, a certifying agency that evaluates products will perform as expected and support property loss prevention. GAS STRATIFICATION Failure of gases to mix evenly in the atmosphere due to differences in vapor density, temperatures, and pressure. GENERAL PURPOSE LOCATION Any atmosphere that is not a hazardous location. GOST-R Gosudarstvennyy Standard; Certificate of Conformity for Russia. HAZARDOUS ATMOSPHERE (Hazardous Location, Hazardous Area, Hazardous Situation) An atmosphere that may expose workers to the risk of death, incapacitation, impairment of ability to self-rescue, injury, or acute illness from one or more of the following causes: 1. Flammable gas, vapor, or mist in excess of 10 percent of its LEL 2. Airborne combustible dust at a concentration that meets or exceeds its LEL 3. Atmospheric oxygen concentration below 19.5 percent or above 23.5 percent 4. Atmospheric concentration of any substance for which a PEL is published 5. Any other atmospheric condition that is IDLH. 70 GLOSSARY OF GAS DETECTION TERMS IDLH (IMMEDIATELY DANGEROUS TO LIFE OR HEALTH) Exposure to airborne contaminants that are likely to cause death, immediate or delayed permanent adverse health effects, or prevent escape from such an environment. IEC International Electrotechnical Committee. IECEx Scheme to standardize international certification. IGNITION TEMPERATURE Temperature at which a flammable gas may ignite without a spark or flame source. INGRESS PROTECTION A measure of protection against the intrusion of solid objects including dust, water, tools, body parts, etc. as defined by the Standard IEC 60529. INMETRO Brazilian conformity mark. INTRINSICALLY SAFE Electrical equipment that is incapable of releasing sufficient electrical or thermal energy under normal or abnormal operating conditions to cause ignition of a specific hazardous mixture and air. Equipment must be intrinsically safe to be used in Division 1 environments. IOHA International Occupational Hygiene Association. 71 GLOSSARY OF GAS DETECTION TERMS ION An atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. IP (IONIZATION POTENTIAL) Amount of energy required to remove an electron from an isolated atom or molecule. Measured in eV. IR (INFRARED) A combustible sensor type that measures the absorption of infrared electromagnetic wavelengths as a gas passes through to measure gas levels. In some cases, IR sensors can be used to detect toxic gas concentrations as well or radiation emitted as part of the electromagnetic spectrum with a wavelength longer than visible light. ISA International Society of Automation. ISOLATED 4-20 mA An analog signal where 4 mA represents a signal equal to 0% of full scale and 20 mA equals 100% full scale. The isolation allows the signal path to be isolated from the power supply to the transmitter or receiver and results in a general insensitivity to electrical noise. K-FACTOR A K-factor is used to determine the relative sensor response ratio of the calibration gas to the expected detected gas when the calibration gas is not the same as the detected gas. K-factors are used to allow for the monitoring of a presence of gas, not to achieve accuracy in gas monitoring. A K-factor can be expressed in the formula: (K-Factor) (% Cal Gas) = Adjusted Span Output For example, when calibrating a sensor using 50% LEL propane gas, a K-factor can be applied to achieve readings for butane. Let’s assume the K-factor is 0.75. Using 50% LEL propane gas and multiplying by the K-factor of 0.75, the adjusted span calibration should be done to achieve a reading of 37.5%. This will allow a user to monitor for butane. However, it should be noted, to achieve the most accurate readings for the desired targeted gas, the calibration gas should be the same as the target gas. 72 GLOSSARY OF GAS DETECTION TERMS LATCHING Refers to an activated alarm that will remain activated until user acknowledgement occurs regardless of whether the alarm condition clears. LCO (LOOP CURRENT OFFSET) Refers to a gas transmitter whose electronics operate at < 4 mA. This is the offset current. The standard 4-20 mA signal, or loop current, is still utilized to produce a gas reading from 0 to full scale. LEL (LOWER EXPLOSIVE LIMIT) The Lower Explosive Limit is the percentage of atmosphere below which the concentration of gas mixture to atmosphere is too lean to burn. This is sometimes expressed as Lower Flammable Limit (LFL). LPM Liters per minute, a measure of the flow of gas particularly important during calibration of sensors. 1 LPM = 1000 CCM = 2.12 SCFH. mA Milliamp is a unit of measure of the current of electricity. 1 mA = 0.001 Amp. MODBUS®* A serial communication protocol used to network electronic devices. MOS Metal oxide semiconductor. NEC National Electric Code. NEMA National Electrical Manufacturers Association. * Registered trademark of Schneider Electric. 73 GLOSSARY OF GAS DETECTION TERMS NIOSH National Institute for Occupational Safety and Health. NC (NORMALLY CLOSED Normally Closed refers to a relay contact that removes circuit continuity when activated. NO (NORMALLY OPEN) Normally Open refers to a relay contact that allows circuit continuity when activated. NON-FAILSAFE Refers to an electronically activated circuit, such as a relay, that will remain “as is” upon a loss of power. NON-INCENDIVE Electrical equipment that is incapable of releasing sufficient electrical or thermal energy to cause ignition of a hazardous mixture and air under normal operating conditions. Equipment must be non-incendive to be used in Division 2 environments. NON-LATCHING Refers to an activated alarm that will clear without any user interaction once the alarm condition has cleared. NRTL Nationally Recognized Testing Laboratory. OHM’S LAW Ohm’s Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. P - This is the total power generated in a circuit. It is the product of current and voltage, measured in watts. E - This is the difference in electrical potential between two points of a circuit, measured in volts. Volts are the muscle to move current. I - This is the current, or what flows on a wire, measured in amps. R - This is the resistance of the circuit, or what determines how much electricity can flow in a circuit. As resistance increases, current flow becomes less and vice versa. Measured in ohms. 74 GLOSSARY OF GAS DETECTION TERMS OPEN PATH A type of IR sensor technology that measures gas detection along a line of sight between a transmitter and receiver. OSHA Occupational Safety and Health Administration. OXIDATION Oxidation is a chemical reaction that results in the loss of electrons. Chemicals that cause the loss of electrons are also called oxidizing agents. The oxidation-reduction reaction is typical in an electrochemical sensor. PEL (PERMISSIBLE EXPOSURE LEVEL) Permissible exposure levels are the maximum concentration a worker may be exposed to as defined by OSHA (Occupational Safety and Health Administration). PELs are defined in two ways, TWA and C (C). PFD Probability of Failure on Demand; part of a SIL Rating. PID (PHOTO IONIZATION DETECTOR) A gas detection technology that uses an ultraviolet lamp to ionize the target gas and measures the ionic current between two electrodes to detect it. POISON RESISTANT Catalytic bead sensor’s ability to remain resistant to damaging contaminants such as silicone and solvents while still continuing to detect gas. PORTABLE GAS DETECTION SYSTEM Typically a handheld gas detector capable of detecting 1-5 gases for use in sewers, tanks, and other locations where a fixed detector is either impractical or unable to account for the necessary space and volume needed by personnel. 75 GLOSSARY OF GAS DETECTION TERMS PPB Parts per billion. Measurement of a concentration of a gas per billion parts. 1 ppb = 0.001 ppm. PPM Parts per million. Measurement of a concentration of a gas per million parts. 1 ppm = 1000 ppb or 1 ppm = 0.0001% of sample concentration. PELLISTOR See Catalytic Bead. PROCESS A series of operations performed in the making, treating, or developing of a product. PROGRAMMABLE LOGIC CONTROLLER (PLC) A digital computer used for automation of electromechanical processes. PLCs typically accept numerous inputs and provide multiple outputs. PROTON A particle that carries a positive electric charge. QAR Quality Assessment Report; part of the IECEx Scheme. RECEPTOR POINT Location where hazardous gases cause a threat to personnel, property, or facilities. RELEASE POINT Location where hazardous gases can potentially be released. RELATIVE DENSITY Ratio of the density of gas compared with ambient atmosphere. Greater than 1.0 indicates the gas is heavier than air. 76 GLOSSARY OF GAS DETECTION TERMS REMOTE ALARM RESET An option sometimes available on either a fixed gas detector or controller that allows users to acknowledge an alarm or deactivate a relay switch from a remote location. RFI (RADIO FREQUENCY INTERFERENCE Electrical interference from unwanted reception of radio signals originating from any number of wireless communication devices. RFI can be a particular problem in circuits with low current such as 4-20 mA or in relay protection circuits as the signal noise generated from RFI can cause false readings, alarms, or relay activation. RRF Risk reduction factor; part of a SIL rating. RS-232 A digital form of communication over a networked interface. Allows for a single point to point communication over a distance of 50 or less feet. RS-485 A digital form of communication over a networked interface. Allows for multiple point to point communications of up to 32 devices over a distance of up to 4000 feet. SCC Standards Counsel of Canada. SCFH Standard cubic feet per hour, a measure of the flow of gas particularly important during calibration of sensors and determining the applicability of duct mounted gas detection. 2.12 SCFH = 1000 CCM = LPM. SENSOR HEAD A part of a fixed gas detection system that facilitates the electrical interface of the sensor with the transmitter or controller. May be mounted remotely or affixed to a transmitter. 77 GLOSSARY OF GAS DETECTION TERMS SIL (RATING) Safety Integrity Level, a safety level rating as defined by the standard IEC 61511 or EN 61511. The level is determined by analyzing the safety function of separate and combination gas detection systems and the risk reduction they create to the safety hazards. STEL (SHORT TERM EXPOSURE LIMIT) Short term exposure limit is defined by ACGIH (American Conference of Governmental Industrial Hygienists) as the concentration to which workers can be exposed continuously for a short period of time without suffering from irritation, chronic or irreversible tissue damage, or narcosis of sufficient degree to increase the likelihood of accidental injury, impair self-rescue or reduce work efficiency. T90 Time it takes a sensor to respond to 90% of full reading when exposed to target gas. TLV (THRESHOLD LIMIT VALUE) Threshold limit values are established by the ACGIH (American Conference of Governmental Industrial Hygienists). They are the levels to which a worker can be exposed to a chemical each day for a working lifetime without adverse health concerns. These limits are guidelines and not regulated by law. TOXIC Refers to a gas whose primary hazard is as a breathing contaminant or poison. It is important to note many gases have both combustible and toxic properties. TRANSMITTANCE Measurement of the intensity of infrared radiation that has passed through gas molecule. TRANSMITTER A device that receives, displays, and transmits the electronic signals from gas sensors. TRIP HIGH A set point that causes the activation of an alarm or relay when a gas reading exceeds a certain value. 78 GLOSSARY OF GAS DETECTION TERMS TRIP LOW A set point that causes the activation of an alarm or relay when a gas reading falls below a certain value. TWA (TIME WEIGHTED AVERAGE) Time weighted average is an average value of exposure over the course of an 8 hour work shift. UEL (UPPER EXPLOSIVE LIMIT) The Upper Explosive Limit is the percentage of atmosphere at which the concentration of gas mixture to atmosphere is too rich to burn. This is sometimes expressed as UFL (Upper Flammable Limit). UL Underwriters Laboratories, a certifying agency for the electrical safety of devices; including those used in hazardous atmospheres. ULTRAVIOLET Radiation emitted as part of the electromagnetic spectrum with a wavelength shorter than visible light. VAPOR A gaseous compound in equilibrium with its liquid or solid phase. VAPOR DENSITY A measure of the density of a gas or vapor relative to ambient air (Vapor Density 1.0) Those gases or vapors with densities > 1.0 will settle at lower elevations. Those gases or vapors with densities < 1.0 will settle at higher elevations. VAPOR PRESSURE The pressure of the vapor in equilibrium with its liquid or solid phase at the given temperature. As temperature increases, the vapor pressure increases nearly exponentially with temperature. 79 GLOSSARY OF GAS DETECTION TERMS VOC Volatile organic compound. VOTING CONFIGURATION A fixed gas detection system set up to activate alarm functions only when a preconfigured set of values has been reached on multiple points of detection; helps to reduce false alarm conditions. ZONED CONFIGURATION A fixed gas detection system set up to cover a large surface area with multiple points of detection; useful when release points cannot be easily predicted. ZONE Zone is the international method of specifying the probability that a location is made hazardous by the presence, or potential presence, of flammable concentrations of gases and vapors. 80 Scott Safety continues to build and forge sustained partnerships with our customers to understand and meet their individual needs. We recognize the importance of industry best practices and certify our products through intensive testing to be of the highest quality. We are focused on developing new technologies to make workers safer each and every day, and we take pride in doing it. Visit our website at www.scottsafety.com or contact us at 1.800.247.7257 to learn more about the products and services we offer. Scott Safety is ready to share our experience and provide solutions to our customers. 81 SCOTT SAFETY Monroe Corporate Center 4320 Goldmine Road Monroe, NC 28110 Telephone 1.800.247.7257 FAX 704.291.8330 www.scottsafety.com Printed in the USA © 2011 Scott Safety. SCOTT, the SCOTT SAFETY Logo, and Scott Health and Safety are registered and/or unregistered marks of Scott Technologies, Inc. or its affiliates. HS 6866A ISO 9001 Registered.