Det-Tronics Compliance Tips: Fire and Gas Detection and Suppression Systems for LNG Facilities (White Paper)
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Fire and Gas Detection and Suppression
Systems for LNG Facilities
Planning for functional safety requires an
understanding of process hazards, relevant
industry standards and local codes, and
available product and system solutions.
Liqueﬁed natural gas (LNG) is 600 times denser than the
gas form, making the economics to transport LNG more
attractive (and more feasible) than transporting natural gas
in pipelines over great distances across oceans. There are
several proprietary processes used to make LNG, all of
which involve refrigerating the gas and then expanding it
to turn into a cryogenic liquid. Inherent in these processes
are the risks associated with spills and leaks as well as
other process hazards.
Non-ﬂammable as a cryogenic liquid, when LNG warms,
it vaporizes (re-gases) and may form a ﬂammable mixture
upon reaching a concentration of between 5% and 15%
methane-to-air. If LNG should leak to the environment, it
will quickly vaporize and form a rising cloud of methane
gas, without leaving a residue. The hazard is created when
the cloud forms a ﬂammable concentration that presents
a risk for ignition. If the leak occurs within a conﬁned area,
there is a potential for ignition with explosion. The heat
release rate from an LNG pool ﬁre is approximately 60%
greater than that of a gasoline pool ﬁre of the same size.
There are also non-ﬂammable hazards in LNG facilities due
to the presence of refrigerants and other chemicals used
in the gas treatment process.
It is the job of the facility’s ﬁre and gas detection system
to detect these hazards and take appropriate action.
In the event of loss of LNG containment, the process
facility’s ﬁre and gas detection system must rapidly
identify the hazard and indicate its location. Each hazard
must be assessed and assigned a detection scheme with
appropriate response actions that are documented.
No two LNG facilities are exactly the same. Each conforms
to its local surroundings, and is laid out and customdesigned to meet speciﬁc material, throughput, storage
and transport objectives. However, they use common
technologies and perform similar processes.
There is a direct correlation between the performance of a
ﬁre and gas detection system and:
• The appropriateness of the detection
• The number and location of the detectors
• Environmental conditions
Determining which types of detectors to use and where
to place them requires a review of the process and the
hazards presented, as well as ﬁre and gas detection
In order for a system to be designed appropriately, system
performance must be clearly deﬁned and documented in
terms of the hazards present in each process unit (or zone).
The required coverage of hazards by a ﬂame and gas
detection system needs to be speciﬁed. This should
include specifying the appropriate technology for the
detection of the hazard and the required coverage of
each hazard. For example, infrared (IR) gas detectors will
not detect hydrogen sulﬁde. The correct mechanical and
electrical properties of the detectors must also be carefully
selected to ensure that they are appropriate for use in the
environment and location in which they are to be mounted.
3D models help document a ﬁre and gas system design,
and provide calculations for the coverage afforded by
a particular detection scheme to ensure that coverage
targets are attained. 3D mapping is also valuable for
showing individual detectors’ obstructed ﬁelds of view.
(See Figure 1.)
Reliable detection without false alarms
A detector with a greater detection range is generally
considered an advantage, since it means greater ability to
detect the hazard either earlier or from greater distances.
However, it is important that the detector does not lead to
an increased incidence of false alarms.
The system may be conﬁgured to automatically initiate
corrective actions, including engaging the emergency
shutdown (ESD) system, when gas or a ﬂame is detected.
However, false alarms that trigger emergency shutdowns
are expensive in terms of cleanup costs, lost revenue, and
time-consuming reviews, paperwork and reporting. In order
to reduce the probability of false alarms and unintended
activations, it is imperative to use a performance-certiﬁed
detection system that provides immunity to false alarm
sources, and is unaffected by electromagnetic interference
(EMI) and radio-frequency interference (RFI). This is
especially important when a facility uses electrical drives.
Figure 2: Covering a hazard area with voting detectors can reduce the
probability of alarming in the face of a legitimate threat, particularly
where environmental factors such as wind may be present.
Redundancy and fault tolerance
Redundancy should be considered based upon the
criticality of a component, i.e., the impact of that
component’s failure. For example, a facility may consist
of multiple processing trains, each with its own ﬁre and
gas system. In this case, the loss of one controller—and
therefore one train—may not be that critical. However, a
single ﬁre and gas controller could be managing an entire
facility’s ﬁre and gas detection system. A failure of that
controller could lead to facility-wide loss of production;
therefore, redundancy of this critical component can
increase facility availability.
When redundancy is employed, the wiring for the
redundant components must be carefully analyzed to
remove potential common-mode failures that can be
caused by using common cable or conduit. Diverse
routing of wiring for redundant components will
eliminate these possible points of failure. Redundancy
in the detection wiring scheme (Class A) should also be
considered for the purpose of reducing the impact of lost
In addition to the wiring architecture, there are also many
environmental factors, such as wind or other sources of
air movement, to consider. Environmental factors are even
more critical with a voted detection design. For example,
consider two gas detectors installed ﬁve meters apart in
a zone voted to alarm at 20% LFL/LEL. A larger gas cloud
may be needed to contact both detectors to alarm at a
20% LFL/LEL level in a typical outdoor environment.
(See Figure 2.)
Figure 1: 3D mapping can be used to show obstructions in an individual
detector’s ﬁeld of view.
Figure 3: A simpliﬁed LNG process
Selecting detector types in an LNG process
There are different hazards throughout the LNG process
that require different detectors and/or technologies.
Figure 3 depicts the detector types suggested at each
stage in the liquefaction process. In addition to the need
for ﬂame and gas detection throughout the liquefaction
stages, detectors are also needed in other LNG facility
hazard zones, such as storage tank process areas, crosssite transfer trenches and emergency impounding basins.
(See Figure 4.)
The process starts with sour natural gas. As the sour gas
passes through the inlet pipes, it enters the inlet scrubber,
which removes particulate and liquid contaminants in
order to make the gas suitable for further processing. The
gas then moves on to the acid gas unit where hydrogen
sulﬁde (H2S) and CO2 are removed.
Since H2S is particularly poisonous and ﬂammable,
toxic gas detectors are located in this area as well as IR
detectors for natural gas (NG). The gas then moves on to
the dehydration stage. With the H2S removed, detectors in
this area are looking only for NG leaks.
The ﬁnal liquefaction stage is the refrigeration of the gas.
The gas goes through a series of compression and cooling
steps that ultimately create the LNG. There are many
potential leak points and ignition sources in this area of
an LNG facility. Here, point and line-of-sight (open-path)
IR gas detectors are conﬁgured to identify the spectral
signature of the processor’s refrigerant gases—propane,
ethylene or methane. If the hazard is a refrigerant gas
composed of a mixture of gases, then a careful review of
the mixture should be made in order to determine what
the IR gas detectors should be conﬁgured to detect.
In the ﬁnal refrigeration step, the chilled gas enters
the cold box to be transformed into liqueﬁed natural
gas (LNG). From this point forward, IR gas detectors
are conﬁgured to look speciﬁcally for methane leaks.
Additional IR gas detectors are placed along the
piping as the LNG is transferred to storage tanks, and
then ﬁnally onto loading racks or jetties for shipment.
In addition to gas detection, it is also imperative to
detect ﬂame hazards throughout the LNG process.
The multispectrum infrared (MSIR) ﬂame detector
offers optimum performance for this purpose in an
Control and integration
Any effective ﬁre and gas detection and suppression
system must be capable of interfacing with and
integrating ﬂame, gas and smoke detectors, ﬁre
suppression devices and notiﬁcation appliances.
The ﬁre/gas and suppression control system must
be able to:
• Reliably detect hazards and provide appropriate
audible and visual alarms and location of each hazard
• Be available during all plant conditions, e.g.,
plant shutdowns, turnarounds, maintenance
• Integrate seamlessly to other plant control systems,
which provide control of mitigation actions such as
starting water pumps, opening deluge valves and closing
heating, ventilating and air conditioning inlet dampers
• Route digital outputs to the emergency shutdown
system in order to isolate and shut down process
The controller must also be able to handle voting logic
and support user logic that allows the correct actions
to be taken to mitigate the detected event.
The Eagle Quantum Premier® (EQP) ﬁre- and gas-safety
controller by Det-Tronics is one such platform. The EQP
provides access to the local operator network (LON) and
empowers the operator to conﬁgure, program, monitor,
diagnose and control the entire system from a single
point of control.
When designing a ﬁre and gas system in any region of the
world, the designer needs to know and understand the
applicable code and standards. However, some codes and
standards must be followed because they are legislated, such
Figure 4: Ofﬂoading and storage areas in LNG facilities also require
coverage by ﬂame and gas detectors. The diagrams depict three typical
hazard zones: an emergency impounding basin, the storage tank
process area and a cross-site transfer trench.
as ﬁre codes or hazardous locations standards. Using codes
and standards for system design and as criteria for evaluating
product performance will meet the minimum requirements
for what is considered good engineering practice.
In the U.S., the National Fire Protection Association has
published NFPA 59A, a legislated document that governs
the design of LNG facilities. In turn, NFPA 59A requires
that ﬁre systems be in accordance with NFPA 72, The
National Fire Alarm and Signaling Code. In Canada, CSA
Z276-15 (NFPA 59A equivalent) does the same.
In Europe, some of the EN 54 (Fire Detection & Alarm
Systems) series of standards are harmonized under the
Construction Products Regulation, which covers the
essential health and safety requirements for buildings.
Other regions may have their own codes and regulations
that must be followed to be in compliance.
Below are some codes and standards that may be
applicable to the design of a ﬁre and gas system, or are
used in the certiﬁcation of gas or ﬂame detectors.
Systems level standards:
• EN/IEC 60079-29-1,2 series for
• IEC61508 Safety Instrumented Systems
• U.S. — NFPA 72
• Europe — EN 54-2
Gas performance standards:
• U.S. — FM 6310 and FM 6324
• Europe/International — EN/IEC 60079-29 -1,2
Flame performance standards:
• U.S. — FM 3260
As mentioned above, codes and standards are country
speciﬁc. It is the designer’s responsibility to ensure that
selected ﬁre and gas systems and detectors are suitably
approved for the jurisdiction in which they are to be
used. Given the complexity of standards and variations in
their interpretation, LNG plant managers and engineers
typically consult experts in the ﬁeld to help them
through ﬁre and gas detection and suppression system
design, implementation and management. Det-Tronics
provides site analysis, 3D mapping and all the detection
technologies and controls needed for complete ﬂame and
gas detection systems in LNG processing, ofﬂoading and
For a complete explanation of the certiﬁcation and
functional safety approval process, refer to the Det-Tronics
white paper titled, “Why Functional Safety Product Certiﬁers
Must Meet Highest Level of Accreditation.”
• Europe — EN 54-10
DETECTOR TYPES AND CONTROLLERS USED IN LNG APPLICATIONS
Multispectrum infrared (MSIR)
Multispectrum IR ﬂame detectors are often
preferred in LNG environments since background
IR noise is quite common, and this interference
tends to desensitize single-spectrum detectors that are set to detect
one speciﬁc wavelength somewhere between one and ﬁve microns.
MSIR detectors use multiple-IR sensors, each set to detect a different
wavelength, along with processing algorithms that can differentiate
ﬂames from background IR radiation. MSIR detectors vary widely with
respect to the sensitivity range and FOV they provide. For example,
adequately covering a particular hazard zone using detectors with a
range of 50 feet requires six times as many detectors as covering the
same zone using detectors with a range of 200 feet.
Fixed-point toxic gas detectors
Fixed-point toxic gas detectors detect toxic gases
using electrochemical or NTMOS technology.
They measure the concentration at the point
where the detector is located and give readings as
parts per million (PPM). Toxic gas detectors are placed anywhere there
is a potential for a H2S leak hazard.
Fixed-point combustible gas detectors
Fixed-point combustible gas detectors detect
combustible gases using catalytic or infrared
technology. They measure the concentration at
the point where the detector is located and give
readings as the percentage of the lower ﬂammable/explosive limit
(LFL/LEL). Combustible gas detectors monitor for potential ﬂammable
gas leak conditions.
Line-of-sight (LOS) gas detectors
Line-of-sight gas detectors continuously
monitor combustible gas levels between two
points at ranges of up to 120 meters. Lineof-sight detectors are often deployed in and
around open areas and harsh environments that
are typical of an industrial site. This technology is perfect for perimeter
monitoring for gas clouds, and it augments point detectors for optimal
coverage in large open areas.
Acoustic gas leak detectors
Acoustic detectors are non-contact gas leak
detectors that recognize unique acoustic
“ﬁngerprints,” and are ideal for areas where
there is risk for pressurized gas leaks. These
detectors are suitable for harsh outdoor
applications, unmanned operations and extreme temperatures. They
are unaffected by fog, rain, and wind. The ideal acoustic detector
accurately identiﬁes the sound of a gas leak while ignoring other
nuisance environmental sounds.
Certiﬁed systems for detection
Controllers for functional safety systems provide
conﬁgurable and ﬂexible operation for ﬂame
and/or gas detection, alarm signaling, notiﬁcation, extinguishing agent
release and/or deluge operation. It is important that the control platform
is certiﬁed to all applicable standards by a qualiﬁed certifying group(s).
To increase the probability of detection of a hydrocarbon gas leak,
multiple gas detector technologies should be used. (See Figure 5.)
Figure 5: Employing different gas detection
technologies can increase coverage and
reduce risk in high-hazard environments
such as LNG processing facilities.
A ﬁnal word
Producing, storing and transporting LNG is a multifaceted
process with numerous volatile operations and hazards.
Designing a comprehensive and effective ﬁre and gas
detection and mitigation system to protect an LNG plant is
equally complex, requiring thorough analysis and planning.
Requirements have to be carefully assessed, sites have
to be surveyed and mapped out, and appropriate devices
have to be placed, tested and integrated into the detection
and suppression network. The system and its components
must adhere to the relevant local standards, and be
approved by the local accredited certifying organizations
such as FM Approvals.
Implementing such a system is a major undertaking,
and is typically a team effort involving the owners and
managers of the facility, third-party consultants, and
device manufacturer experts such as Det-Tronics.
Det-Tronics is the global leader in ﬁre and gas
safety systems, providing premium ﬂame and
gas detection and hazard-mitigation systems for
high-risk processes and industrial operations.
The company designs, builds, tests and
commissions a complete line of SIL 2 Capable,
globally certiﬁed ﬂame, gas and smoke safety
products, including the X3301 Multispectrum
Infrared Flame Detector and the Eagle Quantum
Premier® (EQP) Fire and Gas Safety Controller.
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