Application Data Sheet
ADS-001
Gas Sensor Placement Guidelines
Selecting the location for placement of gas sensors involves several different factors. You must first
evaluate the gas risk in the facility. The risk assessment process is critical in both identifying the potential
consequences of a gas leak to personnel, facilities and the environment and establishing the liability to
the firm of a significant leak. Based upon the risk assessment you can decide what sensors are required.
Second, you must evaluate the physical location to determine the number of sensors required and their
placement.
Qualification:
The guidelines presented below are for
reference only. They are not exhaustive
and should not be substituted for a
professional analysis of the gas risk
·
Dilution rates and convection currents (as
affected by natural diffusion, forced air
ventilation procedure, etc.)
problem.
These guidelines do not
·
·
Density of gas (heavier or lighter than air
– see Chart 1)
address related subjects such as a
comprehensive hazard assessment, data
logging, system operation, system alarm
response and alarm procedures at the
facility.
Interfering gases
A. Use engineering judgment
Chart 1: Gas Weight in Relation to Air for
Typical Gases
There are no complete and definitive
regulations or guidelines published by
ISA, NFPA, UL, FM or other agencies that
tell users where or how many gas sensors
to use. 1 Each gas leak possibility must be
evaluated as a unique problem to assess
the risk to people and property. The
object of monitoring system design is to
reduce the risk to people and property by
responding to the gas leak.
Ammonia
Lighter
Butane
Heavier
Carbon Dioxide
Carbon Monoxide
Methane
Heavier
Slightly Lighter
Lighter
Chlorine
Heavier
Ethane
Slightly Heavier
Slightly Lighter
Heavier
Note 1: NFPA has published NFPA 73E
Standard on Automatic Fire Detectors,
Appendix A, which suggest that a diffusion
sensor used for smoke detection be
placed every 900 square feet of ceiling
space.
Ethylene
Heptane
Hydrogen
Lighter
Hydrogen Chloride
Hydrogen Cyanide
Hydrogen Sulfide
Methyl Alcohol
Nitric Oxide
Nitrogen Dioxide
Pentane
Heavier
Lighter
B. Consider
Heavier
Heavier
·
Probability of gas leaks (i.e.
equipment
or
material
failure,
Slightly Heavier
Heavier
operating
error,
changes
in
composition of materials used, etc.)
Heavier
·
·
Quantity of gas that could be present
Propane
Heavier
Sulfur Dioxide
Toluene
Heavier
Environmental conditions (i.e. wind
speed, wind direction, blowers/fans in
room, temperature, etc.
Heavier
Sierra Monitor Corporation 1991 Tarob Court Milpitas, California 95035 (408) 262-6611 (800) 727-4377 fax: (408) 262-9042
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