Application Data Sheet
ADS-001
Sierra Monitor Corporation 1991 Tarob Court Milpitas, California 95035 (408) 262-6611 (800) 727-4377 fax: (408) 262-9042
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
problem. These guidelines do not
address related subjects such as a
comprehensive hazard assessment, data
logging, system operation, system alarm
response and alarm procedures at the
facility.
A. Use engineering judgment
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.
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.
B. Consider
•
Probability of gas leaks (i.e.
equipment or material failure,
operating error, changes in
composition of materials used, etc.)
•
Quantity of gas that could be present
•
Environmental conditions (i.e. wind
speed, wind direction, blowers/fans in
room, temperature, etc.
•
Dilution rates and convection currents (as
affected by natural diffusion, forced air
ventilation procedure, etc.)
•
Density of gas (heavier or lighter than air
– see Chart 1)
•
Interfering gases
Chart 1: Gas Weight in Relation to Air for
Typical Gases
Ammonia
Lighter
Butane
Heavier
Carbon Dioxide
Heavier
Carbon Monoxide
Slightly Lighter
Methane
Lighter
Chlorine
Heavier
Ethane
Slightly Heavier
Ethylene
Slightly Lighter
Heptane
Heavier
Hydrogen
Lighter
Hydrogen Chloride
Heavier
Hydrogen Cyanide
Lighter
Hydrogen Sulfide
Heavier
Methyl Alcohol
Heavier
Nitric Oxide
Slightly Heavier
Nitrogen Dioxide
Heavier
Pentane
Heavier
Propane
Heavier
Sulfur Dioxide
Heavier
Toluene
Heavier
