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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 

 

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