Sierra Monitor Corporation Carbon Monoxide Alarm Gas Sensor User Manual

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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