Gas Detector Alarm Settings

General Gas Education

Gas Detector Alarm Settings PDF






O2 19.5% vol 23.5% vol N/A N/A
CO 35 ppma, b 70 ppmb 35 ppma  200 ppm
H2S 10 ppm 20 ppm 10 ppm 15 ppm
SO2 2.0 ppm 4.0 ppm 2.0 ppm 5.0 ppm
NO2 3.0 ppm 6.0 ppmc 3.0 ppm 5.0 ppm
Cl2 0.5 ppm 1.0 ppm 0.5 ppm 1.0 ppm
ClO2 0.1 ppm 0.2 ppm 0.1 ppm 0.3 ppm
CO2 0.5% vol 1.0% vol 0.5% vol 3.0% vol
PH3 0.3 ppm 0.6 ppm 0.3 ppm 1.0 ppm
NH3 25 ppm 50 ppm 25 ppm 35 ppm
HCN 5.0 ppm 10.0 ppm 4.0 ppm 4.0 ppm
NO 25 ppm 50 ppm 25 ppm 25 ppm
HCl 2.5 ppm 5.0 ppm 2.5 ppm 2.5 ppm
H2 50 ppm 100 ppm N/A N/A
CH4 1.0% vol 1.5% vol N/A N/A
LEL 10% LEL 20% LEL N/A N/A
PID 100 ppm 200 ppm N/A N/A

a. For CO, OSHA PEL is 50 ppm, Industrial Scientific uses the standard set in 1989 (35 ppm). All alarm set points are field adjustable over the full range of the sensor, exceptions: LEL/CH4 – 0 to 60% and 0 to 3.0% by vol CH4. Provided standards exist, all alarm settings are based on the following: Low alarms are based on OSHA PEL and/or NIOSH values. High alarms are based on 2 times OSHA PEL values.

b. MSHA CO limits are 50 ppm for a low alarm and 100 ppm for a high alarm.

c. MSHA NO2 limits are 5 ppm for a high alarm. 

TRAINING DISCLAIMER: These training videos and other training materials are intended to assist employers, workers, and others as they strive to improve workplace health and safety, by educating them on the practical use of Industrial Scientific® gas detection equipment. While we attempt to thoroughly address the specific topics, it is not possible to include discussion of everything in a presentation of this nature. Thus, this information must be understood as a tool to assist you in the operation of your Industrial Scientific® gas detection equipment. Finally, over time, Industrial Scientific Corporation may update the training materials and videos in light of new technology, information, or circumstances; to keep apprised of such developments, or to review a complete and up to date library of our training materials, you can visit our website at or download our app.