It is important to note that whereas portable gas detection instruments measure and alarm at the TWA levels, instantaneous alarms are included to provide early warning of an exposure to dangerous gas concentrations. Workers are often under risk of gas exposure in situations where atmospheres cannot be controlled, such as in confined space entry applications where alarming at TWA values would be inappropriate.
You must perform your own risk assessment to ensure alarms are set to appropriate levels for your application and in accordance with local legislation and practices.
The following data has been extracted from EH40 and OSHA for some common toxic gases:
Workplace Exposure Limits:
|WORKPLACE EXPOSURE LIMITS
|SUBSTANCE||CHEMICAL FORMULA||LTEL (8hr TWA) PPM||STEL (15 minute TWA) PPM||LTEL (8hr TWA) PPM|
|Chlorine||Cl2||–||0.5||1 ceiling *|
|Ethylene Oxide ETO||C2H40||5||–||1|
|Hydrogen Chloride||HCI||1||5||5 ceiling*|
|Hydrogen Sulphide||H2S||5||10||20 ceiling*|
|Nitrogen Dioxide||NO2||0.5||1||5 ceiling*|
*C – Ceiling Limit
OSHA (Occupational Safety and Health Administration) Permissible Exposure Limits
EH40/2005 Workplace exposure limits (Third Edition, published 2018)