Nitrogen or other non-life supporting gases such as carbon dioxide often are used to back up instrument air to ensure a reliable supply. If the instrument air is used to supply breathing air for maintenance activities or if the instrument air is used for other purposes such as operating pneumatic tools in confined or poorly ventilated spaces, the individuals involved could be asphyxiated if the back-up system is activated and the non-life supporting gas replaces the air.

Instrument air is easily mistaken for breathing air and is considered innocuous because of its name. It is often referred to in conversations in plant surroundings as “instrument air” and it could be labeled as such. Similarly, the names “plant air,” “shop air,” “utility air,” and “compressed air” all suggest that the “air” contains the normal amount of oxygen found in the atmosphere. Contractors doing maintenance work can be particularly at risk for asphyxiation since they might not be familiar with the plant site or the source of the instrument gas.

This publication provides methods to avoid asphyxiation caused by the accidental use of a non-life supporting gas in place of instrument air.