Atmospheric & Gas Hazards

 Oxygen-deficient atmospheres (< 19.5%) O2 where you can easily pass out may be created when oxygen is displaced by other gases, such as carbon dioxide, nitrogen, argon, or firefighting system. Oxygen can also be consumed by rusting metal, ripening fruits, drying paint, or coatings, combustion, or bacterial activities. Oxygen-enriched atmospheres (> 22%) present a fire and/or explosion hazard.

The Lower explosive limit (LEL) of a combustible gas is the minimum concentration of vapor in air below which propagation of a flame does not occur in the presence of an ignition source. 

 Carbon Monoxide (CO) is often called the Silent Killer as it is undetectable by humans so you need an instrument. It's a debilitating, cumulative poison meaning exposure level and time of exposure both factor in. 

 Hydrogen Sulfide (H2S) exposure can cause debilitating respiratory effects as it can make “acid” in your lungs. Most people can smell low levels (<2 ppm, rotten egg smell), but the nose is not a reliable sensor.