Toxic Atmospheres

Toxic materials, such as vapours, gases, dusts, mists, and fumes, can also contaminate the atmosphere in a confined space. There are many kinds of materials that are toxic, and the ones you may encounter will be different depending on the workplace and industry.

An atmosphere is considered toxic if the levels of toxic materials in the air exceed the exposure limit.

IMPORTANT: Always know what you are working with!

The exposure limit of a toxic substance is defined as the amount of the material in the air to which most people can be exposed without experiencing harmful effects. These limits are most often expressed as a time-weighted average (TWA), which is the exposure averaged over an eight-hour shift. However, you may experience unpleasant side effects, such as coughing, eye irritation, and foul odors, before the exposure limit of a material has been reached. Therefore, it is possible for a worker to suffer health effects from exposure to a toxic substance at lower levels than the defined exposure limit.

Toxic substances can get into confined spaces in a variety of ways, including the following:

• Bacteria can give off toxic gases as a form of decomposition; this happens in sewers or manure pits where methane or hydrogen sulfide is produced and oxygen is used up.
• Toxic materials are stored in, or leak into, the confined space.
• Toxic emissions can come from work being performed in the space. For example, solvents from spray painting or cleaning and degreasing work can contaminate the atmosphere.
• Work in areas close to or connected to the space can be the source of toxic emissions. For example, a vehicle idling near the air intake for an exhaust system or metal fumes from cutting and welding operations can contaminate the space.

To learn more about Firefighter Confined Space visit our Firefighter Confined Space Entry & Rescue Online Training web page.