Test with Caution

Toxic gases can be heavier than normal air, and confined spaces have poor air circulation. This means that the gases can form layers at different heights in the space. Therefore, test for gases from top to bottom as well as from side to side in case there are pockets of stagnant gases.

To avoid exposure to toxic gases or explosions from flammable gases, test areas like manholes, vaults, or sewers with caution. First, try to test through "pick holes" in the cover or lid, or open the cover just enough to insert the test probe. If that test shows nothing flammable or toxic, you can then remove the lid or open the manhole and test the space thoroughly.

If working with flammable materials, there can be differences in acceptable levels depending on whether the work is considered "cold work" (no sources of ignition involved) or "hot work" (capable of producing a source of ignition like sparks).

You should check the confined space entry permit for all of the information about the space and delay entry until ALL the hazards have been identified and measured and proper safety precautions have been taken.

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