Testing for Hazardous Atmospheres
Atmospheric testing is required for two distinct purposes:
- Evaluation of the hazards of the permit space, and
- Verification that acceptable entry conditions for entry into that space exist.
Testing Sequence
As we briefly mentioned in the first module, it's important to use the following sequence when testing for hazardous atmospheres before entry into an actual or potential confined space.
- O - Oxygen is tested first because most combustible gas and toxic atmosphere meters are oxygen-dependent and will not provide reliable readings when used in oxygen-deficient atmospheres. Also, both oxygen-deficient and oxygen-enriched atmospheres are extremely hazardous to workers' health and safety. Oxygen levels should be between 19.5% - 23.5%.
- F - Flammable or explosive atmospheres are tested next because the threat of fire and explosion is both more immediate and more life-threatening, in most cases, than exposure to toxic gases and vapors. Flammability limits should be less than 10% of the Lower Flammability Limit (LFL).
- T - Toxic atmospheres are tested last. Many modern direct-reading instruments provide simultaneous readings of multiple gases. Readings should be less than recognized ACGIH exposure limits or other published exposure levels (e.g. OSHA PELs, NIOSH RELs).
Monitoring for Hazardous Atmospheres
Monitoring is the only way to detect whether a hazardous atmosphere has developed during entry. If this is the case, employees will be alerted to the change so they can leave the space immediately.
Of those contaminants that have odor, some can be detected by our senses only at low concentration. Hydrogen sulfide, for example, will deaden the sense of smell at high concentrations. Because of this, employees might assume that a confined space is safe when it is not. There is no substitute for testing the air in a confined space before entry. A worker can also be exposed to a contaminant through skin contact while working in a confined space. Atmospheric monitoring is necessary whenever:
- A safe atmosphere cannot be ensured.
- An existing hazardous atmosphere cannot be removed.
- The confined space cannot be physically isolated from the penetration of hazardous materials.
- There is reason to suspect the development of a hazardous atmosphere during work activity.
Knowledge Check Choose the best answer for the question.
2-9. Why is oxygen tested first using the O-F-T testing model for initial testing of confined spaces for hazardous atmospheres?
You forgot to answer the question!