The "OFT" Order of Testing
Always test for atmospheric hazards in the following order:
- 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. In addition, both oxygen-deficient and oxygen-enriched atmospheres are extremely hazardous to workers' health and safety. Oxygen levels should be between 19.5% - 23.5%.
- Flammable or explosive gases and vapors 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)
- 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).
Atmosphere Sampling Procedure
The atmosphere of a confined space should be analyzed using equipment of sufficient sensitivity and specificity to identify and evaluate any hazardous atmospheres that may exist or arise, so that appropriate permit entry procedures can be developed and acceptable entry conditions stipulated for that space.
Evaluation and interpretation of this data, and development of the entry procedure, should be done by, or reviewed by, a technically qualified professional (e.g., OSHA consultation service, or certified industrial hygienist, registered safety engineer, certified safety professional, certified marine chemist, etc.) based on evaluation of all serious hazards.
The atmosphere of a permit space should be tested for residues of all contaminants identified by evaluation testing to determine that residual concentrations at the time of testing and entry are within the range of acceptable entry conditions.
When monitoring for entries involving a descent into atmospheres that may be stratified, the atmospheric envelope should be tested a distance of approximately 4 feet (1.22 m) in the direction of travel and to each side. If a sampling probe is used, the entrant's rate of progress should be slowed to accommodate the sampling speed and detector response.
Results of testing (i.e., actual concentration, etc.) should be recorded on the permit in the space provided adjacent to the stipulated acceptable entry condition.
If entrants leave the confined space for any reason, they should once again test the atmosphere within confined spaces because it can change rapidly.
Test results that show the composition of an atmosphere to which employees are actually exposed (even if the employees are using respirators) must be available so that they can be reviewed by members of the entry team or representatives.
Knowledge Check Choose the best answer for the question.
4-9. Oxygen levels in a confined space should be maintained _____.
You forgot to answer the question!