Atmospheric testing procedures

Evaluation testing and verification testing serve two different purposes: evaluation testing identifies and characterizes potential hazardous atmospheres so you can develop the entry procedure, while verification testing confirms that the concentrations at the time of entry are within the acceptable entry conditions.

• Evaluation testing uses "equipment of sufficient sensitivity and specificity" to identify and evaluate hazards so that appropriate permit procedures and acceptable entry conditions can be developed; this work should be done or reviewed by a "technically qualified professional" (examples are given in the appendix). See 1910.146AppB.
• Verification testing uses the permit-specified equipment to test for residues of all contaminants identified by the evaluation and to determine that residual concentrations at the time of testing and entry are within the stipulated acceptable entry conditions; the results should be recorded on the permit. See 1910.146AppB.

A technically qualified professional should evaluate the data and develop or review the permit entry procedure.

• The appendix explicitly recommends that evaluation, interpretation of atmospheric data, and development of the entry procedure be done by or reviewed by a "technically qualified professional" such as an OSHA consultation service, certified industrial hygienist (CIH), registered safety engineer, certified safety professional (CSP), or certified marine chemist. See 1910.146AppB.

You should use instruments that have sufficient sensitivity and specificity to identify and evaluate any hazardous atmospheres that may exist or arise in the space.

• The appendix requires "equipment of sufficient sensitivity and specificity" so the instruments can reliably detect the hazardous atmospheres you expect; choose sensors that can detect the contaminants and concentration ranges identified during the hazard evaluation. See 1910.146AppB.
• When in doubt, involve a technically qualified professional to select or confirm instrument suitability as recommended in 1910.146AppB.

You must measure each atmospheric parameter for at least the instrument manufacturer's minimum response time for that device.

• The appendix states that measurement "should be made for at least the minimum response time of the test instrument specified by the manufacturer," so check the instrument manual or data sheet and allow that minimum sampling/response period for each parameter. See 1910.146AppB.

You should test for oxygen first, then combustible gases, and perform tests for toxic gases and vapors last.

• The appendix explains the order: oxygen is tested first because most combustible gas meters are oxygen dependent and will not give reliable readings in an oxygen-deficient atmosphere; combustible gases next because fire/explosion is often the most immediate life threat; and toxic gases last. See 1910.146AppB.
• For oxygen-deficient concerns, also see OSHA’s interpretation on oxygen-deficient atmospheres which discusses how OSHA treats oxygen-deficient conditions as immediately dangerous to life and health and the need to consider such conditions in planning monitoring and protection: https://www.osha.gov/laws-regs/standardinterpretations/2024-07-16.

You should test the atmospheric envelope about 4 feet (1.22 m) ahead in the direction of travel and to each side before descending, and slow the entrant if a sampling probe is used to accommodate sampling speed and detector response.

• The appendix instructs that when monitoring for entries involving a descent into potentially stratified atmospheres, the atmosphere should be tested a distance of approximately 4 feet 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 probe's sampling speed and the detector response. See 1910.146AppB.

You should record the actual test results (for example, actual concentrations) on the permit in the space provided adjacent to the stipulated acceptable entry condition.

• The appendix states that results of verification testing (i.e., actual concentration, etc.) "should be recorded on the permit in the space provided adjacent to the stipulated acceptable entry condition," so include the numeric readings, the time, the instrument used (if useful), and any notes about conditions at the time of testing. See 1910.146AppB.

Verification testing must test for residues of all contaminants identified during the earlier evaluation testing using the permit-specified equipment.

• The appendix requires that the atmosphere of a permit space which may contain a hazardous atmosphere "should be tested for residues of all contaminants identified by evaluation testing" to determine that residual concentrations at time of testing and entry are within acceptable entry conditions. See 1910.146AppB.

Yes—provided the instrument meets the needs of each phase: it must have the sensitivity and specificity required for evaluation testing and be the permit-specified equipment for verification testing.

• The appendix distinguishes the two purposes (evaluation versus verification) but does not forbid using the same device; it requires that evaluation use instruments with sufficient sensitivity/specificity and that verification use the permit-specified equipment. If one instrument meets both requirements and is approved in the entry permit, it can serve both roles. See 1910.146AppB.

Because most combustible gas meters are oxygen dependent and will not give reliable readings in oxygen-deficient atmospheres, oxygen must be checked first.

• The appendix explicitly requires oxygen testing first because combustible-gas meters often rely on oxygen to function and can give unreliable readings if oxygen is deficient; this order also reflects the immediate life/safety priorities—oxygen and fire/explosion risks. See 1910.146AppB.
• For guidance on recognizing oxygen-deficient atmospheres as immediately dangerous to life and health (IDLH) and treating them accordingly in protection plans, see OSHA’s interpretation on oxygen-deficient atmospheres: https://www.osha.gov/laws-regs/standardinterpretations/2024-07-16.

You should slow the entrant's rate of progress so that the sampling probe and detector have time to sample and respond before the entrant moves into the next area.

• The appendix advises that if a sampling probe is used, the entrant's rate of progress should be slowed to accommodate the sampling speed and detector response. Practically, this means pause at sampling locations long enough for the instrument to reach its minimum response reading and for the probe to collect a representative sample. See 1910.146AppB.

The "minimum response time" is the shortest period the manufacturer specifies that the instrument needs to sense and report an accurate reading, and you should measure each parameter for at least that time.

• The appendix directs users to make measurements "for at least the minimum response time of the test instrument specified by the manufacturer," so consult the instrument's user manual or manufacturer datasheet for that response time and follow it during testing. See 1910.146AppB.

Tests for toxic gases and vapors should be performed after testing for oxygen and combustible gases.

• The appendix instructs that oxygen testing is performed first, combustible gases next, and toxic gases and vapors are performed last. This order addresses instrument limitations and immediate life-safety priorities. See 1910.146AppB.

If oxygen is low and the combustible gas meter reads no gas, treat the atmosphere as potentially hazardous and rely on oxygen measurement and qualified evaluation before trusting combustible readings.

• The appendix warns that most combustible gas meters are oxygen dependent and will not provide reliable readings in an oxygen-deficient atmosphere; therefore a zero combustible reading in a low-oxygen environment may be unreliable and you should not assume the space is safe. See 1910.146AppB.
• Also consult OSHA’s guidance on oxygen-deficient atmospheres which treats low-oxygen conditions as immediately dangerous to life and health and requires appropriate protective measures and evaluation: https://www.osha.gov/laws-regs/standardinterpretations/2024-07-16.