Test a Permit Space in the Order OSHA 1910.146 Requires

Before anyone enters a permit-required confined space, OSHA 29 CFR 1910.146(d)(5)(i) requires the employer to test conditions in the space to determine whether acceptable entry conditions exist. Paragraph (d)(5)(iii) sets the order of atmospheric tests. A 4-gas monitor with a sampling pump covers all three steps from outside the space.

Test oxygen first, then flammables, then toxics

1910.146(d)(5)(iii) states: test first for oxygen, then for combustible gases and vapors, and then for toxic gases and vapors. Paragraph (c)(5)(ii)(C), for spaces entered under the alternate procedures, uses the same order and requires a calibrated direct-reading instrument.

Oxygen comes first because most combustible gas sensors need oxygen to read correctly, and an oxygen-deficient atmosphere is the most immediate threat to the entrant. Combustibles come next because a flammable atmosphere threatens everyone at the opening, not only the entrant.

Sample the whole space from outside.

• Use a pump and probe or tubing so the person testing remains outside the space.
• Test at several levels. Gases lighter than air collect near the top, and heavier gases settle near the bottom.
• Allow the pump enough time to draw the sample through the full length of tubing before you read the display. The manufacturer’s instructions give the time.

The gas monitor comparison includes a meter with a 0.5 LPM external pump and a stainless probe, as well as a lower-cost pumped unit.

Let the entrant observe the test

1910.146(d)(5)(iv) requires the employer to provide each authorized entrant, or that employee’s authorized representative, with an opportunity to observe the pre-entry testing and any subsequent testing. Paragraph (d)(5)(v) requires the employer to reevaluate the space in the presence of an entrant or representative who requests it when there is reason to believe the evaluation was inadequate.

Keep monitoring during entry

1910.146(d)(5)(ii) requires testing or monitoring of the space as necessary to determine whether acceptable entry conditions are maintained during entry operations. A diffusion monitor worn by each entrant provides continuous readings once the space is cleared. Record the results on the entry permit, as 1910.146(f)(10) requires the permit to list the results of initial and periodic tests, the testers' names or initials, and the time.

Act on a reading above the limits

If any reading falls outside acceptable entry conditions, no one enters until the hazard is controlled. Ventilate, isolate the source, and retest in that order. If the atmosphere changes during entry, 1910.146(d)(5)(ii) monitoring detects it. Under 1910.146(i)(6), the attendant orders the entrants to evacuate, and under (e)(5), the entry supervisor terminates entry and cancels the permit. The permit lists the acceptable entry conditions, so the attendant and entrants know the limits before work starts.

Trust the reading only from a working instrument.

• Use a calibrated direct-reading instrument, as (c)(5)(ii)(C) requires for alternate-procedure entries.
• Follow the manufacturer’s schedule for calibration and for a functional check with known gas before use.
• Confirm the instrument has sensors for every toxic gas the space may hold. A 4-gas monitor reads CO and H2S; other contaminants need other sensors.

Clear the space in five steps.

1. Check the instrument and its calibration date.
2. From outside the space, test oxygen.
3. Test combustible gases and vapors as a percentage of the LFL.
4. Test toxic gases at several levels.
5. Record the results on the permit and keep monitoring during entry.

The 4-gas monitor guide compares three monitors across sensors, pump, calibration documentation, and Amazon price.