If H2S readings remain hazardous after initial ventilation, what is the recommended action?

• A. Continue cleaning with extra PPE.
• B. Evacuate and reassess before re-entry.
• C. Ignore the readings and proceed.
• D. Increase ventilation for another hour.

Answer: (B)

When H2S is still hazardous after initial ventilation, the space is not yet safe to re-enter. H2S is extremely toxic and can linger in pockets or stratify in a confined area, so simply venting for a while doesn’t guarantee that every breathing zone is safe. The responsible action is to evacuate the area and reassess conditions before attempting entry again. This gives time to verify with calibrated gas detectors in the breathing zone, confirm that ventilation is effectively reducing concentrations, and ensure a proper rescue plan and standby personnel are in place.

Relying on more PPE or pushing ahead with cleaning until the clock runs out isn’t enough because PPE cannot reliably overcome a hazardous gas in the environment, and dangerous pockets can still exist even with extended ventilation. Ignoring the readings is unsafe. Simply increasing ventilation for another hour without reassessment may still leave you at risk if concentrations remain above safe levels or if pockets re-form.