Confined Space Entry for a Below-Grade Sewer Repair
A crew must repair a broken 6-inch sewer line inside a 5-foot-deep, 4-foot-diameter concrete manhole in a parking lot. The manhole has one 24-inch access opening. Ambient temperature is 30 degrees C. A gas monitor clipped to the attendant's belt reads 0 percent LEL, 20.9 percent oxygen, and 0 ppm H2S before entry. The crew plans to lower a worker on a tripod and lifeline to make the repair, which will take about 45 minutes. There is no mechanical ventilation on site. The worker mentions feeling lightheaded after a previous similar job. A second worker is available to act as attendant. You must decide whether entry can proceed and what controls are required.
1. Is this a permit-required confined space, and can entry proceed based on the initial readings?
Read the worked answer
Yes, it is a permit-required confined space: it is large enough to enter, has limited entry (one 24-inch opening), and is not designed for continuous occupancy. Sewer lines can generate H2S, methane, and oxygen deficiency, so it is also a hazardous atmosphere space.
Initial readings alone do not authorize entry. The meter was clipped to the attendant at the top, not lowered to the worker's breathing zone at the bottom. Readings must be taken at the bottom and at multiple depths before and during entry. The prior lightheadedness suggests possible H2S exposure or oxygen displacement and must be treated as a red flag.
Entry cannot proceed on the current readings; pre-entry testing at the work elevation is required.
2. List the controls required before and during the 45-minute entry.
Read the worked answer
Required controls:
- Written entry permit signed by the entry supervisor.
- Pre-entry and continuous atmospheric monitoring at the bottom and breathing zone (O2, LEL, H2S, CO).
- Forced-air ventilation for the duration, since sewer gas can accumulate and the space is not naturally ventilated.
- Attendant stationed at the opening with a retrieval system (tripod and lifeline) rigged and attended.
- Communication between entrant and attendant (voice or radio).
- Personal gas monitor on the entrant, plus a backup meter.
- Rescue plan and trained rescue personnel; non-entry rescue preferred.
- Isolate the sewer flow (plug or bypass) to prevent flooding and gas generation.
If ventilation cannot maintain safe levels, entry must be aborted. The 45-minute duration and heat (30 C) also require attention to heat stress and hydration.