Twelve-Foot Vault: Alternate Entry or Permit?
A municipal water utility must replace a corroded valve inside a 12-foot-deep below-grade concrete vault at a pump station. The vault has a 30-inch top opening, a fixed ladder, and a sump that historically collects sludge. Entry is expected to last 90 minutes and requires welding on the valve body. Pre-entry readings taken from the top opening read oxygen 20.7%, LEL 0%, hydrogen sulfide 0 ppm, and carbon monoxide 0 ppm. The vault has a permanently installed blower rated at 500 cfm, but the utility's written confined space program predates the current equipment and the last entry permit on file is two years old. The crew of three includes one entrant trained 18 months ago and an attendant who has never performed a rescue. The contractor's rescue plan reads 'call 911.'
1. Can this entry proceed under the alternate-entry procedure, or must it be run under a full permit? Explain your reasoning.
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It must run under a full permit. The alternate-entry provisions of 29 CFR 1910.146(c)(5) apply only when the sole hazard is atmospheric and continuous forced ventilation alone is expected to control it, with pre-entry and continuous monitoring and a documented determination that the space is safe for alternate entry.
Three facts defeat that here. First, welding inside introduces fume, heat, and an ignition source, so the atmospheric hazard is not the only one and dilution ventilation alone is not a complete control. Second, the sump collects sludge that can generate hydrogen sulfide and displace oxygen, so the atmosphere is not reliably controlled by ventilation if the sludge is disturbed. Third, the readings were taken only at the top opening. Hydrogen sulfide is heavier than air and will stratify; a clean reading at the rim says almost nothing about the bottom of a 12-foot vault. Sample from outside at multiple depths (for example every four feet) before entry, and continuously while occupied. Confirm the 500 cfm blower actually delivers air to the bottom rather than short-circuiting across the opening.
2. Evaluate the rescue and attendant arrangements. What must change before anyone enters?
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'Call 911' is a notification, not a rescue plan. 1910.146(k) requires the employer to evaluate the prospective rescue service's ability to respond in a timely manner, confirm it can perform non-entry rescue and, if needed, entry rescue, and provide it with the information it needs: space configuration, hazards, access, and entry point. A municipal department 12 minutes away with no confined-space equipment or training cannot be presumed capable, and no documented evaluation exists.
The attendant who has never been trained in rescue cannot be relied on to perform non-entry retrieval. The attendant must be trained in the duties in 1910.146(i), maintain an accurate count of entrants, summon help, and never enter. Provide a retrieval system (tripod, harness, lifeline) for the entrant, a communication method, a means to summon EMS without leaving the post, and a standby rescue team either on site or under a written mutual-aid arrangement that has been verified, not assumed. If rescue capability cannot be established, the entry does not proceed; there is no compliant path that skips this.
3. List the actions and permit content required before entry, and note any documentation retention requirement.
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Program and permit actions before entry: revise the confined space program so it reflects current equipment and the vault's actual hazard evaluation; issue a permit that records multi-level atmospheric results with instrument type and calibration date, ventilation rate and placement, communication method, and rescue arrangements; designate a competent entry supervisor; verify airflow at the bottom of the vault; issue a hot-work permit with a fire watch for the welding; assign a trained attendant and confirm rescue capability in writing; and confirm entrant training matches assigned duties, retraining when duties or hazards change.
Equipment: 4-gas monitors with alarm setpoints, retrieval system, intrinsically safe lighting, and ventilation rated for the space volume.
Brief the crew on emergency signals and evacuation before the first entry, post the permit at the entry point, and retain the completed permit for at least one year (1910.146(e)(6)). Also confirm whether the utility's state plan or local rules add requirements, and whether the vault must be treated as a permit space under the site's own hazard evaluation regardless of the contractor's opinion.