Confined-Space Entry and Rescue in a Boiler Steam Drum
During a 210 MW boiler overhaul, a contract crew is to inspect the steam drum internally. The drum is 1.8 m diameter, 14 m long, with two 450 mm manholes; volume is about 35 m³. The permit is valid for 2 hours. Initial gas test at the manhole: O2 19.5%, CO 30 ppm, LEL 3%, H2S 1 ppm. Forced ventilation was run for 20 minutes and then switched off to avoid draft. After 40 minutes, the standby person left to fetch a torch. The entrants descended to the bottom of the drum. A second gas test at the bottom is not recorded. Shortly afterwards, one entrant feels dizzy and collapses; the other tries to lift him and also becomes weak. The manhole is 600 mm above the drum bottom, and the rescue tripod is at the far end of the platform.
1. Using the readings and the physical layout, explain why the atmosphere at the drum bottom could be unsafe despite the initial manhole reading. Identify at least three permit violations.
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The manhole reading is not representative of the whole drum. In a 1.8 m drum, heavier gases, rust oxidation and stagnant pockets can create a bottom layer with lower oxygen and higher CO than at the manhole. Switching off ventilation removed dilution, and no bottom or mid-height test was recorded. The collapse pattern - one entrant down, the would-be rescuer weak - is classic oxygen deficiency, not simple fatigue. Permit violations include: ventilation switched off before entry; standby person leaving the manhole; no gas test at the bottom; no continuous monitoring; no retrieval line or harness on entrants; rescue tripod not positioned over the manhole; and a 2-hour permit without revalidation. The 600 mm sill also means a casualty must be lifted vertically, so the tripod position is a real rescue deficiency.
2. State the immediate rescue actions, in order, without entering the drum.
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First raise the alarm and call the site emergency or fire crew. Do not enter without SCBA. Start forced ventilation at the manhole and keep non-essential people away. If the entrant has a harness and retrieval line, use the tripod from outside; if not, do not attempt a blind reach into the drum. Reposition the tripod over the manhole because the 600 mm sill requires a vertical lift. Maintain voice contact if possible. A trained rescue team with SCBA, harness and lifeline should enter only after the atmosphere is tested and controlled. After removal, give oxygen, keep the casualty warm and hand over to medical staff. Preserve the permit and gas-test records for investigation.
3. Recommend changes to the permit and gas-testing regime for the next entry.
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Require continuous mechanical ventilation for the whole entry. Test at top, middle and bottom before entry and at intervals of no more than 30 minutes, or use continuous personal monitors with alarms. Set entry limits such as O2 19.5-23.5%, LEL below 1%, CO below 25 ppm and H2S below 5 ppm, unless the project specifies stricter values. The standby attendant must remain at the manhole with no other duty. Entrants should wear a full-body harness with retrieval line, the tripod should be over the manhole, and a rescue drill should be held before entry. Use an entry log with names and times, and revalidate the permit after any break or alarm.