Unresponsive Worker in a Sewer Wet Well
At 14:20 a municipal utility requests rescue for a worker collapsed at the bottom of a 4.5 m deep, 1.2 m diameter sewer wet well. The well has a fixed ladder, a 60 cm top hatch, and a 30 cm intake pipe. The worker is unresponsive, partly in 30 cm of wastewater, and is not wearing a retrieval harness. The attendant's readings at the hatch are O2 19.3%, LEL 12%, H2S 42 ppm, and CO 8 ppm. The well is permit-required. The rescue team has a tripod, 30 m of rope, a Class III harness, SCBA with 30-minute cylinders, a supplied-air respirator with a 15-minute escape cylinder, one calibrated four-gas meter, and a 20 cm ventilation duct with a fan 15 m away. The team consists of two confined-space technicians, one paramedic, and one attendant. Ambient temperature is 30°C. Additional fire department resources are 12 minutes away.
1. What is the rescue mode and what atmospheric and equipment conditions must be met before entry?
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Treat this as a rescue, not a recovery, because the patient was working minutes ago and may still be alive. That does not authorize an unprotected entry. The readings show O2 19.3%, below the 19.5% entry threshold; LEL 12%, above the 10% limit; and H2S 42 ppm, above the short-term exposure limit and high enough to cause rapid incapacitation at higher concentrations. CO is 8 ppm. Entry requires positive-pressure SCBA or supplied air with an escape cylinder, intrinsically safe monitoring, and continuous ventilation.
Before entry, confirm isolation with lockout/tagout or blanking, set continuous four-gas monitoring at the top, middle, and bottom, start ventilation with the fan intake in clean air, and establish two entry rescuers plus an attendant and a backup team. The single meter is a limitation: bump-test it, use it continuously, and request a backup meter. Eliminate ignition sources around methane. The ladder is wet and contaminated, so plan a rope descent rather than relying on it.
2. How do you rig and conduct the entry given the victim has no harness and the hatch is only 60 cm?
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Set the tripod over the hatch and rig a mainline for the rescuer with a descending device and a separate belay. The 60 cm hatch is too small for a rigid litter, so plan on a rescue harness or flexible stretcher for the victim. The rescuer descends on rope, not the ladder, because the ladder is wet and contaminated. The rescuer wears SCBA and a harness with a retrieval line; the attendant tends both lines and monitors the meter.
At the bottom, the rescuer checks responsiveness and airway, then places a rescue harness on the victim. If the victim is face-down in wastewater, move them out of the water first and begin airway care. Attach the victim to a separate retrieval line with a 3:1 or 4:1 mechanical advantage if needed. Do not attach the victim to the rescuer's mainline; use an independent high point or a separate line over the hatch with edge protection. Two rescuers should be available at the top to lift. Keep continuous communication and monitor H2S at the bottom.
3. After 5 minutes of ventilation the bottom reading is H2S 85 ppm and LEL 18%. The victim is still unresponsive. What decision and actions?
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Stop entry. H2S at 85 ppm is approaching the IDLH of 100 ppm and can cause rapid loss of consciousness; LEL 18% is nearly twice the 10% entry limit and is an explosion hazard. Withdraw all personnel from the well and the immediate area. Move the fan intake to clean air and check that the fan is non-sparking; if the LEL is rising, ventilation may be mixing a pocket or the source is still feeding the space. Eliminate ignition sources and request hazmat and additional confined-space teams.
Rescue from outside is still possible only if a line can be placed on the victim without entry; the victim has no harness. Do not send a rescuer into an atmosphere above IDLH without supplied air and a backup plan. If entry is absolutely necessary, it must be with SCBA, intrinsically safe equipment, two rescuers, and a standby team, but the current readings make that a high-risk last resort. Keep the rescue posture while the atmosphere is controlled, but do not let urgency create a second victim.