Refinery column inspection with rising H2S and a corroded support
You are the Level 3 supervisor at a refinery. The task is external ultrasonic thickness measurement and visual inspection of a 58 m process column with a history of corrosion under insulation. An adjacent line contains sour gas. The permit gas test was at 06:00: 0 ppm H2S and 0% LEL. It is now 13:30, the wind has shifted, and you notice a hydrocarbon odour. The area operator says 'that smell is normal.' Your personal H2S monitor reads 4 ppm and is rising. The team is rigged at 30 m. The rescue plan relies on self-rescue and a radio call. A 180°C steam line runs near the anchor. A technician finds a corroded support bracket with about 30% metal loss and wants to lean around the column to take close-up photographs. The permit is for cold work only.
1. What do you do when the H2S monitor reads 4 ppm and rising?
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Treat it as a gas release until proved otherwise. 4 ppm is above the typical 1–5 ppm alarm threshold and below the immediate danger level, but the trend matters more than the number. Stop work, tell the team to stop, and move upwind/away from the column using the escape route; do not descend through the plume. Account for all personnel at the muster point and notify the control room immediately. Do not rely on the odour: H2S causes olfactory fatigue, and 'normal smell' is not a gas test. The area operator's comment does not override the monitor.
The control room should isolate or identify the source, re-test the area, and declare it safe before re-entry. If anyone has symptoms, seek medical evaluation. The permit must be suspended and revalidated.
2. Is the 06:00 gas test still valid at 13:30? What must happen before re-entry?
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No. A gas test is a snapshot; it is not valid for seven and a half hours, especially with a wind shift and an odour. The permit's gas test has expired by time and by change of conditions. Before re-entry: control the source, re-test at the actual work position rather than only at the access point for H2S and LEL, establish continuous monitoring with personal monitors and alarms, confirm ventilation and wind direction, and revalidate the permit with the area authority. Consider whether the task remains cold work and whether the adjacent sour gas line is the source. If the reading is not low and stable, do not re-enter. The rescue plan must also be revised for a gas exposure rescue, including escape sets and retrieval from height.
3. The technician wants to lean around the column to photograph the corroded bracket. What do you say?
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No, not if it means unclipping, loading the corroded bracket or moving beyond the rigged access without a new risk assessment. The bracket has about 30% metal loss and is not a certified anchor; it may be structurally compromised. Use a camera pole, remote camera or reposition the ropes to get the view without loading the bracket. If close access is essential, treat it as a new task: assess the bracket, add independent anchors, and revise the method statement and permit.
Report the corrosion to the client's engineer promptly; 30% loss on a support may need immediate structural evaluation. Photograph from a safe position and record the location so the client can plan repair. Do not let the inspection become the incident.