Forty Minutes Left in the Tank

Decision: no. Work stops, the tank is cleared, and entry does not resume until the permit conditions are restored and re-verified.

Step by step:

1. Ventilation has been removed. The permit requires continuous ventilation. It is a live control, not a one-off action; without it the atmosphere is no longer the atmosphere that was tested.
2. The readings are stale and single-point. 25 minutes old, taken at mid-point only. Fuel vapour is heavier than air and will pool at the low points; a mid-point reading can be the least representative one. Even 25 minutes of valid conditions does not license the next 40.
3. No standby person. He is leaving for four minutes. Four minutes is longer than it takes to lose consciousness in an oxygen-deficient or vapour-rich space, and it is the period in which nobody would know. A standby person with another task is not a standby person.
4. Rescue is no longer possible. With nobody at the entry point there is no one to initiate retrieval. Non-entry rescue via harness and lifeline requires an attendant present to operate it.
5. The reason to continue is production pressure - an aircraft push-out tomorrow. That is precisely the pressure that confined-space fatalities are built on.

Actions: reconnect and run the ventilation, purge, re-test at several points including the lowest part of the tank, re-authorise with the permit issuer, brief all parties, confirm the attendant and rescue plan, and only then resume. Inform the shift leader and record the stoppage.

Because an alarm threshold is a last-resort trigger, not a target or a safe working level. It is set at the point where you must already be reacting, and it assumes the meter is working, the sample is representative and the reading is current - none of which hold here.

Specific faults with the argument:

• The entry criterion is far tighter than the alarm. For a tank that has contained fuel, the permit should specify a working limit close to zero, with the 10 % figure retained only as an evacuation trigger. Working to the alarm is working to the edge of the margin.
• The reading is old and single-point. Stratification means the bottom of the tank can be several times richer than the mid-point sampled.
• It was taken with ventilation running. Stop the air and the concentration rises as vapour desorbs from sealant and tank walls. The reading described a condition that no longer exists.
• The work itself generates vapour. Disturbing and cutting sealant releases solvent and fuel residues locally, at the entrant's face.
• Other hazards are not measured by LEL at all: oxygen deficiency, toxic exposure to fuel and solvent vapours (aromatics, and isocyanates in some sealants), and heat stress in a small enclosed volume.
• Instrument reliability: the meter must be within calibration and bump-tested before use; a single reading with no functional check proves little.

Correct practice is continuous monitoring by the entrant while inside, with a personal alarm, and an evacuation route that does not depend on someone outside hearing a shout.

Hazards

• Oxygen deficiency - displacement by fuel vapour or inerting residues; no warning symptoms before collapse.
• Toxic exposure - fuel vapour, sealant solvents, curing agents; absorption through skin as well as inhalation.
• Heat stress and dehydration in a small, poorly ventilated volume.
• Restricted egress - awkward access, tools and materials blocking the route, panic in a confined space.
• Static and ignition sources - synthetic clothing, unauthorised electronics, ferrous tools striking.
• Communication loss - the entrant cannot be heard or seen.
• Falls and dropped objects at the entry point.

Controls I would insist on

• Competent, medically fit entrants and a named attendant who does nothing else.
• Air-fed breathing apparatus or an airline respirator with escape set - filter masks are not acceptable in a tank atmosphere.
• Full body harness with lifeline, and a non-entry retrieval plan rigged before entry.
• Low-voltage, bonded, spark-free lighting and tools; anti-static clothing; no personal electronics.
• Written permit with defined test limits, continuous ventilation and continuous monitoring.
• Two-way communication with the entrant, checked before entry.
• Written rescue plan and trained rescuers with BA on site. Nobody enters to rescue without BA and training - multiple-fatality confined-space incidents are typically would-be rescuers.
• Decontamination and first-aid arrangements at the exit, and a briefing that everyone, including the entrant, has the authority to stop the job.