Hot work over a heated fuel tank beside an open paint-locker vent

Deficiencies and ranking:

1. The tank is heated to 62 C, above the 60 C flashpoint of its contents. Once a liquid is above its flashpoint, its ullage space can hold a flammable mixture at ordinary ambient temperature, and the deck plate the welder is standing on is the top of that tank. Welding heat conducts into the plate and raises the vapour space further.
2. Hot work 3 m from an open vent head of a paint locker holding thinner with a 21 C flashpoint. That liquid gives off flammable vapour at normal daytime temperatures, and the vapour is heavier than air, so it creeps along the deck.
3. Permit issued by an officer with no training or delegated authority. A permit must be authorised by the master or chief officer after a joint inspection of the site.
4. No fire watch, no screens or blankets, no extinguisher at the site, no charged hose run out.
5. The gas test was taken at deck level in the open air, 15 minutes before work, not at the leak paths, not in the space below, and not repeated.

Ranking: the flammable vapour from the paint locker and tank ullage is an explosion risk to the whole deck and comes first; loss of ignition control and the absent fire watch come second; the missing extinguisher third.

LEL is the lowest concentration of vapour in air that will support a flame, and meters express a concentration as a percentage of that limit. A reading of 6 percent LEL means the atmosphere is at 6 percent of the flammable threshold, roughly 16 times below the point at which it will burn. That is not a safe reading, it is an early warning:

• The vapour source is live and reaching the sample point. The trend matters more than the number: another reading a few minutes later at 12 percent is heading for an emergency.
• The meter responds to its calibration gas; different vapours give different responses, so a reading can under- or over-state the true concentration.
• Thinner vapour is heavier than air and pools at low level, so sampling only at deck level may miss the worst of it.

Action: stop the hot work immediately, do not touch the welder or any electrical switch in the vapour, move non-essential crew upwind and clear of the area, close the paint-locker vent head and restart the extract fan or keep the locker sealed, ventilate the deck, then re-test at several levels with a calibrated instrument. Work resumes only under a correctly authorised permit, and the master is informed.

Permit conditions:

• Authority: issued by the master or chief officer after a joint site inspection with the contractor; time-limited, location-specific, posted at the site, and withdrawn if conditions change.
• Preparation: combustibles removed or screened within 10 m; deck openings, vents and soundings sealed; the paint locker sealed with its fan running; drains plugged so sparks cannot fall; the tank below either certified gas-free or the job relocated to a plate that is not the top of a tank holding oil above its flashpoint.
• Testing: oxygen near 20.9 percent, 0 percent LEL, and no flammable gas in adjacent or lower spaces; readings recorded at the time and place of work with the instrument's calibration current.
• Equipment: extinguisher and charged hose at the site, fire blanket, screens, welding plant earthed and checked.
• People: a trained fire watch who does nothing else, positioned where sparks actually fall, including the other side of a bulkhead, with a means of raising the alarm.

Fire watch duties: continuous observation of the work and the area below and behind it; keep the extinguisher and hose ready; stop the job on any smell of gas, change of conditions, or spark carry; know the alarm and muster signals.

After work: continue the watch for at least one hour after the last hot spot, check the space below and behind the bulkhead with a thermal imager, then close the permit with a signature.