Wet Wing Entry with a Grinder Running Next Door
It is 2130 in a Metro Manila hangar. A King Air 200 is in for a fuel leak at the inboard access panel of the right wet wing. You are the only licensed AMT on shift, with one helper. The affected bay is defueled to roughly 40 litres. The hangar's portable blower is a standard shop fan with a brushed electric motor. In the next bay a contractor is cutting the frame of a hangar door with an angle grinder, throwing sparks. The helper has already climbed into the tank with a 230 V trouble light, no attendant is posted, and the aircraft battery is still connected because the fuel quantity indicating system is being checked. The safety data sheet for Jet A-1 says to avoid inhalation and skin contact. You have a half-face respirator with organic vapour cartridges, but your fit test expired eight months ago.
1. List the hazards of this tank entry and the controls that must be in place before anyone goes back in.
Read the worked answer
The tank is a confined space with a flammable atmosphere, and almost every control is currently missing.
Hazards: fuel vapour above the lower explosive limit; displacement of oxygen; skin contact and dermatitis; ignition from the brushed fan motor, the 230 V lamp, or the battery still connected to the fuel quantity harness; lone entry with no rescue capability.
Controls before entry:
- Defuel and purge the bay per the AMM; keep bonding and grounding leads on.
- Continuous mechanical ventilation using an air-driven or explosion-proof blower - the shop fan is an ignition source and must come out.
- Low-voltage (12/24 V) explosion-proof lighting; the 230 V trouble light must come out.
- Disconnect and lock out the battery; tag the fuel quantity circuit.
- Atmosphere test at entry and continuously: oxygen 19.5–23.5%, flammable vapour below 10% LEL.
- A posted attendant with communications, a rescue plan and rescue equipment.
- An entry permit signed by a competent person, and PPE including impermeable gloves and eye protection.
2. The contractor starts grinding again while your helper is in the tank. What is the immediate action and what has to be agreed before either job continues?
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Immediate action: get the helper out of the tank and stop the grinding. Do not attempt to 'work around' it - vapour and sparks do not respect a bay boundary.
The two jobs are incompatible while run concurrently in the same hangar volume. Before either restarts:
- A hot work permit must be raised for the grinding, with a fire watch, suitable fire extinguishers, and screening to contain sparks.
- The hot work must be physically separated from the fuel work - the usual standard is at least 35 ft, with a fire blanket or screen - or the jobs must be sequenced so only one happens at a time.
- The contractor's supervisor and your accountable manager must agree the sequence in writing, and the hangar's ventilation must be running.
You have the authority and the duty to stop unsafe work. Stopping production for one shift costs far less than a tank explosion, and the contractor's schedule is not your responsibility.
3. Your respirator fit test is eight months old and no attendant is available. What does that mean for the entry, and who can authorise a change?
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It means you do not enter.
A respirator is only protective inside a functioning programme: current fit test, current medical clearance, and a cartridge appropriate to the contaminant. An organic vapour cartridge is also the wrong tool for an oxygen-deficient or immediately dangerous atmosphere - that calls for supplied air or a full assessment, not a half-face mask. An expired fit test means the seal is unverified, and a leaking seal on fuel vapour is worse than no mask because it creates false confidence.
No attendant means no entry, full stop. The attendant is the rescue system: someone who stays outside, maintains communication, and calls for help without becoming a second casualty.
Authority: the entry permit is signed by a competent person designated by the AMO, and only that person - with the accountable manager - can authorise entry conditions. Neither the schedule nor the client can authorise it, and your refusal should be recorded in the shift log.