Collapse at the bottom of a cargo tank: the second casualty problem
You are the designated first aider on a 12,000 dwt product tanker alongside a terminal. The No. 3 port cargo tank has been discharged, washed and ventilated, and an entry permit was issued this morning after a reading of 20.8% oxygen taken at the top hatch. At 1445 a pumpman goes down the tank to recover a dropped torch without telling the officer on deck. Two minutes later a fitter looking down the 9-metre tank sees him lying motionless on the tank bottom and shouts for help. You arrive to find the fitter tying a rope around his waist, preparing to climb down. A breathing apparatus set, harness and lifeline are in the pump room, and the vessel's rescue team is being mustered but will not be ready for at least eight minutes. No reading of the atmosphere at the tank bottom has been taken. The pumpman is wearing coveralls only, with no harness.
1. The fitter is about to climb down with a rope. What do you say to him and what is your reasoning?
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Stop him, physically if necessary, and take the rope. A rope with no breathing apparatus is not a rescue; it is the fastest way to create a second casualty and then a third when someone else goes after him.
Unexplained collapse in a tank must be treated as an atmosphere problem until proved otherwise. The 20.8% reading was taken at the top hatch and is now old; oxygen consumption by residues, displacement by heavier vapours and pockets of hydrogen sulphide or solvent vapour near the bottom can leave a lethal atmosphere a few metres below a breathable one. At very low oxygen, consciousness is lost within a breath or two, so the fitter would be unconscious before he could shout.
While the rescue team musters: raise the alarm to the master, stop all work on the tank, post a man at the hatch to keep watch and talk to the casualty, start or maintain mechanical ventilation, and have oxygen, a bag-valve-mask and suction ready at the hatch. Do not lower equipment that could tangle or strike him. Nothing enters that tank until the conditions at the bottom are known and the entrant is protected.
2. What conditions must be in place before any rescuer enters the tank?
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All of the following, authorised by the master or a responsible officer, not by whoever is closest to the hatch:
- Atmosphere tested at the bottom of the tank with a calibrated meter for oxygen, flammable gas, hydrogen sulphide and carbon monoxide, with continued ventilation and re-testing.
- Entrant wearing self-contained breathing apparatus with sufficient duration and a proper face fit, plus a harness and a lifeline tended by a standby man outside.
- A trained rescue team, not a single volunteer, with a designated leader.
- Reliable communication between entrant, standby man and the officer in charge.
- Resuscitation equipment, oxygen and a stretcher at the hatch, with a route to the ship's hospital cleared.
- A new entry permit reflecting the emergency, entry and exit logged, and no lone entry at any point.
Explain to the crew why speed here means preparation, not haste. The eight minutes spent dressing a properly equipped rescuer is shorter than the time needed to recover two bodies.
3. The pumpman is brought up unconscious but breathing weakly. Describe your first aid and what you record.
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Land him on deck, not in the tank, and check response, airway and breathing. If he is breathing but unresponsive and there is no evidence of a fall injury, put him in the recovery position so vomit drains, and keep the airway open. Give 100% oxygen by non-rebreather mask at 15 L/min. If he is not breathing normally, start CPR at 30:2 with the bag-valve-mask and high-flow oxygen, attach the AED as soon as it is available and follow its prompts. In oxygen-deficiency collapse, ventilation is as important as compressions.
Remove wet or contaminated clothing, keep him warm, and look for head or spinal injury from the fall at the bottom of the tank or from the lift out. Check his blood glucose if a meter is available, since hypoglycaemia mimics this picture. Suction should be ready because vomiting is likely.
Record: time of collapse, time found, time removed, estimated time in the atmosphere, oxygen saturation if measurable, pulse, respiratory rate, level of consciousness at each check, interventions and oxygen flow. Even if he wakes up, he must be medically assessed and evacuated: hypoxia can cause delayed cerebral and pulmonary effects, and the atmosphere exposure may have been to a toxin as well as to low oxygen.