Summary
A young worker was welding on the transom of an aluminum boat. Flammable vapour underneath the deck was not detected and an explosion occurred. The worker was thrown back about 10 to 15 feet (3 to 4.5 metres). The deck of the boat exploded upwards and hit the ceiling. The worker sustained injuries.

Conclusions

Findings as to causes

• An explosion occurred as the welder was making welding alterations to a small aluminum boat. The welder was thrown to the floor, and parts of the boat hit the shop ceiling.

• The welding arc ignited flammable vapour near the stern. The combination of flammable vapour, air, and an ignition source (the welding arc) created the conditions that caused the explosion.
• Assessment of the potential for flammable vapour ignition and explosion was inadequate. A monitor was not used to test flammable vapour before doing "hot work." There was no passive or mechanical ventilation of the areas containing the boat fuel tank and hoses.
• Supervision was inadequate, allowing work to proceed without the required gas testing. The employer did not provide the foreman or the workers with the required safe work procedures for doing "hot work" near flammable or explosive substances.

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