WorkSafe says it doesn't normally end up investigating pranks, after revealing it was a joke that caused a gas explosion and left five workers in hospital last year.
It says a barbecue gas bottle was mistakenly left running overnight in a shipping container at a Wynyard quarter construction site last August.
When the five workers opened the container they could smell gas. One of the workers joked about igniting his lighter and, when he did, the gas exploded.
WorkSafe's Paul Budd says it is unusual for a workplace prank to go so terribly wrong.
Budd spoke to Ingrid Hipkiss.
