Description of the accident

The timing cover of auxiliary booster exploded and shattered during normal reverse circulation drilling operations. Debris from the timing cover was projected distances of over 15m into an area where personnel could have been working. Fortunately, no personnel were in the line of fire at the time of the event and no injuries were reported.

Apparent Causes

A booster is essentially an internal combustion engine but instead of a combustible fuel mixture being injected into the cylinders, high-pressure compressed air is injected and the reciprocating action of the pistons then further compresses the air in the cylinders.

In this case, one of the pistons melted and so extremely high pressure compressed air was allowed to by-pass the piston and enter the timing belt compartment where it caused the timing belt cover to explode and spray fragments of metal across the drill site.

Investigation of the accident revealed the following:

1.     The recommended service interval for the booster was 250 hours but this booster had not been serviced for over 2 000 hours at the time of the accident!

2.     The temperature sensor on the booster was not operational and so the automatic shutdown of the unit was not operating. This was either not identified during pre-start inspections, or if it was identified, the hazard was ignored.

Recommendations

The drill rig used on this operation was a state of the art drill with a number of safety and productivity innovations installed. These innovations were all installed to control perceived risk yet the most fundamental control, proper and complete pre-start inspections was ignored. 

It seems incomprehensible that a piece of equipment like a booster could have been neglected for such a long period of time. 2000 operating hours is possibly 12 to 18 months of operation and this suggests that a less than adequate safety management system was in place.

While the introduction of new innovative equipment is to be applauded, we must never forget how important it is to ensure that all basic controls are fully and correctly implemented.