In two recent incidents in Tasmanian mines, shot firers and their assistants were injured by air blasts. Both incidents caused significant damage to the shot firers? vehicles and to mine infrastructure and could have resulted in serious injuries or fatalities. The shot firers were also exposed to large quantities of firing fumes and dust following initiation of the shots.
CONTRIBUTING FACTORS
In both incidents, the cause of the air blast was the unconfined detonation of a large quantity of ammonium nitrate fuel oil (ANFO) that had fallen out of the upholes.
Investigations found that:
? The shot firers did not consider the possibility of an air blast when selecting the firing locations.
? Problems were experienced with the pressure reducing valves on the charge up units, resulting in ANFO failing to pack sufficiently in the upholes.
? In one incident, spiders were not used to hold the primers in position.
? Spilled ANFO may not have been adequately dissolved before firing the shots.
RECOMMENDATIONS
WorkCover Tasmania and Workplace Standards Tasmania recommend that shot firers should:
? Consider the possibility of air blast when selecting firing locations. If possible, fire all shots from a location remote from the blast.
? Ensure that there is adequate compressed air pressure at the charging hose to pack the ANFO in upholes. This may require additional maintenance or checking of the pressure regulators.
? Ensure that when ANFO is spilt during charging, it is dissolved with water before the shot is initiated.
? Ensure that devices such as spiders are used to secure the primers in upholes.
? Communicate the dangers of air blast to charge crews and supervisors.
This article is reprinted from Workplace Issues (No 54, June 2009), a free publication of WorkCover Tasmania. For further information, visit www.workcover.tas.gov.au