Explosives Inspectorate | Alert | No.103 V 1 | 08 September 2021
A mobile processing unit (MPU) was being used to manufacture blasting explosives, blending ammonium nitrate, fuel oil and emulsion. During this operation, a flame was observed by the operator coming from the incline transfer tube. The most likely cause of the flame was identified as an ignition of diesel vapour emitting from the chute between the incline and delivery augers.
The flame was of short duration and self-extinguished before potentially causing a general fire or explosion. As a precaution, the MPU operator used onboard extinguishers to mitigate the risk of fire.
The authority holder’s investigation of the incident found the most likely cause of the ignition was from a hot spot created from metal-to-metal contact in the delivery auger.
It was identified that the incline auger chute had contacted a discharge auger flite. The resulting friction created a hot surface with the level of heat produced by the friction in the order of >300°C. The presence of a fuel oil (diesel), air mixture in the immediate area of the hot spot led to an ignition event.
The investigation identified that the lack of auger engineering design tolerances was a contributing factor combined with inadequate critical control maintenance of the augers. This resulted in metal-to-metal contact between the first flight of the discharge auger and the lower end of the incline auger transfer chute.
To prevent a recurrence of this type of significant incident the following recommendations are made:
Investigations are ongoing and further information may be published as it becomes available. The information in this publication is what is known at the time of writing.
We issue Safety Notices to draw attention to the occurrence of a serious incident, raise awareness of risks, and prompt assessment of your existing controls.
Contact: Haydn Isaac, Principal Inspector of Explosives explosives@rshq.qld.gov.au
Issued by Resources Safety & Health Queensland
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All information on this page (Ignition of fuel-air mixture from mobile processing unit discharge auger - https://www.rshq.qld.gov.au/safety-notices/explosives/ignition-of-fuel-air-mixture-from-mobile-processing-unit-discharge-auger) is correct as of time of printing (Apr 26, 2024 11:09 am).