44 Tonkin & Taylor Ltd Hazardous Substances Technical Assessment – Waihi North Project - Storage and use of hazardous substances at Willows Road site and the Wharekirauponga Underground Mine Oceana Gold (New Zealand) Limited June 2022 Job No: 1015212.1000 vRev0 Overall, given the level of conservatism inherent to modelling of the detonation scenario, the impact to human health from discharge of contaminants from the surface vent is very low. 7.3.2.3 Consideration of known industry events A detonation in an explosives store managed in accordance with the HSW-HS is considered unlikely. Detonations in Class 1 explosives stores are not common in the mining industry. OGNZL staff note only one known occurrence locally, which was a detonation underground in the Telfer Mine in Western Australia in 2005. The Mines Safety Bulletin detailing the causes and consequence of this detonation is attached as Appendix J and summarised as follows The detonation occurred in a store that was not designed for high volumes of explosives. It occurred in a “working party magazine”, a term for a small temporary store of explosives and detonators (typically <200 kg NEQ) for use by a group working in a particular area in an underground mine. In this case the temporary store was established with more than 6,000 kg NEQ of high explosives and up to 3,000 detonators all in the one chamber. Additionally, the store contained waste packaging debris from the spent explosives, and had been the site of a spill of ANFO in an environment with reactive sulphide-containing minerals. When a fire started in the store, it burned for two hours before the detonation occurred. Efforts to put out the fire were hampered by the lack of a water deluge system and fire hoses for fire fighting, the unsuitable class of fire extinguisher available, and inappropriate forced ventilation. The consequence of this 6,000 kg class 1 explosive detonation to human life was limited due to timely worker evacuation, however it did cause significant damage to mine underground services, ventilation doors and machinery. The contributing factors in this event would not lead to a detonation in OGNZL’s proposed operation. All stores are designed to meet the standard AS 2187.1. for Explosives Storage Transport and Use, including quantity limits (1,750 kg NEQ in the largest magazine), provision of deluge fire suppression systems, and systems for waste management. OGNZL has not had any such incidents in any of its existing explosive stores and has a number of additional controls to prevent such an incident. A likelihood rating of “unlikely” is considered appropriate for the event. Additionally, the long delay (two hours) between ignition of the fire in the Telfer mine working magazine and the detonation of the explosives illustrates how explosives in storage are less volatile than explosives that have been properly prepared and densely packed into a blast hole for mining. This example illustrates that instantaneous and complete detonation of the contents of a magazine is an unlikely scenario. 7.3.3 Risk analysis A qualitative risk assessment of the identified hazards/failure modes has been undertaken for all of the scenarios identified in the hazard analysis inTable 7.1 where there is the potential for offsite effects. The qualitative risk assessment has been carried out inAppendix Kin accordance with the method described in ME339, by applying a qualitative rating to the frequency (likelihood) of the failure occurring and the consequence (severity) of impacts if the event were to occur. The likelihood and consequence ratings take into account the controls (mitigation and management measures) that will be in place.
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