18 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 Table 4.2: Offset distances Scenario Minimum offset required1 Provided separation Blast propagation by rock spall 5 m 10 m Blast Propagation by Flames and Hot Gases 10 m Major Damage Prevention to Interior of Facility 10 m 1 Calculated in accordance with Annex M of IATG 2.20 The separation distance between the chambers containing 1,000 kg of Class 1 explosive meet the calculated minimum at which blast propagation between chambers is unlikely. The minimum offsets have been calculated on the basis that the NEQ stored has a one-to-one equivalence to trinitrotoluene (TNT) in terms of energy released, when in reality many of the explosives at the facility have a lower TNT equivalence. This assumption results in higher separation requirements with a degree of conservatism. 4.2.3 Hazardous substance location for ANE 4.2.3.1 Surface storage area The ANE and gasser will be stored in 1,000 L IBCs within a dedicated compound for the oxidising substances at the SFA on the Willows Rd site. This compound will be secured from access by unauthorised personnel. ANE and gasser are incompatible and will be stored in designated sheds at a minimum distance of 8 m apart. There will be no combustible materials stored or used within 8 m of the ANE storage shed. The closest residence that is not owned by OGNZL is approximately 400 m from this storage area. Both substances will be stored in storage sheds that protect them from direct sunlight and ensure temperatures will remain under 50 degrees and below maximum temperatures associated with decomposition of the substances. Each shed will have secondary containment for at least 50% of the total storage capacity for ANE and 25% the total storage capacity for the gasser at minimum. Any damaged or leaking container will be captured in the provided secondary containment. The storage area is located in the SFA which drains to treatment as described in Section 4.9 to manage any residual contamination. The location will be certified to meet the relevant controls specified in the HSW-HS regulations as set out inTable 4.1. The compound will also be designed to provide designated areas for storage of the empty IBCs such that they are not stored together at any time, given the potential for residual material being present in both. 4.2.3.2 Underground storage area ANE and gasser will be stored underground in the WUG in three separate chambers – two for ANE and one for gasser (separated from the others by a minimum of 10 m). These chambers have been designed with consideration of legislative, safety and operational objectives, and are suitably separated as required for incompatible substances, as indicated inFigure 4.3.
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