13 | P a g e Class 1 Storage Location Assessment_Oceana Gold NZ Ltd Wharekirauponga Underground Mine 5.3 Blast from Tunnel Entrance – Controlled Zone Effects. The ‘blast distance from tunnel entrance’ formula outlined below have been utilised to estimate the radius of the surface controlled zones. The total volume (tunnel volume) in consideration of the nearest surface connection (WUG RAR #2) from the magazine facility has been established at ~90,229 m3. All controlled zone calculations at surface connections have been based upon the assumption of a singular detonation event in one magazine chamber only. The largest stored quantity (NEQ) of 1,000 kg (H.E.) has been used. All tunnel and magazine chamber volume calculations have been undertaken and provided by Oceana Gold and are based upon the currently proposed mine designs. Varying types of commercial explosives (H.E or I.E) will be stored in each of the seven magazine chambers. All controlled zone calculations are based upon ‘ TNT equivalence’ (See definitions). ‘ANNEX M’ of IATG 2.20’ describes specific ‘Quantity Distance’ (QD) factors in relation to known criteria and allowable surface overpressure outputs. Some of the criteria align with New Zealand Regulations. For example, Inhabited Building Distance (IBD’) would be equivalent to 5 kPa within Health and Safety at Work (Hazardous Substances) Regulations 2017’, r 9.27 (2)(c) ). However, other criteria within the New Zealand Regulations such as ‘public traffic routes of medium density – 9 kPa (r 9.27 (2)(b)) have no comparable QD factors available. In the absence of appropriate QD factors, such criteria have been scaled against known QD factors within Annex M to align with remaining controlled zones detailed in ‘Health and Safety at Work (Hazardous Substances) Regulations 2017’, r 9.27 . ‘Health and Safety at Work (Hazardous Substances) Regulations 2017’, r 9.27, considers several controlled zone threshold requirements. A summary of these is included in the following paragraphs along with a description of how each surface connection complies with the legislative requirements. Controlled zone definition – 24 kPa r 9.27(4)(a) – A PCBU with management or control of a hazardous substance location that is used solely for securing and holding a class 1 substance must limit the quantities of any class 1 substance at the location to ensure that, in the event of an unintended initiation, - i. the interior of any proximate building where a class 1 substance is manufactured would not be subject to a blast overpressure of more than 24 kPa. Formula for minimum offset distance in accordance with the above criteria - D = 16 x HD x LD 1/3 Proposed class 1 site - Compliance summary for 24 kPa controlled zone. • This is currently not applicable as the manufacture of class 1 substances at the site is not being considered at present. • Should manufacture be considered, this would likely occur at a surface facility only. In the instance where Ammonium Nitrate (A.N) was to be used, ‘ Table 3.2.3.2’ , Associated Works’ of ‘ AS 2187.1’ would then apply in relation to minimum offsets to ‘A.N storage. • Controlled zone offsets shall be considered if class 1 manufacture does occur.
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