50 Tonkin & Taylor Ltd Hazardous Substances Technical Assessment – Waihi North Project - Waihi Processing Plant, Water Treatment Plant and Development Site Oceana Gold (New Zealand) Limited June 2022 Job No: 1015212.1000 vRev0 7.3.2 Partial quantitative analysis of Class 1 explosion Partial quantitative analysis has been undertaken for the consequence of a detonation at the explosives store by considering the level of damage expected at specific overpressure values provided by HIPAP-4. The maximum overpressure levels off-site anticipated in the event of a detonation at the new Class 1 explosives store has been provided by GSS’ calculation of the overpressure radii around the store in accordance with AS 2187.1 1998 – Explosives, Storage, Transport and Use – Storage, as shown inFigure 6.1. The calculated radii show that an overpressure level of 2 – 5 kPa could be experienced by a person near the OGNZL boundary on the farmland to the northeast. The predicted overpressure levels at off-site locations are considered in terms of the expected effect provided in Table 7 Appendix 1 of the Hazardous Industry Planning Advisory Paper No.4 (HIPAP-4), Risk Criteria for Land Use Safety Planning, published by the State of New South Wales through the Department of Planning in 2011 This table is copied as Figure 7.2 below. Figure 7.2: Effects of explosion overpressure Source: HIPAP-4 Overpressure levels below 3.5 kPa are not discussed, and are presumed to be negligible. At 3.5 kPa, most glass is expected to crack or break, but the potential for injury to individuals is described as very low. At 7 kPa, repairable damage to partitions in buildings is anticipated along with a 10% probability of injury. There are no off-site areas exposed to 7 kPa. The injury probability for the maximum off site over pressure level of 5 kPa is therefore lower than 10% and, were a building to be located within the 2 – 5 kPa area, there may be some repairable damage to buildings in the form of cracked glass or damaged partitions. A person in the 2 kPa – 5 kPa radius, such as a farmer on the rural property to the northeast, would be expected to hear a brief audible noise in the range of 160 – 170 dB from the blast overpressure. At this level, the sound would be likely to cause the person short term pain and ringing in the ears, similar to the effects of standing close range to a firework or shotgun fire. With consideration of the level of impact at the maximum overpressure level, the consequence of a detonation in the Class 1 explosives store to human health and property is minor.
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