14 Tonkin & Taylor Ltd Wharekirauponga Underground Mine – unplanned detonation air quality assessment Oceana Gold (New Zealand) Limited June 2022 Job No: 1015212.2000 vRev0 Table 5.5: Relative gas yields by explosive type for scaling the model predictions Contaminant Gas yield (m3 gas per 1000 kg NEQ) Booster to ANFO yield ratio for scaling the model predictions ANFO Booster N2 263.2 114.8 44% NOX 3.0 0.81 25% N2 and NOX 266.2 115.5 43% CO 38 67.6 178% NH3 1 58.7 5,866% 1. Assuming equal yield of NO to NO2 as provided for ANFO. The comparison of the gas yields for the two explosive types shows that in the event of a detonation of booster explosives, almost twice as much CO and up to 59 times as much NH3 may be produced as for a detonation of ANFO. However, lower volumes of both nitrogen gas and oxides of nitrogen are anticipated in a booster detonation scenario. The scaling factor of 43% has conservatively been applied to the NOX predicted GLCs. Using these scaling factors, the estimated GLCs for the contaminants of interest are provided in Table 5.6 below. Table 5.6: Evaluation of scaled GLCs for a booster detonation against assessment criteria Contaminant Assessment criteria (µg/m3) Pro-rated GLC (µg/m3) Predicted location Background concentratio n (µg/m3) Cumulative GLC (µg/m3) IAQM impact descriptor CO 30,000 816 (2.7% of criterion) 130 m NE of vent 5,000 (16.7% of criterion) 5,816 (19.4% of criterion) Negligible NOX (as NO2) 200 25.8 (13% of criterion) 130 m NE of vent 37 (19% of criterion) 62.8 (31% of criterion) Moderate NH3 21,000 1,143 (5.4% of criterion) 130 m NE of vent 0 (0% of criterion) 1,143 (5.4% of criterion) Slight The results are discussed in terms of the effect on human health in Section 6. 5.6 Conservatism in results The model results as provided in in the previous sub-sections are considered by T+T to be conservative due to the following: The contaminant concentration assumes that 100% of the full capacity of the magazine chamber combusts instantaneously. The emission rates used in the modelling assume that the contaminants are emitted from the surface connection at the continuous discharge rate for a full hour. In reality, the contaminant emission rates have been determined through Entech’s Gas Dispersal Study inAppendix A to be exhausted from the mine in 15 minutes and 40 seconds. This will conservatively result in the modelling representing up to 4 times the mass of contaminants that will be produced by the detonation of one chamber.
RkJQdWJsaXNoZXIy MjE2NDg3