6 Tonkin & Taylor Ltd Wharekirauponga Underground Mine – unplanned detonation air quality assessment Oceana Gold New Zealand Limited June 2022 Job No: 1015212.2000 vRev0 Oxides of nitrogen (NOX), primarily comprised of nitrogen oxide (NO) and nitrogen dioxide (NO2). NO2 is visible as a brown gas and is a respiratory irritant. Ammonia (NH3), a flammable and corrosive gas. 3.2.1 Emission scenarios In the event of an unintended detonation, the overpressure would propagate through the mine space and be expelled at the surface connections identified in Section 2.1. These locations are the key sites at which there is potential for effects on off-site people or property in the event of an unintended detonation at the storage facility. The gas dispersal report prepared by Entech attached as Appendix A describes three emission scenarios, summarised as follows: 1 No damage to mine ventilation systems, mechanical ventilation of explosion gases resulting in emissions from Rise #2 (Site 5) 2 Failure of the mine ventilation systems due to damage from the explosion. Two natural ventilation scenarios are possible due to the different seasonal conditions resulting in emissions either to Rise #1 (Site 4) or the access portals at Willows Road and Waihi (Sites 1 and 2). In the natural ventilated scenarios, the following is airflow restrictions will apply: a Damper doors on primary fans prevent the reversal of airflow when fans are switched off. b Damper doors will not open under natural ventilation pressure. Ventsim modelling was carried out for the scenarios listed above by Entech. From this, the scenario in which the mine’s mechanical ventilation continues to function provides the greatest volumetric flowrate and the highest concentration of contaminants and releases the contaminants over the shortest timeframe. Consequently, Scenario 1 is considered the most conservative for the purposes of this assessment. The emission profile for the mechanically ventilated scenario (Scenario 1) was predicated on the following conservative assumptions that were made by Entech: there is a sufficient ignition source within one of the chambers to create an explosion. the chamber contains its maximum licenced capacity of explosives (1,000 kg NEQ). 100% of the product will combust instantaneously (this is considered unlikely due to the low packing density of the storage chamber compared with a blasthole). Entech advises that this scenario will produce a higher concentration of gaseous contaminants at the vent stack than would be anticipated in reality. A summary of the parameters that apply to each scenario is provided in Table 3.1.
RkJQdWJsaXNoZXIy MjE2NDg3