entech. WKP Magazine Explosion Simulation – Gas Dispersal Study P a g e | 1 1 SUMMARY Analysis of contaminant dispersal following the simulated unintentional detonation of explosive storage, underground at Wharekirauponga (WKP) mine in NZ, was completed using Ventsim™ software. Worst case was measured using simulation presets for ANFO explosives, with the maximum bulk storage exploding as a single event and no resulting fire. The maximum bulk storage of ANFO was 1 t, and the simulation was set to the fastest dispersal factor so that maximum concentration of explosion gases could be simulated. Only gas concentrations exiting to surface were reported. An underground assessment of gas dispersal around workplaces is out of scope for this report. Tonkin and Taylor (T&T) will carry out the environmental impact for the surrounding nature reserve. They requested the following information to complete their work: • Only those gases produced from ANFO that are toxic to life were analysed. o Carbon monoxide (CO). o Nitrous Oxide (NO). o Nitrogen Dioxide (NO2). o Ammonia (NH3). • Total volume of gas produced by the explosion. o Calculated at 1,007 mᶟ (see section 4.2). • Discharge rate in grams per second (g/s) for contaminants exiting to surface. o Converted from gas concentrations (see Table 4-3). • Discharge duration to be a minimum of one hour. o Full discharge duration of contaminants is provided in section 4.4. • Air volume, velocity, and temperature of discharge at surface (see section 4). o There was no change in air speed or temperature at surface connections. o Shortest air path from the explosion is 650 m if exhausting via Rise 2. • All the gas will be ejected to the nature reserve above under mechanical ventilation (primary exhaust fan operating) via Rise 2. • Surface connection dimensions, along with their coordinates are mentioned in Section 4. Seasonal variance was assessed for natural ventilation flow in the event of power failure. Overall mine airflow drops to 4% of the total flow under mechanical ventilation and gas can take more than three days to clear the mine. Subsequently, gas concentrations peak 80% less than when fans are running at full speed.
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