entech. WKP Magazine Explosion Simulation – Gas Dispersal Study P a g e | 3 2 SIMULATION PARAMETERS & ASSUMPTIONS 2.1 DESIGN PARAMETERS & ASSUMPTIONS For contaminant dispersal, following unintentional detonation of ANFO in underground bulk storage facility, the following parameters and assumptions were used. Table 2-1 – Parameters and definitions used in this study. Parameter Description Design Parameter Remarks Hazard is defined by workplace exposure standards for airborne contaminants. Toxic gases associated with ANFO explosives; carbon monoxide (CO), nitrous oxide (NO), nitrogen dioxide (NO2) & ammonia (NH3). Gas TWA (ppm) STEL (ppm) Exposure standards set by Work Safe NZ. *The short-term exposure limit (STEL) for CO was derived from the 60 min short term excursion limit per 8-hour shift (different to that which defines STEL). **Where a limit was not made available, Safe Work Australia’s was used. CO 25 50* NO 25 45** NO2 1 5** NH3 25 35 Maximum storage capacity for ANFO underground. 1,000 kg Maximum individual storage limit. Resulting explosions from additional storage capacities were not considered in this study. Surface Connection. Airway opening to underground mine workings. Boundary between underground and surface atmosphere. Mechanical ventilation. Airflow according to fan pressures. Underground airflow defined by the mechanical action of an industrial fan. Natural ventilation. Airflow in the absence of primary fans. Underground airflow defined by ambient conditions, with air entering and exiting the mine according to natural pressure changes. Analysis and outputs for this study were generated using Ventsim™ simulation software. A calibrated working model of the mine ventilation network was provided by WKP along with the following design assumptions.
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