entech. WKP Magazine Explosion Simulation – Gas Dispersal Study P a g e | 4 1) Mechanical ventilation by: a) Proposed underground primary fan is linked to the Rise 2 exhaust. i) The simulation’s fixed flow is set to 390 mᶟ/s at full speed. 2) Natural ventilation simulations assume exhaust fan will be closed to surface. a) Damper doors on the primary fan will prevent air reversal when power is turned off. b) Damper doors will not open under natural ventilation pressure. 3) Ambient conditions set to the 95th percentile for mean monthly wet bulb temperatures and their associated coincidental dry bulb temperatures, as defined by ASHRAE, for the Tauranga weather station in NZ. a) Summer conditions: i) WB @ 21 ⁰C. ii) DB @ 23 ⁰C. iii) Surface barometric pressure @ 98.5 kPa. b) Winter conditions: i) WB @ 13 ⁰C. ii) DB @ 15 ⁰C. iii) Surface barometric pressure @ 98.5 kPa. 4) Ventsim™ default presets for ANFO were used to define gas concentrations produced by the explosion of ANFO in bulk storage. It was assumed that these presets would present a conservative outcome regarding risk by toxic airborne contaminants. Those gases provided by Orica Australia, represented in Table 4-2, although the majority are non-toxic to life, were used for calculating gas volume only and were excluded from the rest of the study. a) Individual gas yields, used to determine gas concentrations, are defined under the category of ANFO 92/8 in Ventsim™ and are as follows. i) CO @ 38 L/kg. ii) NO @ 1.5 L/kg. iii) NO2 @ 1.5 L/kg. iv) NH3 @ 1 L/kg. b) Dispersion factor was set to ‘very fast’ to present gas concentrations at their instantaneous highest concentrations. The digital Ventsim™ files ‘Entech_WKP CL_used simulation GT request_03 - Summer’ and ‘Entech_WKP CL_used simulation GT request_03 - Winter’ accompany this report and should be
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