Waihi Underground Explosive Principal Hazard Management Plan Approved by: SSE/ General Manager Approval Date:11/05/2021 Next Review: 08/04/2022 OceanaGold Waihi Document ID: WAI-400-PLN-007 Page 17 of 27 6.4.4 Firing Procedure Immediately prior to firing, the face/s and/or stope/s are hooked up in the following order: • Check firing line and bell wire are twitched at both ends • Electric detonator is connected to bell wire • The electric detonator is taped to the green cord • The bell wire is twitched to the firing line Once this process is complete, the shot crew/s retreat to the DFP having ensured the correct signage is hung at the required locations. Clearance to fire is obtained from the Shift Supervisor and the shots may then be fired with an approved initiation device. When firing is complete this must be communicated to the Shift Supervisor. For more information refer to the underground procedure for “Firing from the Portal”. See Appendix I for document details. 6.5 Maintenance / Safety Blasts Maintenance /Safety blasts can be conducted 24/7 365 days a year. A ‘Maintenance / Safety Blast’ is defined as: ‘Blasts for maintenance / safety purposes includes breaking over-sized rocks, trimming / slashing of backs, walls and floors, firing of mis-fired explosives and removal of bridged stopes.’ A maximum of 20Kg of explosives may be used and the blast must not exceed 2 seconds duration and 1mm/s vibration. 6.6 Re-Entry After Firing 6.6.1 Blast Fumes Carbon monoxide (CO) is one of the most hazardous by-product gases of blasting. CO is a colourless, odourless and tasteless gas; it is lighter than air and is extremely toxic even in low concentrations. CO will always be present if smoke is visible therefore gas testing of fume clearance times is required for safe reentry. Nitrous oxide is colourless with a slight smell and nitrogen dioxide is reddish brown and has a distinctive smell. It is heavier than air and is extremely toxic even in low concentrations. Other possible fumes are SO2, CO2 and NH3. 6.6.2 Re-Entry Procedure A minimum of 30 minutes must elapse from the time of firing before entering the fired level to conduct a reentry inspection. No one may enter a blast area until it has been cleared by the re-entry crew or another delegated competent person. To clear a heading the re-entry crew must: • Gain consent from the Shift Supervisor to re-enter fired headings • Use a gas detector to check area is clear of blast fumes. If fumes are still present at unsafe levels the re-entry crew must retreat to fresh air and wait before testing again • Roll up used bell wire and adjust signage to reflect change in heading status • Check for misfires or any other hazards and notify the Shift Supervisor immediately if identified • Notify the Shift Supervisor when level has been cleared and it is safe to resume work For more information refer to the underground procedure for re-entry after firing; see Appendix I for document details. 6.6.2.1 Re-Entry After Maintenance / Safety Blasts Re-entry into an area following a maintenance / safety blast can occur 5 minutes after the firing as long as all other normal re-entry procedures are followed.
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