Supporting Technical Assessments

Waihi Emergency Principal Control Plan Approved by: General Manager/SSE Approval Date: 26/03/2021 Next Review:26/03/2022 OceanaGold Waihi WAI-250-PLN-001 Page 85 of 124 HIGH HCN LEVELS IN LEACH CIRCUIT PURPOSE • To provide guidelines for responding to high HCN gas levels in the leach/adsorption tanks area HAZARDS • Cyanide usually fatal if sufficient quantities HCN gas inhaled RISK ASSESSMENT • Moderate SITE COORDINATOR • Area Manager • Plant Metallurgist • Senior Process Supervisor RESPONSE TO HAZARDS • Do not risk life • Wear full face mask with appropriate filter • Continue regular monitoring for HCN gas • Keep area clear of bystanders – use barricade tape EVACUATION • All non-emergency personnel to be kept clear of the area CONTAINMENT • Notify Supervisor and Mill Manager of high HCN levels • Increase lime addition to leach tank • Shut off cyanide flow • Barricade affected areas • Test HCN levels regularly with full face respirator and filter • Return to normal operation once HCN levels are below 10 ppm. SPECIAL EQUIPMENT • Full face respirator and appropriate filter • Ambulance with additional oxygen equipment on standby EMERGENCY ACTION POINTS • Ensure Site Emergency Co-ordinator is given requested support • Keep an emergency logsheet • Ensure mine management is advised of the emergency at first opportunity and kept up to date EMERGENCY CONTACTS • See general listing in appendix 5 for contact telephone numbers EXTERNAL RESOURCES • Nil

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