Queensland Mining Industry Health & Safety Innovation Awards 2007

Transcription

1 Queensland Mining Industry Health & Safety Innovation Awards 2007 Reduction of the Workplace Airborne Contaminant Mercury through the Implementation of a Retractable Furnace Shield Newmont Pajingo Operations Innovations Submission June 2007 Prepared by David Champion Page 1 of 9 15/06/07

2 1. EXECUTIVE SUMMARY This report details the innovation of a retractable furnace shield implemented at the Newmont Pajingo Operation s (NPO) to assist in the prevention and control of occupational risk of the workplace airborne contaminant Mercury in the site s gold room and processing circuit areas. The key areas detailed in the report include; The Problem. The Solution. Benefits/Effects. Transferability across Industry Innovation As a result of the innovation implemented at NPO the level of risk to the gold room workers from the workplace airborne contaminant Mercury has been significantly reduced. Prepared by David Champion Page 2 of 9 29/09/2006

3 TABLE OF CONTENTS 1. EXECUTIVE SUMMARY INTRODUCTION THE PROBLEM THE SOLUTION BENEFITS / EFFECTS TRANSFERABILITY ACROSS INDUSTRY INNOVATION CONCLUSION REFERENCES...3 Prepared by David Champion Page 3 of 9 29/09/2006

4 2. INTRODUCTION This report details the innovation of a retractable furnace shield implemented at the Newmont Pajingo Operation s (NPO) to assist in the prevention and control of occupational risk due to the workplace airborne contaminant Mercury in the site s gold room area. 3. THE PROBLEM The run-of-mine ore is crushed and ground to an optimum particle size to make the ore amenable to gold extraction. The next step in the process is to leach the precious metals from the gold-bearing ore with a weak cyanide solution. In this step, the precious metals and mercury are solubilised into the cyanide solution as cyanide-metal complexes. Final processing in the gold room results in the Mercury being heated and vaporised into the surrounding environment (MSHA, 1997). It is important to note that inhalation represents the most significant route of uptake for mercury into the body with approximately 80% of inhaled mercury being absorbed through the lungs. Health effects of Mercury exposure can range from severe levels of acute exposure resulting in shortness of breath, malaise, nausea, vomiting, and diarrhoea and even death to more long term effects such as a variety of symptoms, including blurred vision, dysarthria, prominent gingivitis, tremor, unsteady gait, and slow mental response (World Health Organization, 2003). 3.1 Hazard Identification Process Mercury was first identified as a potential hazard at NPO several years ago through a full spectrum analysis of the metals contained in the site s ore body, the levels of Mercury identified were however quite low and did not pose a health risk to NPO workers. A more recent analysis of the loaded carbon from within the operation s gold processing circuit identified much higher levels than ever seen in pervious ore samples. A contract hygienist (Simtars) was brought in to take a variety of samples using various sampling methods, including direct vapour measurements using a Jerome Vapour Analyser (Figure 2), static and personal exposure levels using Inorganic Mercury Passive Sampler badges (Figure 3) and bench top swab samples in an effect to determine the exposure values present at NPO. Several ventilation tests were also conducted using smoke tubes and a wind anemometer. Prepared by David Champion Page 4 of 9 29/09/2006

5 Figure 2 - Jerome Vapour Analyser Figure 3 - Sampler Badge 3.2 Risk Assessment Methodology Quantitative risk analysis was conducted using concentration readings of the airborne contaminant Mercury gained from the Jerome meter in contrast to the Time Weight Average (TWA) exposure for an 8 hour shift. The results highlighted that readings of up to mg/m3, almost ten times the threshold limit value (TLV) for Mercury of mg/m3 set by the NOHSC were recorded, therefore posing an extreme risk to the health of the workers, requiring significant engineering controls to be investigated and implemented. The NOHSC guideline was also compared to global best practices to ensure adequacy of the standard, in particular the guidelines available from the American Conference of Governmental Industrial Hygienists (ACGIH) and the Health and Safety Execute (HSE) in the United Kingdom. 4. THE SOLUTION The hierarchy of control was utilised as the underlying principle for examining current and future controls for reducing the level of risk to the operators from exposure to Mercury. Following is a summary of the recommendations from this review. Method Current and Future Controls Possible Failings & Resolutions 1. Elimination It is not possible to eliminate the Mercury from the ore as it is naturally occurring in the gold bearing ore. It may be possible to remove the mercury from the processing circuit prior to the smelting process. Sodium hydrosulphide (NaHS) for example may be added to the leach slurry to precipitate mercury as a sulphide. The mercury then leaves the circuit with the tailings, and does not load onto the gold bearing carbon. This option has not yet been explored at NPO, however it has been noted that not all of the mercury bearing minerals are cyanide soluble. One US plant reported considerable success following addition of NaHS. The amount of mercury recovered reduced by up to 10 kg per electrowinning cycle. (MOSHAB, 2001) Prepared by David Champion Page 5 of 9 29/09/2006

6 2. Substitution It is not possible to substitute the Mercury as it is naturally occurring in the gold bearing ore. 3. Engineering The gold room ventilation needs to be improved to assist in removing the Mercury vapour from the workplace environment. Original receptor hood curtains put back into place to assist ventilation (Figure 7). The ventilation fan has been increased in size. The receptor hood has been modified to ensure maximum extraction efficiency (Figure 8). Explore a retractable ventilation system. 4. Isolation Hazard barriers are placed at a 5 metre radius around the gold room on the day of a gold pour to restrict access to nonauthorised personnel. Shields/barriers need to be installed to isolate the gold room operator from the mercury vapour generated from the furnace while also assists to improve the ventilation efficiency (Figure 9). Shields/barriers create obstructions during the task of loading the furnace. Need to engineer a means of accessing the furnace without affecting ventilation (Figure 9). 5. Administrative No smoking procedures have been implemented to assist in reducing the operator s exposure to mercury vapour and elementary mercury. Hygiene procedures have been implemented to ensure appropriate hand washing is occurring before meals are eaten. 6. Protective Additional PPE has been implemented in the form of a P3 half face mask with a mercury canister. Task specific overalls have been issued and are laundered on site. N/A Ventilation may still not be sufficient to adequately clear mercury vapour causing the receptor hood to be overloaded and disperse into the work environment. Monitor workplace environment readings during trial stages. Security becomes a major issue when shields/barriers reduce visibility within the gold room blocking the view of the surveillance cameras. If trials successful consider retractable hood/barrier. Relies on the operators conforming to the procedures. Provide awareness training and monitor compliance through adequate supervision. PPE is a last line of defence and can easily be breached due to facial hair or incorrect fitting. Provide awareness training and monitor compliance through adequate supervision and ensure operators are conducting a fit test. As a result of the above recommendations under engineering and isolation a trial was conducted to assess whether the fume extraction system had the capacity to capture all air- Prepared by David Champion Page 6 of 9 29/09/2006

7 borne contaminants during the smelting process and whether a sufficient barrier could be created between the operator and the furnace. For the trial, modifications (Figure 8) were made to the original hood (Figure 7) and a temporary wall was constructed around the furnace (Figure 9) to reduce the short circuiting of airflow generated from the furnace and create an isolation barrier. The trial showed a reduction in the levels of mercury vapour recorded in the gold room area and verified that the extraction system did have the capacity to remove all of the fumes and isolate the operator from the mercury vapour. A retractable shield (Figure 10) was then designed to take into consideration the additional security surveillance issues highlighted in the above recommendations. Figure 7 - Original Hood Curtain Figure 8 Hood Modifications Figure 9 - Trial Modifications with Barriers 5. Figure 10 Final Modifications Full Length Retractable Hood BENEFITS / EFFECTS Testing of worker exposure to mercury vapour in the gold room environment before and after the upgrade using sampler badges has shown significant reduction in the Occupational Exposure Limit (TWA) levels in the gold room from mg/m3 mercury before to 0.007mg/m3 mercury after (Figure 11). Prepared by David Champion Page 7 of 9 29/09/2006

8 Static Monitoring for Mercury in Gold Room Pre the upgrade Post the Upgrade Hg (mg/m /05/2006 4/09/ /09/ /10/ /11/2006 6/12/2006 Access Door Evap Cooler Weigh up bench Operator Figure 11 Mercury TWA Levels (Button Monitors) Mercury vapour readings were also measured using a Jerome Vapour Analyser highlighting a significant reduction in mercury vapours inside and outside the gold room area (Figure 12). Mercury Vapour Readings - Post Furnace upgrade Hg (mg/m3) Outside Gold Room door Furnace Discharge Furnace Feed end Furnace Burner Office Breezw ay Shield Dow n Shield Up Figure 12 Mercury Vapour Readings (Jerome Meter) 6. TRANSFERABILITY ACROSS INDUSTRY The solution used to deal with the mercury vapour issue at NPO can easily be replicated within other industries where furnace vapours are presenting a risk to health of workers. The retractable shield allows improved ventilation efficiency and easy access to the furnace when required and does not present further risk to workers health through handling. 7. INNOVATION The retractable furnace shield was designed and installed to utilise the existing hood located above the furnace. The shield is a curtain constructed of flexible heat resistant material and Prepared by David Champion Page 8 of 9 29/09/2006

9 has been attached to the existing hood using a system of counterweights allowing the shield to be easily retracted for access to the furnace for loading and pouring. The counterweights eliminate any potential manual handling risks created by the handling of the new retractable curtains. Figure 13 - Shield in Up Position Figure 14 - Shield in Down Position 8. CONCLUSION As a result of the innovation implemented at NPO the level of risk to the gold room workers from the workplace airborne contaminant Mercury has been significantly reduced without the introduction of any new hazards. 9. REFERENCES Health Safety Executive, [HSE]. (2002). Method for the Determination of Hazardous Substances. COSHH Regulation [MDHS 16/1]. UK. Mines Occupational Safety and Health Advisory Board, [MOSHAB]. (2001). Management of Exposure to Inorganic Mercury in Gold Plants: Guideline. Department of Industry and Resources. Government of Western Australia. Mines Occupational Safety and Health Advisory Board, [MOSHAB]. (1997). Biological Monitoring: Guideline [Document No: ZMR7741Y]. Department of Industry and Resources. Government of Western Australia. Mining Safety and Administration, [MSHA]. (1997). Controlling Mercury Hazards in Gold Mining: A Best Practices Toolbox. US Department of Labour. National Institute of Occupational Safety and Health, [NIOSH]. (1999). NIOSH Pocket Guide to Hazardous Substances. [DHHS (NIOSH) Publications]. National Occupational Health and Safety Commission, [NOHSC]. (1995). Exposure standards for atmospheric contaminants in the occupational environment [NOHSC: 3008 (1995)]. Canberra: Australian Government Printing Service. World Health Organisation, [WHO]. (2003). Elemental Mercury and Inorganic Mercury Compounds: Human Health Aspects. Agency for Toxic Substances and Disease Registry (ATSDR), Atlanta, Georgia, USA Prepared by David Champion Page 9 of 9 29/09/2006