CYPRUS SIERRITA CORPORATION - Executive Summary
THE ACCIDENTAL RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES AT YOUR FACILITY. |
Each employee of Cyprus Sierrita Corporation (CSC) is provided with a General Safety and Environmental Handbook. In the handbook, the corporate (Cyprus Climax Metals Company) and site-specific (Cyprus Sierrita Corporation) Safety and Health policies are presented. The policies are included with CSC's Risk Management Plan submittal.
CSC has an excellent record for safety and lost-time accidents. In 1998, CSC received the most prestigious award in the mining industry, the Sentinels of Safety Award. The Sentinels of Safety Award is cosponsored by the American Mining Congress (AMC) and the U.S. Department of Labor's Mine Safety and Health Administration (MSHA) for recognition of achieving one of the best records for number of employee work-hours in 1997 without a lost-time injury or fatality.
YOUR FACILITY AND THE REGULATED SUBSTANCES HANDLED.
CSC operates a copper and molybdenum mining and concentra
ting facility located approximately seven miles west of Green Valley, Arizona. Ore containing low-grade porphyry copper and molybdenum deposits, is excavated, crushed, conveyed, milled and concentrated to produce a separable copper and molybdenum concentrate slurry. A final flotation and conditioning process is used to separate the copper minerals. The copper sulfide product is filtered and shipped to a smelter by either truck or rail for further concentrating. The molybdenum sulfide concentrate is filtered to produce a damp cake, which is dried and stored for further processing.
The final molybdenum sulfide concentrate still contains a small percentage of copper, which cannot be effectively removed using the final flotation process. The copper content in the molybdenum concentrate can be significantly lowered using a ferric chloride leach process. A hot ferric chloride solution is agitated in a series of mixing tanks with the moly concentrate. The slurry exiting the last tank
is a high-grade molybdenum sulfide concentrate. The copper leached from the process is recovered as cement copper and sent to a smelter for further processing with the copper concentrate.
The ferric chloride leach liquor is recycled and regenerated using chlorine and iron scrap. A 90-ton railroad tank car of chlorine is connected to each of the two 7,000 gallon chlorination tanks. Typically, two back-up chlorine railcars are stored near the chlorinator area at the west-end of the rail line and/or by the copper concentrate storage area near the mill maintenance shop. The maximum number of railcars anticipated on site at any one time would be seven. Each chlorine railcar provides approximately a seven-day supply of chlorine for the chlorination process.
The separated molybdenum sulfide is roasted to yield a molybdenum trioxide, which is packaged for distribution.
Eleven propane tanks, ranging in capacity from 500 to 30,000 gallons, are located throughout the Sierrita and Twin But
tes Properties for building and process heating. Program 1 requirements for propane under the RMP were triggered due to two 30,000- gallon propane storage tanks located east of the administration building. Currently, only one of the tanks contains propane at 50% of its nominal capacity. The propane in these two tanks is stored for use as an alternative fuel to the molybdenum roaster process. The tanks are to be kept at their current storage capacities unless deemed necessary.
A pure or propane blended fuel source is required for the conversion of molybdenum sulfide to molybdenum trioxide. In the event of a loss of CSC's current molybdenum roaster fuel source, propane would be used to maintain the temperature in the molybdenum roasters to avoid equipment damage.
THE WORST-CASE RELEASE SCENARIO(S) AND THE ALTERNATIVE RELEASE SCENARIO.
Using the DEGADIS (Dense Gas Dispersion) modeling program, the worst-case release and alternative release case scenarios for propane and chlorine
The worst-case release scenario for chlorine was defined as the release of 90 tons of chlorine from the railcar storage vessel over a ten-minute period. This assumption provided a release rate of 18,000 pounds per minute. The DEGADIS model predicted that the chlorine toxic endpoint for this release would be reached at a distance of approximately 22 miles (116,153 ft) from the railcar. No passive mitigation devices were considered in this analysis.
The chlorine alternative release scenario was selected to be a rupture of the chlorine transfer line from the railcar storage vessel to the chlorination tank. Because the railcars have check valves that are automatically actuated by a sudden pressure drop, it was assumed that such a rupture may release chlorine for no more than five minutes. From the DEGADIS model, the toxic-endpoint distance was determined to be approximately 1.55 miles (8184 ft) from the railcar.
The worst-case release scenario for propane would be a
release of approximately 63,600 pounds of propane from storage tanks located east of the administration building. From the DEGADIS Offsite Consequence Model, the impact of the worst-case release would be a distance of 0.323 miles (1705 ft). The distance of the propane tanks to the property boundary is 0.417 miles (2202 ft). Therefore, the worst-case scenario for propane would not effect public receptors within the distance to the endpoint from a worst-case release.
THE GENERAL ACCIDENTAL RELEASE PREVENTION PROGRAM AND CHEMICAL-SPECIFIC PREVENTION STEPS.
CSC is regulated by the Mine Safety and Health Administration (MSHA). Every six months, MSHA performs a comprehensive inspection of CSC's facility for compliance with the Federal Metal and Nonmetallic Mine Safety and Health Standards listed in the Federal Code of Regulations (CFR), 30 CFR, Parts 1 to 199. The role of the MSHA is to enforce compliance with 30 CFR, Parts 1 to 99 as a means to eliminate fatal accidents; to reduce
the frequency and severity of nonfatal accidents; to minimize health hazards; and to promote improved safety and health conditions in the Nation's mines.
Several mitigation devices are located in the chlorination area to prevent a chlorine release from occurring. Five chlorine sensors are located around the perimeter of the chlorinator area for identifying the presence of chlorine. The sensors are capable of detecting chlorine in concentrations greater than or equal to 1 ppm. If a release is sensed, the latching relays are de-energized and the two valves from the railcar and the automatic addition valve close. The valves are set up to fail in a closed position in the event of a power or air supply loss. In addition, all of the railcars supplied by Pioneer Chlor Alkali, CSC's chlorine supplier, are equipped with check valves, which cut off the chlorine supply if the flowrate were to increase rapidly.
In addition to the mitigation devices described above, a main chlorine shut-off de
vice can be triggered to cease chlorine supply by manually hitting a "red button" located in the Moly Control Room.
The chlorination process is also equipped with an absorption system to prevent over-chlorination of the process, which may result in a chlorine release. The absorption system consists of a 265-gallon tank containing an 18% caustic soda solution. Chlorine in excess of the process required amount is vented to the chlorination tank, where it is neutralized. The tank is emptied daily and recharged by the Moly Utility Crew.
Monthly tank inspections are performed for each of the storage tanks in the chlorination area and for each of the propane tanks as part of CSC's preventative maintenance program. The inspections are used to monitor any signs of tank deterioration, leaking and corrosion of tanks, valves and all associated piping. Secondary containment structures, if applicable, are also inspected for stability, leaks, and fluids present in containment structures.
HE FIVE YEAR ACCIDENT HISTORY
CSC has had no chlorine releases in the past five years requiring medical treatment other than minor first aid. As a safety precaution, CSC requires first aid for any and all types of chlorine releases, regardless of the extent of the release. There have been no reportable releases and no environmental impacts from chlorine releases.
CSC has had no propane releases in the past five years.
THE EMERGENCY RESPONSE PROGRAM.
CSC has established an Integrated Contingency Plan (ICP) which addresses general and chemical specific emergency response procedures. Recently, a detailed Chlorine Emergency Response Plan was added to the ICP. Chemical specific emergency response procedures for incidents involving propane were also incorporated into the revised ICP. The ICP and all subsequent revisions are sent to the Pima County Local Emergency Planning Community, Green Valley Local Fire Department, Arizona Emergency Response Commission and St. Mary's Hospital for l
ocal emergency response coordination.
In the event of a chlorine release, an audible alarm will sound. Evacuation routes have been developed and are posted throughout the Moly area and are in the ICP. The site has several trained first responders and a spill response team to respond to safety and environmental incidents.
PLANNED CHANGES TO IMPROVE SAFETY.
There are several changes being completed to the chlorination area that will improve safety and prevent the possibility of a release from occurring:
1. A chlorine remote video monitoring system has been purchased and is scheduled for installation by August 1999. The system will be installed in the Moly Control Room and allow the operator(s) to monitor the loading and unloading of chlorine railcars. If an incident involving chlorine were to occur during the loading / unloading process, the operator could quickly cease the chlorine supply from the control room.
2. An expansion bottle will be installed between two block valv
es in the chlorine piping system. The expansion bottle will prevent liquid chlorine from becoming trapped between the two block valves, if closed. The estimated completion for this item is early July 1999.