Montana Sulphur & Chemical Company - Executive Summary |
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1.1 Regulated Substances Montana Sulphur & Chemical Company (MSCC) is a small business located in a heavy industry area northeast of Billings, Montana. MSCC operates a gas sweetening plant, a Claus sulfur recovery plant, sulfur solids and fertilizer plant, sulfide chemicals production facility, and product storage facilities . A review of the existing processes at MSCC has identified hydrogen sulfide (H2S) as the only chemical "inventoried on site" above the threshold quantities listed in the Code of Federal Regulations (CFR), Title 40, Part 68 and, therefore, subject to a Risk Management Plan (RMP). MSCC has handled compressed H2S daily in large quantities at the site since 1956. MSCC has produced and stored purified merchant H2S in above-threshold quantities since 1967. No injury to nearby members of the public, evacuation, or damage to property in the nearby community has occurred due to MSCC's production or storage of liquid H2S in above threshold quantities. While H2S is a w idespread, naturally occurring, substance ordinarily present in the human body as a result of digestion, and in the environment due to biologic and geothermal processes, it can be toxic at elevated concentrations. H2S is a byproduct of petroleum and gas refinering and has many uses. It is prudent to observe safety precautions in handling H2S to prevent unnecessary human exposure at harmful concentrations in order to reduce risk to health and safety of workers and to nearby members of the community. MSCC has been and is strongly committed to protecting the health and safety of employees and nearby members of the community from significant H2S exposure arising from the liquid hydrogen sulfide processing and storage facilities. Safety at MSCC depends upon the manner in which H2S is handled as well as various safety devices incorporated into the design of the equipment. Furthermore, training and experience received by MSCC employees adds to the inherent safety of the process. 1.2 The Wo rst Case Release Scenario and the Alternative Release Scenario As required by EPA, the worst case release scenario (WCS) examined a rapid release from the single largest capacity (74 tons) H2S storage vessel on site, under unfavorable dispersion meteorology assumptions. The WCS was a hypothetical release of the entire tank in 10 minutes at a wind speed of 1.5 meters/second (m/s) and an "F" stability class. As required by EPA, this scenario considered that prevention and mitigation techniques, responses, and devices at the facility did not exist or failed, and furthermore, the resulting release of intrinsically flammable gas does not ignite. These assumptions are considered highly improbable and unrealistic by MSCC. The alternative release scenario (ARS) is provided to meet the criteria of a release having characteristics of some off-site consequence, more representative meteorology, and somewhat higher probability of occurrence. As suggested by EPA guidance, the ARS looked at a rela tively large release from a hypothetical process piping rupture, with the contents of a relatively long pipe between an excess flow valve and a remote operated valve being rapidly released to the atmosphere. In this hypothetical case, 704 lbs of liquid H2S are released in ten minutes, again without ignition, at a wind speed of 3.0 m/s and a neutral "D" stability class, which is intended to represent more probable meteorology at the site. Some, but not all, of the prevention mitigation techniques, responses, and devices at the facility are presumed to fail to produce this alternative release scenario. The probability of this pipe rupture is considered remote. This alternative scenario has not occurred in the past history at MSCC. The distance to the EPA-defined "toxic endpoint" (30 ppm) for both scenarios were estimated using the EPA-issued software program called RMPComp, which is publicly available. The EPA-designated "toxic endpoint" for this material appears to have been set to co incide with the "no observable effects level" for H2S from a rodent study. It should be noted that this level is relatively low compared to concentrations of the gas known to occur naturally in the human digestive tract. The EPA concentration is also significantly lower than the long-standing OSHA daily short term exposure ceiling of 50 ppm and the current IDLH value of 100 ppm, both of which were established conservatively to avoid and/or minimize the effects of transient eye and mucous membrane irritation from acute (short term) exposures over time periods comparable to those involved with short term, accidental releases. The potentially debilitating or life-threatening effects associated with this compound over short periods of time arise from significantly higher concentration. As a result, it is apparent that the end-point distances projected by RMPComp extend considerably beyond the likely danger zone from the hypothetical release. The results of RMPComp were also compared with t he results of SLAB, a somewhat refined, yet conservative dispersion model used by EPA using the same "toxic endpoint" concentration. For the WCS, this modeling indicated a 30 ppm endpoint at a distance 25% less than the distances projected by RMPComp and a 67% decrease for the ARS. For these reasons, as well as from experience, MSCC must caution readers that the projected endpoint distance appears unrealistic. 1.3 The Accidental Release Prevention Program MSCC has taken necessary steps to comply with the accidental release prevention requirements set out in the RMP regulations. The H2S process is subject to OSHA Process Safety Management (PSM) regulations which parallel the prevention program in the RMP requirements, except for the need for an analysis of offsite impacts. MSCC has prepared a PSM plan for the H2S used on-site; the plan is referenced in this RMP and addresses the Program 3 prevention program for H2S. 1.4 Five Year Accident History MSCC has an excellent record of preventing significant accidental releases over the last five years. During this period, as determined by the RMP program guidance, no recordable accidental releases of H2S from the regulated process have resulted in deaths, injuries, or significant property damage on-site, or any known offsite deaths, injuries, evacuations, sheltering in place, property damage, or environmental damage. 1.5 Emergency Response Plan MSCC has a written emergency response plan to deal with the accidental releases of chemicals. The plan includes all aspects of emergency response including adequate first aid and medical treatment, evacuation, and communication with the local fire department, local emergency planning committee (LEPC), and through the agencies, the public. MSCC has contributed, along with several industries and agencies, to the installation of the County emergency siren system, which is used as part of the County's Shelter-in-Place program for hazardous material and other emergencies. T o ensure proper functioning, emergency response equipment is inspected and serviced, as necessary. In addition, the plan is updated, as required, to reflect any pertinent changes taking place within the H2S process that would require a modified emergency response. The emergency contact given in Section 1.8 is only for emergency response to releases. For information on the RMP emergency response planning, alternate contacts are currently Donald G. Zink, Larry Zink, Fred Bell, and Vern Luderman who may be reached at the phone number given in Section 1.9-b. 1.6 Planned Changes to Improve H2S Safety MSCC maintains an ongoing safety program to minimize accidental releases of H2S. This program includes employee training, preventive maintenance, hotwork permitting, lockout tagout procedures, vessel entry procedures, respirator training, and safe handling/operational procedures of the H2S process. Safety with H2S is a major concern and an ongoing process at MSCC, and improvements in saf ety are updated and implemented on an as needed basis. |