Acme Ice Company - Executive Summary |
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Acme Ice Company is a manufacturer of ice for wholesale and retail sale. As such, the company operates two mechanical refrigeration systems, using anhydrous ammonia as the refrigerant. The first system, the smaller of the two, was installed in 1930, to make block ice. The system capacity for ammonia is less than 8,000 lbs, and thus is below the threshold for inclusion in the Risk Management Plan. This system is completely separate from the larger one, and has no interconnecting piping. The degree of physical separation between this and the larger system makes it virtually impossible for a disaster in the small system to affect the larger system. The second system was installed in 1990, to make cube ice. The system capacity for ammonia is 19,000 lbs, most of which is stored in the receiver and ice-makers. The degree of physical separation between this and the smaller system makes it virtually impossible for a disaster in the larger system to affect the small system. Acme Ice Co mpany has long been committed to employee safety and to being a good community neighbor. To this end, Acme maintains an active safety management program to prevent accidental releases of ammonia. The facility complies with OSHA's PSM rule, and maintains a written Process Safety Plan onsite. A rigorous program of operator training, preventive maintenance, and periodic internal inspections is maintained, to prevent the accidental release of ammonia, and all required safety programs are in force at the facility. In the last five years, there have been no reportable releases of ammonia, and no accidents involving the release of ammonia. All ammonia is stored in the refrigeration systems, and there is no additinoal storage on-site. The facility is located in a residential section of the City of Chicago, approximately 3.5 miles south of the Chicago Sanitary and Ship Canal, and 3.5 miles east of MIdway Airport. The setting is urban. The worst case scenario is considered to be the rupt ure of the high-pressure receiver, which contains most of the ammonia at any given time. It is considered that this rupture would cause loss of all the ammonia in the system over a period of 10 minutes at a constant rate. The toxic endpoint is taken to be an ERPG-2 of 200 ppm for an exposure time of one hour, and was estimated at 2.6 miles from the source. The consequences are modeled in atmospheric stability category F weather conditions with a windspeed of 1.5 m/s. These assumptions are taken form the "Model Risk Management Program and Plan for Ammonia Refrigeration", prepared by Science Applications International Corporation, Reston, VA. These assumptions were adopted because of the significant cost of doing modeling studies that are site specific, and because the final conclusions were not likely to change significantly even though site-specific information was used. This scenario has off-site receptors. There are no active mitigation systems in use. The building enclosure was considered and dismissed as a passive mitigation system, as the enclosure is of a construction not expected to withstand a 1 psi overpressure that is likely to occur on rupture of the high pressure receiver. The alternative scenario, one more likely to occur, is a gasket rupture or pump seal leak equivalent to a small orifice of diameter 1/4 to 1/2 inch. A typical rate of release would be 100 pounds/minute. Atmospheric Stability Category D with a moderate windspeed (e.g., 3 m/s) was chosen from the model. The toxic endpoint of 450 feet was chosen from the model plan as typical of an urban site, and the smallest rate of release which would have off-site receptors. This alternate scenario has off-site receptors. Passive mitigation to a release of 100 pounds/minute is considered to be the building in which the high pressure rceiver and process piping is housed, because such a release would not be expected to inflict structural damage on the building housing the receiver. Such a release could be contained until automatic and manual shutoff systems could be activated. Responders could further mitigate the release by absorption in water from a fire hose, and neutralizing the resulting aqueous mixture with acids, or releasing the solution to the sewer. Acme Ice Company personnel are trained to respond to minor releases and minor repair/maintenance problems. However, for a major release, the facility would call upon the Chicago Fire Department for emergency response. Facility personnel are trained in response actions which consist of minimizing damage to the facility while assisting the orderly evacuation of all personnel. Acme Ice Company regularly evaluates and implements any appropriate measures to further improve safety. |