Central Refrigeration Service - Executive Summary
Central Refrigeration Service (CRS) provides installation and set up service for portable refrigeration units that are used to remove field heat from fresh harvested vegetables. The harvest season in Yuma is from mid-October through the end of April. During the harvest season refrigerant from the two storage vessels at CRS is transferred to the working refrigeration systems. The vessels are empty through part of the harvest season. |
Maintenance is performed on the vessels while they are empty. New pressure relief valves were installed in February 1999. A vapor compressor and 4-way valve system provides the means to transfer refrigerant to / from the vessels. The compressor and hose system is inspected for damage and wear and tear regularly.
Maintenance work is performed by Western Precooling Systems (WPS). WPS has four persons on staff in Yuma who have been trained to 1910.120(q) technician level by the Ammonia Safety & Training Institute and other training professionals. Eme
rgency Response equipment at WPS include chemical resistant suits and SCBA's as well as other emergency gear.
Access to the tanks is limited by fenced enclosure of the property. The tanks are in a protected area, covered with shade to minimize the exposure to radiant heat from sunlight. Traffic barriers are in place to discourage vehicle traffic at the tanks. In 1997 a water system was installed to help cool the tanks on extremely hot days (120 degrees F+) which provides effective evaporative cooling of the tank skin which reduces the pressure in the vessel.
WPS participated as observers in a Yuma Country LEPC disaster training excercise in February 1994 and provided training for the Yuma Fire Department in 1996 regarding response to illegal drug manufacturing labs using ammonia as part of the drug production process.
The storage vessel system at CRS differs from other storage systems (fertilizer terminals) in this way. The transfer activity takes place during a few weeks per ye
ar whereas a typical terminal will have daily transfer activity. We feel that these minimum transfers provides a plus in regard to risk and exposure.
The worst case scenario predicts a toxic endpoint of 2.7 miles (using Aloha). The simulated spill is from the larger vessel at 80% full. The facility is outside of the city in a rural setting, neighboring properties are cold storage and cooling facilities. The prevailing winds takes the plume away from the population. In order to achieve the 10 minute release factor we had to simulate a 4' crack in the bottom of the vessel. The largest nozzle on the vessel is 2" and would need 28 minutes to release the 80% volume of worst case situation. The 2" nozzle is protected with an excess flow valve which is proven to work when transferring from the vessel. A worst case situation will be very difficult to experience.
The alternative scenario depicts a relief valve lifting and failing to re-close causing the cooling of the liquid in the ta
nk to a point where the vapor pressure is zero. The situation that would exist to cause a relief to lift is from sustained 115 degree temperature in Yuma. The pressure in the vessel raises and falls with the product temperature which is affected by the ambient conditions. The quantity of refrigerant required to be released to get that refrigeration effect 12,264 pounds with a release rate of 264 pounds per minute. The duration would be 44 minutes. With a 3 meter wind the toxic endpoint is .25 miles.