PSM/RMP Lessons Learned
- The near disastrous anhydrous ammonia release in Central CaliforniaThe PSM/RMP LESSONS LEARNED reported in this month's newsletter come from a small ammonia refrigeration company in the Central Valley of California. The most significant events associated with the anhydrous ammonia release are listed below.
The anhydrous ammonia refrigeration system is about 25 years old. The engineer was an old timer, with many years of hands-on experience at this plant.
For a couple of months, the liquid level in the receiver had been going down. The engineer had noticed this loss, but could not find a reason why. He had checked for leaks, but had not found any.
Slowly he lost cooling capacity in his process coolers. He decided that the reason for this loss of efficiency and capacity was the lack of refrigerant being supplied to the evaporators, since the liquid level was low.
Still unable to find a reason why the liquid level was low, the engineer ordered a load of refrigeration grade ammonia from his supplier. This (he thought) would bring his level back up in the receiver and hence provide more liquid to the process evaporators.
The ammonia supplier arrived and loaded the main receiver to the level requested by the engineer, about two-thirds. The supplier completed the job and was just about to leave the site when the relief valves for the main receiver popped-off. This caused a release large enough to evacuate the facility and some neighbors. The Fire Department Hazmat team responded to the incident.
The engineer, with the assistance of the ammonia supplier, discovered that the receiver was full and over pressure in the receiver had caused the release. With the assistance of the Hazmat team, the supplier was able to remove some of the excess liquid ammonia to lower the level in the receiver to the desired two-thirds level. The supplier ended up removing nearly all he had originally installed.
The reason for the loss of liquid level and the loss of capacity was a partial blockage in the process evaporators causing liquid ammonia to back-up and log in the evaporators. The blockage chose that moment to open up, probably caused by the additional liquid pressure provided by the higher liquid level.ported that this plant engineer had no formal schooling or documen-ted technical certification. They suggested that he join RETA to get that necessary education.
PSM/RMP FAILURES
- SOP’s written to PSM/RMP standards would have provided the operator with guidance and instruciton that could have prevented an ammonia release.
- A Process Hazard Analysis (PHA) conducted to PSM/RMP would have identified system modifications that could have prevented an ammonia release.
- A documented training program meeting PSM/RMP requirements would have prepared the operator with system understanding that could have prevented an ammonia release.
- And many more PSM/RMP prevention requirements apply.
Our small California refrigeration company was “lucky”. No one was injured, there was no law suit, and no regulatory agency compliance audit was ever conducted. You can depend on a quality PSM/RMP program to minimize the potential for a release - you can’t depend on “luck”.
