Lesson Learned: Bad Decommissioning Mistake

I am sure that many of us have seen ammonia refrigeration systems that have operated for several decades, with equipment and system components functioning well past recommended operating life. This is a credit to manufacturers, installers, service technicians, and operators. Aging equipment and piping at some point will eventually require replacement. Or the system or portion of it may be decommissioned due to a business discussion. Due to various conditions, it may become necessary to decommission a system or portions of it, which is defined in ANSI/ IIAR 8- 2020 – Decommissioning of Closed-Circuit Ammonia Refrigeration Systems as: “The permanent deactivation of a closed-circuit refrigeration system.” ANSI/IIAR 8-2020 is a helpful guide when considering decommissioning some or all of an ammonia refrigeration system.

At some facilities equipment and piping may be abandoned in place for various reasons. This may occur due to the difficulty of removing the equipment and piping; the cost of removal is considered too high; or it may be abandoned in place because the unusable space taken up will not have an impact on the operation.

Whatever decommissioning is intended to be done many factors should be considered so the work is done safely. The slow decommissioning of two separate systems at a facility in Kamloops, BC actually began on December 21, 2015, when the equipment was shut down. On May 26, 2022, during the attempt to remove equipment associated with one of the systems, an accident occurred. It resulted in one fatality, ammonia ignition, 14 persons exposed to ammonia and 3 went to the hospital, a local evacuation, extended facility business shutdown, and an environmental response to the release.

In the Technical Safety BC report of the incident, one could see that a major contributing factor to the incident was a lack of and breakdown in communication. Since this demolition occurred over several years this made the need for clear and accurate communication and documentation of what had and hadn’t been done even more challenging. This is an important factor to consider if demolition will take months or years to get done.

The misunderstanding regarding the ammonia still being in the system occurred due to changes in personnel and their assigned responsibilities as well as a miscommunication of what work had been completed. The refrigeration mechanic familiar with the system had pumped down the two systems to their respective high-pressure receivers in 2016 before his retirement. He stated the ammonia was still in the system. The Distribution Manager also believed the ammonia was still in the system, however, the Plant Manager who had been relocated to another city thought it had been removed. It was not clearly communicated that the ammonia had not been removed from the system. From 2016 till May 25, 2022, it was incorrectly believed that there was no ammonia in either of the two systems.

The belief that there was no ammonia in either system should have been questioned when on May 25th a worker cut into an HPR pressurized ammonia line connection with a Sawzall. After this occurred the people involved supposedly reviewed the other system for indications of ammonia. Unfortunately, those doing the demolition did not understand what they didn’t know and still held to the belief that all the ammonia had been removed, which was one of their strict criteria before removing systems or system components.

It was assumed that the high-pressure receiver was empty because there was no liquid indicated in the liquid level sight glass, not realizing that the sight glass isolation valves were closed. They also believed that the system pressure gauges, that showed 0 psig meant the high-pressure receiver (HPR) must be empty. These gauges did not indicate HPR pressure. It was believed that the ammonia vapor released from the first system was just residual and could be quickly purged to continue the demolition.

While looking at the HPR piping of the second system it was assumed that because they saw a pipe completely open with no shut-off valve between the open end and the vessel, the vessel must have been empty. A review and understanding of whatever system piping diagrams that might have been available, as suggested in ANSI/IIAR 8-2020 Appendix B. (Informative) Example of a Decommissioning Checklist could have prevented the fatality. They should also have had help from a trained refrigeration technician or licensed contractor, but the added cost was an issue.

Once it was discovered that there was ammonia pressure in the one system that should have raised a concern in the mind of those doing this work. The demolition at that point should have stopped. A licensed refrigeration contractor should have then been involved to determine the system condition(s). ANSI/IIAR 8-2020, Chapter 5 recommends: “ Do not physically disconnect and remove system components until the components have been isolated and residual ammonia and lubrication oil have been drained from the components.” Unfortunately, this was not done.

After the discovery of ammonia pressure in the first system those doing the work decided to purge what they thought was residual ammonia from the system. It is estimated that the purging process took approximately 16.5 hours and purged the entire system’s ammonia operating charge, later estimated to be a maximum of 1,044 lbs.

On May 26 the removal of the second system components began. It was noticed that a valve stuck out past the support skid of the HPR so the assembly could not be laid on its side for removal from the room. The valve was a one-inch ¼ turn ball valve with no plug or cap in the exit of the valve. The valve was in the HPR liquid supply line and had an internal extension pipe that went to near the bottom of the HPR. The valve was turned ¼ turn which fully opened the line releasing pressurized liquid ammonia directly onto the person opening the valve and quickly filling the area with a dense cloud of ammonia. The other person was able to escape through a large front bay door, but the person hit by the ammonia moved further into the building. The dense cloud of ammonia came in contact with an ignition source and ignited. It was later estimated that 1,345 lbs. to 1,600 lbs. of ammonia had been released directly into the atmosphere.

The machine room area ventilation system had previously been shut off due to the mistaken belief that all the ammonia had been removed from both systems. It was later estimated that even with a functioning ventilation system due to the large and sudden release the ignition of the ammonia would likely still have occurred.

In the post-investigation of the incident, it was discovered that the pressure relief valve on the HPR involved in this incident had at some time in the past been removed. On checking the integrity of the isolation valves associated with all connections to the HPR it was verified that all could be closed securely tight, and the vessel would hold pressure. It was estimated that the HPR held 1,600 lbs. of ammonia which was the manufacturer’s recommended charge for that system. Fortunately, the ambient conditions never reached a temperature that would have expanded the ammonia contents of the HPR to cause a failure of the vessel, a connected line, or a valve.

Several factors contributed to this unfortunate incident. The misinterpretation and poor communication of whether the ammonia had already been removed from the system was a major factor. However, following the guidelines as given in ANSI/IIAR 8- 2020 – Decommissioning of Closed-Circuit Ammonia Refrigeration Systems would very likely have made this a non-event, saving someone’s life. Don’t make similar mistakes as occurred in this incident when decommissioning a system or equipment in a system.