Secondary cause of fatal ammonia leak

27/07/2018

A leak in the secondary brine coolant system caused the fatal ammonia release at the Fernie ice rink last year that killed three people.

The report into the incident, released yesterday by Technical Safety BC, makes 18 recommendations to improve safety in ice rink refrigeration systems, and discusses a number of regulatory actions taken in recent months to prevent similar incidents. 

In addition to the failure of refrigeration system equipment, the report pinpoints inadequate ventilation and discharge systems and operational decisions as being contributing factors leading to the incident.

Technical Safety BC says the incident is believed to be the first of its kind in which a leak of ammonia into a secondary coolant – in this case brine – led to pressurisation in a pipe that resulted in the pipe coupling separation and a rapid release of ammonia into an enclosed room.

The Fernie Memorial Arena operated a two-pass flooded refrigeration system providing cooling for two brine secondary systems – one cooling the arena floor, and the other cooling the curling rink floor.

The curling brine chiller at the Fernie Memorial Arena had been put back into operation on October 16, 2017, after a seasonal shutdown. During the shutdown and seasonal maintenance, ammonia had been detected in the curling brine system, indicating that the curling brine chiller was leaking.

The investigation found that the ammonia release was initiated by a small hole, measuring around 2.2mm x 0.2mm, within the curling system brine chiller caused by corrosion pitting at a carbon-steel tube welded seam. It is not known when the chiller entered into service but is known to have been manufactured in 1986.

At 03.53 on October 17 an ammonia alarm in the arena’s mechanical room was triggered and the system was shut down. This impeded brine expansion and ventilation, as ammonia continued to leak into the brine over a five hour period. As the leak continued, the concentration of ammonia would have become higher close to the chiller and the hole in the tube. The report finds that the likely effect within the brine system near the chiller was: an ammonia saturated volume of brine; a temperature increase from chemical reaction and heat absorption from the room; elevated pressure within the brine system and chiller; and a displaced volume of brine from ammonia being added to the saturated solution.

A brine system pipe segment was joined at two locations near the chiller by pipe couplings that were not supported to resist pipe movement from pressure or mechanically applied forces. The rising pressure within the brine system eventually exceeded the strength of the joint and one of the couplings separated. Around 9lb of ammonia was rapidly released into the plant room, followed by additional ammonia from the system. It is estimated that the concentration of ammonia in the plant room may have reached or exceeded 20,000ppm.

A total of three people were subsequently found dead in the plant room: the director of leisure services, the refrigeration operator, and a refrigeration mechanic.

Responders opened the emergency discharge valve and pressed the emergency stop for the ammonia system located on the exterior wall of the arena. Opening the discharge valve resulted in an estimated initial release of 55lb of ammonia into the atmosphere with approximately 632lb of ammonia from the system being slowly released during the subsequent days.

Due to the three fatalities, the ammonia release and the unknown amount of ammonia remaining in the arena, the City of Fernie issued a local state of emergency and evacuated approximately 55 homes and 95 residents from the surrounding area.

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