Ammonia Release | Arc Flash in Solenoid Valve
Summary
In September 2022, a solenoid coil grounded out against the plunger tube which burned a hole in the post of the valve. This resulted in two injuries and a release of approximately 1,095 lbs of ammonia.
Incident Description
Damage to the solenoid coil allowed the “live” coil to make contact with the “ground” terminal inside the valve. This sudden spike in voltage created an arc flash inside the valve. The arc flash burned a hole in the armature, which allowed the ammonia to escape through the valve.
Release Calculation
The size of the hole was measured in order to determine how much ammonia was released. Below are the assumptions and analysis from the release calculation.
Significance
The root cause of the release was determined to be a failure/malfunction of the valve. Even when a system is well-maintained, mechanical failures can, and do, happen. Facilities should consider the location of valve groups in the event that a malfunction were to occur.
For example, evaporator valve groups are occasionally installed inside refrigerated spaces next to evaporator coils. If one of those valves malfunctions and causes a release, the ammonia would release indoors where employees may be exposed. Furthermore, accessing the isolation valves to mitigate the leak may be difficult. Valve groups located extremely high, or above stacked pallets/products may not be accessible with a lift or ladder in order to stop the leak. Ammonia refrigeration facilities should consider relocating valve groups from inside refrigerated spaces, to the roof where they are more accessible during a leak.
What amperage fuse was protecting this? 1 or 2 amp is more than enough. I’ve seen 10 amp fuses installed because they “keep blowing” which will turn the coil into a chunk of charcoal.
I’m not sure, but I appreciate your insight. A lot of the information we gathered came via the refrigeration contractor who diagnosed the situation and provided their assessment of the cause. They did not say specifically what the fuse rating was, but what you suggested seems credible.