Ammonia Release | Tarp vs. Fan vs. Coil

Summary

In May 2021, a three-inch strip of tarp was sucked into a lower bunker fan for a postcooler room. Two fan blades broke and flew into the bunker evaporator coil, resulting in a release of approximately 4,600 lbs of ammonia. 

Incident Description

The postcooler room is equipped with a bunker that contains two evaporator coils that are supplied by a single accumulator. The evaporator coils are installed above the fans that circulate air through the coils. 

Inside the room, a small tarp is used to wrap product pallets to produce more efficient cooling. A small piece of tarp was able to slip through the fan guard and was sucked into the fan. Two of the fan blades broke and flew upwards into one of the bunker evaporator coils. The fan blades punctured two holes in the coil which caused the release.

Release Calculation

The amount of ammonia released from the system was calculated based on the normal operating level in the high pressure receivers. The system is equipped with two (2) high pressure receivers which are interconnected. The normal liquid level inside the two vessels is 36 inches. After the release, the liquid level in the high pressure receivers was measured at 28 inches. The table below illustrates the amount of ammonia released was estimated to be 4,600 lbs.

Vessel	36” Liquid Level	28” Liquid Level	Liquid Level Drop
High Pressure Receiver 1	7,772.9 lbs	5,906.1 lbs	1,866.8 lbs
High Pressure Receiver 2	11,417.5 lbs	8,683.6 lbs	2,733.9 lbs
Combined Total	19,190.4 lbs	14,589.7 lbs	4,600.7 lbs

Significance

Even though fan guards were in place, this did not prevent the tarp from becoming stuck in the fan. The incident prompted a recommendation to either change the tarp size/design, or to improve the fan guard design in order to prevent the accident from recurring. Facilities should consider the proximity of stacked pallets to fans and ensure fan guarding is adequate.