The Natural Refrigeration

Are you aware of changes that happen around you? When a smell changes, or a sound changes, etc. are you so focused on your work or another activity that you don’t even notice?

There are five primary senses. Smell, hearing, sight, taste, and touch. However, we actually have considerably more. Researchers have identified approximately 22 to 33 different senses. These additional senses are internal and specialized senses like balance, temperature, pain, proprioception, etc. As we become more aware of the many inputs we have we can be better equipped to make good decisions.

Unfortunately, many times people tune out the primary senses. This is one reason you should not text and drive. When we do tasks such as this it is sometimes referred to as “tunnel vision”, although it is not a problem with the eyes, it is a mind issue.

Our minds can switch between tasks but not do two tasks simultaneously. When we are focused on a task, information coming to us that may be important is most often ignored. We all should be more aware of changes. The following is an example of a lack of awareness that lead to an ammonia release.

It likely started with a small vibration as a composite blade on multi-fan evaporator fan motor cracked. Why the fan blade began to fail is unknown. Composite blades (glass reinforced polypropylene) are used on thousands and thousands of evaporators, with an extremely low rate of failure.

They are very reliable. The personnel working in this particular storage room were focused on their task of driving forklifts as they loaded produce into a room. The evaporator fans were already noisy, and the forklift drivers apparently did not notice a change in sound. How long the crack in the blade had been growing is unknown but eventually the blade completely failed, meaning it separated from the hub of the fan assembly that was attached to the fan motor shaft.

When this happened the 3-blade fan was out of balance which caused additional stress on the other two fan blades. Eventually a second blade failed, which definitely would have been a noticeable sound change. Now the unit had serious vibration that affected not only the fan motor and its base, but the entire evaporator.

How long this condition went on is also unknown, but the forklift drivers either didn’t notice or didn’t realize this was significant and the refrigeration operator(s) should have been notified. The refrigeration operators, during their daily rounds, should also have noticed this change in both sound and vibration but did not.

It may have been possible for the crack in the blade to be seen during the annual evaporator inspection, but this didn’t happen. Any slight change in the sound of the unit during operation would, due to a slight crack in a blade, likely not have been noticed, especially with several other noisy fan motors operating on this same unit. With two blades missing, the sound change was very noticeable.

With the failure of the second blade, still no one noticed the difference in sound of the fan nor the sound of the entire evaporator which was now vibrating. The movement of the unit was so significant that the vibration traveled up the ammonia refrigerating piping to the surge drum located above the roof in a small room, called a “doghouse”. This vibration may have been going on for days, weeks, or longer. It was later seen that the vibration had caused a crack in the motor mounting base of the fan.

A much more significant impact happened in the doghouse. The surge drum relief connection came out of the center of the head of the horizontal vessel. The relief line was piped out through the vessel insulation and turned 90 degrees and extended a few inches to connect to the 3-way relief valve.

The outlets of the associated relief valves joined together to extend outside of the doghouse. It was and typically is a screwed connection into a 3-way valve.

As time passed and the vibration continued, the pipe coming into the 3-way valve not only cracked but completely separated from the 3 way valve. When this occurred, there was a ½” schedule 80 pipe releasing ammonia vapor inside the doghouse. The leak started in the early morning hours.

The facility had a computerized control and alarming system for the refrigeration. The first alarm notified the refrigeration operator(s) that the system had shutdown due to a high liquid level in the suction accumulator. A second alarm occurred due to ammonia getting into the room below the doghouse.

On arriving the two refrigeration operators that responded first checked the machine room. They noticed that the float switch arm was away from the float head column, indicating that no liquid was present at the float activation level. Not seeing any problems in the machine room, they headed to the roof of the facility. As they approached the access ladder to the roof level where several doghouses were located, they started to smell ammonia.

They decided to return to the machine room and close the manual king valve as a further precaution even though there was an electric solenoid (King solenoid) that had already closed due to the high liquid level alarm. They then returned to the roof.

As they got close to the doghouse they heard a loud noise caused by ammonia vapor releasing through the sheared ½” relief pipe. They wisely decided to remain outside of the doghouse and after a short time noticed the sound starting to dissipate. When the sound stopped they carefully opened the doghouse door to allow the small doghouse to better vent.

As these events were happening another very important action for an ammonia release was taking place. When the ammonia alarm was received one of the refrigeration operators called their supervisor alerting him to the ammonia alarm. He headed to the facility and while on the way called the National Response Center (NRC) and reported that they had a release going on of ammonia, and at that time, it was an unknown amount; also, that no one was injured.

He next called the state. The state was already aware of the incident having been alerted by the NRC, but he still made a similar report of the event. He also tried contacting the Local Emergency Planning Committee (LEPC) but due to the time being well before 8 am he left a voice mail. He also called the Fire Department just to inform them. The Fire Department decided to send an engine to the facility as a precaution.

The Chemical Safety Board (CSB) was also supposed to have been notified within 30-minutes of contacting the NRC. This was actually done later in the day but there was no additional information the facility could report. Whether the loss of product was significant or not would not be determined until many days later.

The result was that there was a significant loss of product due to the contaminated ammonia vapor in the room. The amount of ammonia released was a few times over the 100 pounds in 24-hours, so it was appropriate and good protocol to contact the NRC, CSB, State, LEPC, and the Fire Department. Repairs were made and the system put back in operation.

It is likely that this whole incident could have been avoided if someone had noticed the change in sound of the evaporator and appropriate actions had been taken. The refrigeration operators need to be made aware of changes in sounds, smells, vibrations, etc. in their system(s) from other personnel who notice such changes or due to their own observations.

People working in facilities should also be aware and know who to contact, so an issue can be addressed before it becomes an incident. We all need to be more aware of what is happening around us and not miss the cognizance that something significant may be occurring.