Executive Summary:
Minor non-permanent injuries (to two operators), and more severe injuries to a third employee resulted when ammonia refrigerant vapor was released from a safety valve on the outdoor refrigerant condenser. Equipment failure, ambient conditions, inadequate staff training contributed. A certificate of inspection was issued with follow-up. A complete plant survey was conducted and additional certificates of inspection issued.
Full Description of Incident:
At shift change, an uncertified day shift operator was made aware that two ammonia refrigeration compressors had been short-cycling from 0400 Hrs (low suction pressure). The operator then opened the suction by-pass valve to a second chiller. Both ammonia compressors started then quickly tripped. The operator resets both high-pressure limits. This process was repeated. The ammonia condenser safety valve lifted, and when the operators walked outside to investigate they both walked into ammonia vapor. Fire and police responded to evacuate the facility, and paramedics examined the operators. A third compressor continued to cycle and lift the safety valve for 1 hour (400 lbs of ammonia released) until the hazmat team arrived and shut down the plant at the fire box. Condenser pump control failure, ambient conditions (low temp/high relative humidity) and inadequate staff training contributed.
Multiple certificates of inspection were issued, with follow-up.
PV128257 (NH3 evaporator condenser) Baltimore Air Coil; model VC1-205R;MAWP 250psi; 1997.
RU8R035 (refrigeration unit -indirect closed surface): Mycom; model N6AM; AWP 250psi.
Summary of Damages, Injuries, Fatalities:
Minor non-permanent injuries to two operators, and more serious injuries to a third employee (mucous membrane, eyes, ears and respiratory system were affected). Approximately 400 lbs of ammonia refrigerant was released to the atmosphere [400 lbs @ $1.75/lb = $700].
People Involved:
Number of People Injured: 3
Number of People Deceased: 0
Cause Summary:
Condenser pump controller (Johnson Controls/Penn P70AA-119, J0019, range 50/300 psig, opens low) fails after six months of service, causing condenser pump to run continuously. Condenser is subject to adverse ambient conditions (freezing temp/high relative humidity) which causes 1) ice to deposit on fan blades (tripping fan vsd on overload) and 2) ammonia migration from hp receiver to condenser (where liquid accumulates in the tubes and restricts hot gas flow, resulting in high back pressure at compressors) and 3) ammonia migration from chiller to high pressure receiver (resulting in low suction pressure at the compressors). Condenser safety valve appears to lift prematurely (less than 250 psi) and does not reseat. Operator error due to lack of training and knowledge also contributed.
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