By Elvis Hoffpauir, MACS president and chief operating officer
VASA, which represents mobile A/C, electrical and cooling system professionals in Australia and New Zealand, has long sounded warnings about the potential dangers of using hydrocarbons in mobile air conditioning systems not designed for flammable refrigerants.
The organization recently reported the results of an independent investigation into an April 28 truck explosion in Perth that injured two occupants when hydrocarbon refrigerant ignited in the passenger cabin. It was reported that the truck had been retrofitted with hydrocarbon refrigerant as part of a major air conditioning system overhaul.
The investigation was conducted by the Government of Western Australia (WA) gas regulator EnergySafety on behalf of Worksafe WA. VASA cites an excerpt from EnergySafety’s 123-page report which states: “This report firmly recommends a temporary halt to the use of hydrocarbon refrigerants in any conversions fixed and mobile until revised and improved safety measures are put in place.”
An introductory paragraph of the report states that “In general the introduction of HC [refrigerants] has occurred without implementing major improvements or modifications of design philosophies of equipment and plant to deal with flammability issues,” and goes on to highlight the fact that “there are no known suppliers of equipment certified for use with HC refrigerants available from reputable manufacturers of compressors, TX valves, hoses, pressure switches and relief valves.”
According to the report, the driver and passenger of the truck saw “smoke” moments before the blast. Investigators say the “rapid discharge of liquid/saturated [refrigerant] vapor would have looked like a mist/fog or smoke and caused turbulent mixing with the air.”
The truck’s occupants reportedly suffered second- and third-degree burns, and exited the vehicle while it was still in motion. “Once the driver and passenger were outside, others present assisted in putting objects in front of the wheels to prevent the vehicle rolling away,” says the report. “Had the vehicle been travelling at speed the consequences could have been far worse … the driver was dealing with an explosion in his cabin and this could easily have resulted in a collision and further dire consequences.”
VASA reports that “Investigators found the diaphragm of the truck’s TX valve had separated from the main body, a rare occurrence that the manufacturer of the failed valve … told investigators would have required pressure exceeding 4.45MPa.
According to VASA, “investigators found the reason why the system’s pressure got high enough to rupture the valve and cause an explosion – a non-operational condenser fan … Resulting from the lack of suitable pressure switch or relief valve, the truck’s air conditioning compressor was uncontrolled once the condenser fan stopped working and with the runaway build-up of pressure ultimately reached the point where the TX valve became the weakest link and failed.”
“The TX valve’s location behind the truck’s dashboard allowed refrigerant to enter the cabin at high pressure.” The report says, “a propane/air mixture requires just 0.2 millijoules to ignite, less than the spark energy from a person’s fingertips when getting out of a vehicle on a cold day.”
For more of their report, check out the following links on the VASA website: