Perth truck blast probe recommends temporary HC refrigerant ban

reportAN INDEPENDENT investigation into the April 28 Perth truck explosion that severely injured two occupants when hydrocarbon refrigerant ignited upon entering the cabin, has recommended the temporary banning of flammable refrigerants in retrofits and new installations.

“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 into place,” concludes the document’s introduction.

The 123 page report, prepared by WA Government gas regulator EnergySafety on behalf of Worksafe WA, proposes that the ban remains in force until satisfactory engineering standards are established and suitable components become available for retrofits and new installations in mobile and stationary equipment.

Although EnergySafety does not regulate the WA refrigeration and air conditioning industry, it has extensive experience in the behaviour of hydrocarbons, hazardous areas and has the resources to conduct such an investigation.

The investigation centred on an automotive incident but the report also extends the proposed flammables ban to stationary equipment – with the exception of refrigerators purpose-built for these gases – as the investigators believe fixed installations “suffer from the same, if not worse, safety issues when ill-conceived conversions are carried out”.

On more than one occasion the report derides the current situation surrounding hydrocarbon refrigerants in most of Australia as “a regulatory vacuum”.

“At present there is a regulatory vacuum that prevents direct action against anyone using HC [refrigerant] in particularly in conversions in the State of Western Australia and most other jurisdictions in Australia, excepting of Queensland,” reads the recommendations section of the report.

“The overriding feature is that they [hydrocarbon refrigerants] cause danger to the public and workers. Now that this has been established it should be sufficient to put a temporary halt to these activities.”

Throughout the report is the implication that hydrocarbon refrigerants entered the Australian market before industry had time to gain a proper understanding of the issues and potential consequences, which would have led to more thorough engineering practices and solutions and with them a reduction of risk.

An introductory paragraph reads: “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 the flammability issues. Also failure to manage pressure excursions has had major, negative effects that increase the risk of harm to people in vehicle cabins, homes, offices, shopping centres, public spaces and work places.”

In addition to a lack of adequate engineering, the report highlights 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”.

For example, the investigators found the hose connecting the truck’s filter drier and TX valve inlet was “in very poor condition and also suffered from a loss of plasticisers most likely not due to the solvent action of the refrigerant normally used, but more so from the propane/isobutane mixture used as refrigerant since the conversion took place”.

“Although liquid LPG fuel hoses that are compliant with AS/NZS1869:2012 do not suffer from the solvent action from liquid autogas (similar to hydrocarbon refrigerant) they cannot be used as air-conditioning hoses as they would be incorrectly labelled and have burst pressures that are probably lower than required in AC applications.”

The report includes an email from Sanden, which manufactured the compressor used on the truck, saying the company “does not recommend the use of HC refrigerants or alternate oils in our current range of Sanden R134a compressors … Sanden Corporation does not carry a range of compressors specifically designed to use a HC refrigerant”.

There is also criticism the marketing messages of those selling or promoting hydrocarbon refrigerants “in which their flammability is more aimed at warning the installer,” and the “significantly inferior” technical publications used to “justify their products and methodologies”.

Hydrocarbons have not been singled out by the investigators, who also raise concerns over “synthetic flammables” like HFO-1234yf, which is being widely adopted overseas by the automotive sector, as they believe “these refrigerants too require a similar engineering rigour”.

The report recommends that engineering processes, skill sets and working practices found in the petrochemical industry must be adopted by the air conditioning and refrigerant industries if they are to safely work with flammable refrigerants.

It describes this industry as “in the business of handling compressed gases and engineering processes (that involve compressing of gas, highly flammable materials flowing through pipes, hoses, compressors and heat exchangers).”

“In petrochemical process plants professionally qualified personnel are employed specialising in:

  • Pressure containment to determine pipe wall thicknesses and pressure ratings,
  • Process engineering relevant to process safety, plant sizing and,
  • Hazardous Areas specialist from electrical disciplines dealing with management and elimination of ignition sources.”

Rather than suggesting that each automotive conversion should be subjected to the above level of scrutiny, the report recommends that categories and types of conversion should be determined, with each of those checked by a panel of flammables experts before creating “a set of mandatory steps that provides guidance to the installer for each of these categories”.

The report also recommends an “engineering task force” be established to “provide retrofit engineered solutions and ensure supplies of relevant equipment such as compressors, switches, hoses, heat exchangers [and] pumps become available”.

It says the task force should “carry out a number of pilot installations, formulate training packages and roll out training. All this work should be done prior to rolling out any retrofits which are different to the original refrigerant.”

Another task force providing engineering standards for possible inclusion into Australian Design Rules for new vehicles is also recommended for direct installations of air conditioning systems that use flammable refrigerants, ensuring manufacturers stick to “pressure containment and process safety standards”.

Although the investigators acknowledge the fact Singapore and the USA are moving towards banning hydrocarbon refrigerants for applications other than small refrigerators, they believe there is a place for flammable refrigerants to be safely applied in the market provided the correct engineering is applied.

In the report are engineering recommendations for new systems using flammable refrigerants and for retrofitting existing systems with flammable refrigerant. The investigators deem direct systems as impractical for retrofits.

For new systems the report recommends:

  • a high pressure cut-off switch set at 3000kPa
  • a pressure relief valve set at 4000kPa
  • all equipment inside the cabin, compressor discharge and condensing evaporator circuits
  • (including the TX valve) require a pressure rating of 12-14MPa
  • the TX valve positioned outside the cabin
  • no mechanical connections inside the cabin
  • pipework inside the cabin is only subjected to pressure stress
  • a set of solenoids just outside the firewall to keep the bulk of refrigerant outside the cabin when the system is not in use
  • hydrocarbon-compatible liquid hoses

Retrofits are recommended to have the same features as new systems but instead of the solenoid valves would be the the creation of a dual-circuit system by adding a heat exchanger outside the cabin that is controlled by the TX valve, with the other (cabin) side using a set of hoses and tubes to transfer a glycol solution to the existing evaporator inside the cabin, while a small inline pump operates when the air-conditioning compressor cycles on.

The investigators estimate the extra components required for a hydrocarbon retrofit of this type to cost around $550.

READ MORE: Perth truck HC explosion: how it happened

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