The estimated annual probability of failure for each explosion protection diesel engine systems (ExDES) item was 23%, it said, which was not deemed to be acceptable.

“Mechanical ExDES failure rates are unacceptable in view of contemporary engineering standards,” it said.

“Like Ex electrical equipment, explosion protected characteristics of an ExDES must have a very low probability of failure. There have been several mine explosions in history where a diesel engine may have been the source of ignition. The consequence of such a failure is potentially multiple fatalities.

“There is a need to continue improving the reliability of explosion protection characteristics of diesel engines systems.”

The inspectorate has called on designers and manufacturers to review the incidents that relate to their ExDES and provide design solutions and critically review and analyse the safety integrity of their shutdown systems and other components. Manufacturers should also use electronic systems where reasonably practicable and review and revise lifecycle inspection.

Personnel with management or control of ExDESs should comply with OEM lifecycle recommendations in their maintenance management system and review maintenance management systems against AS/NZS 3584.3:2012, the inspectorate says.

Personnel should also use the relevant national competencies for the assessment of people maintaining and overhauling ExDES.

The Department of Trade and Investment would implement strategies to improve the reliability of ExDES, including improve the quality of data gathered by introducing an ancillary report form for all ExDES reported (56)(1)(m) incidents and continue with the recognised service facility program for the overhaul of ExDESs.

It would also phase out all older ‘approved’ ExDES currently operating under exemption, by the end of 2013 and publish an update of statistics on an annual basis.

It also intends to implement a program to improve the quality of the design, manufacture and supply of new ExDES consistent with the electrical Ex certification schemes (certificate of conformity) by 2016.

“There has been an improvement in the reliability of ExDES’s over the last 2 years,” it said. “During 2009 there were 345 reported incidents, in 2010 there were 269 and during 2011 there were 230 reported incidents. This is encouraging – assuming the proportion of reported incidents to actual incidents has not decreased.”