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“The LHD in question had been experiencing reliability issues with the low water shutdown protection system,” NSW Department of Primary Industries spokesman Tony Linnane said.
During a fault-finding exercise on an LHD vehicle, three plastic floats located inside the water-based exhaust system were found to be melted from excessive heat.
During a period of a couple of weeks the original equipment manufacturer’s service personnel and mine personnel had attempted to rectify the problems with limited success.
While extensive testing on the circuit components found no failure, the investigation did find that by setting the operating pressures to above that recommended by the OEM, the protection systems would be defeated and render the explosion-protection characteristic non-existent.
Investigations also revealed the ease at which the safety system pressures can be adjusted to unknown values, thus rendering the protection system ineffective.
The machine had been assigned to work in a hazardous zone by contractors, where the mine atmosphere contained varying concentration levels of methane gas in the return airway.
Recommendations include:
A person must not, intentionally or recklessly, interfere with or misuse anything provided in the interests of health, safety and welfare under occupational health and safety legislation.
Designers, manufacturers and owners must ensure that engine shutdown systems comply with AS 3584.2. Diesel Engine Systems for Underground Coal Mines Part 2 Explosion-protected, which in clause 2.14 includes the requirement that the engine shall be fitted with fail-to-safe automatically operated engine (fuel) shutdown.
Designers and manufacturers must ensure that safety shutdown systems are analysed to an appropriate risk-based method to establish if they are fit for purpose. The use of failure modes and effects analysis may be appropriate.
Designers must eliminate the use of single line components on safety critical systems or functions. The system must be designed to the required safety integrity level.
