The NSW Department of Primary Industries issued a safety bulletin this week on the potential for flameproof headlights to exceed a surface temperature of 150C.
Variation in voltage, angle of inclination of the headlight, the type of lamp used and the ventilation around it can all affect the surface temperature.
DPI said it had also been made aware of headlight failures due to impact and excessive internal heat generation leading to premature failure of internal components and wiring and the possibility of 12 volt-rated lamps being supplied at a voltage of 13.8V.
The requirements for thermal tests on explosion-protected equipment are contained in AS/NZS 60079.0:2005 Electrical apparatus for explosive gas atmospheres Part 0: General requirements, and IEC 60079-0, Ed.4.0 (2004) (Incorporating Amendment No 1) Electrical equipment for explosive gas atmospheres - Part 0: General requirements.
"For electrical apparatus which can normally be used in different positions, the temperature in each position shall be determined and the highest temperature shall be considered. When the temperature is determined for certain positions only, the electrical apparatus shall be marked with the symbol "X" to indicate this special condition of use," according to Section 26.5 on thermal tests.
Section 29.2 states: "If it is necessary to indicate special conditions for safe use, the symbol 'X' shall be placed after the certificate reference. A warning marking may be marked on the apparatus as an alternative to the requirement for the 'X' Marking."
DPI also pointed out the manufacturer should ensure the requirements of the special conditions for safe use are passed to the purchaser.
DPI recommended all coal operations should review any information supplied with the flameproof headlight for compliance with the Occupational Health and Safety Regulation 2001, and to review the obligations to control risk under the Coal Mine Health and Safety Regulation 2006, Clause 4.
It noted the risk from excessive surface temperatures can be eliminated by design and verified by thermal tests with the headlight in the worst-case condition.
Headlights must not be operated at a voltage greater than that specified in the certificate of conformity, or if the voltage is not specified it shouldn't be more than the nominal voltage of the lamp.
Also, only the type of lamp specified must be used. If the type is not stated, operators should use the same model and rating they used during testing for certification.
DPI pointed out that headlights must not be inclined or operated in conditions that may cause it to exceed a surface temperature of 150C.
"Where headlights have not been tested and certified in the 'worst-case' position, inspection and maintenance programs shall include the measurement and recording of surface temperatures of the headlight," DPI said.
"The ambient temperature shall also be recorded. The inspection and maintenance program shall include checks at regular intervals to ensure the headlight is used in accordance with its conditions of certification.
"Where headlights are found not to be used in accordance with the certified conditions, this is considered to be a failure of the explosion protected characteristics as per Clause 56 (1) (m) of the Coal Mine Health and Safety Regulation 2006."
DPI added that, where temperature measurements adjusted for an ambient temperature of 40C exceeded 150C, the headlight must be removed from service.
