Underground » Health and Safety
The project involved the testing of three diesel engines currently used in underground personnel transport vehicles under a variety of atmospheric conditions which are representative of some but not all underground atmospheric conditions following a mine emergency event. Other equipment identified in the initial study was also assessed.
Initial project objectives were modified following a funding review. The project scope was finally defined as:
- Test three representative engines, namely a PJB Kia Perkins model 6/247, an ABYE Toyota 1HZ and an SMV Perkins, to determine their performance in atmospheric conditions representative of post-incident atmospheres within coal mines. The majority of the testing would be conducted at Simtars on the CSIRO dynamometer with validation checking in normal air and at 3 to 4% natural gas (methane) dependant upon the system capability at Testsafe. A supplementary test was to be conducted to determine what effects carbon dioxide has on the cooling of engine radiators.
- Evaluate the performance of the Miniguide, (Vision assistance instrument used by blind personnel) and assess it for modification to an I.S. unit.
- Evaluation of rapid gas analysis systems
- Evaluation of alternatives for the current alternators fitted to mine vehicles.
The testing identified that all of the diesel engines responded to changes in the gas composition of the atmosphere in a similar manner and are very sensitive to the oxygen percentage when approaching 17% oxygen with 20% carbon dioxide/ balance nitrogen and 15 % oxygen with balance nitrogen.
The impact on the torque and power characteristics of operating a diesel engine under adverse atmospheric conditions was that the peak torque and power decreased with decreasing oxygen levels and increased with increasing methane, to the limits of the tests There was a rapid and significant degradation in performance once the oxygen concentration fell below about 16% and it is unlikely that the engine would produce useful power below this level irrespective of the methane concentration. The ability of any vehicle to climb a grade is determined by the peak torque. The speed of the vehicle would be determined by the engine speed at which peak torque is produced. For all of the engines tested, provided the oxygen concentration was greater than 16 to 17%, the peak torque would usually exceed 80% of that achieved in air and thus it was concluded the engine would perform adequate useful work such that the vehicle could be driven out of a mine.
The limits of testing are summarised in the table below.
| Limit of useable torque | Limit of testing | Limit of useable torque |
Engine
| In reduced O2
in N2 | In reduced O2
in CO2 | In CH4 | In CH4 with reduced
O2 in CO2 |
| No 1 | 15% | 16.5% | 4.2% | 2.3 % CH4 16% O2 |
| No 2 | 15% | 17.3% | 3.3% | 4.7 % CH4 17% O2 |
| No 3 | 14.5% | 16.8% | 4.0% | 4 % CH4 16.5% O2 |
The Miniguide was trialled successfully for a person walking in zero lighting conditions however it was identified as having limited use for the purpose of self rescue whilst driving. A complete redesign would most likely be necessary if the unit was required to be Intrinsically Safe. Some of the limitations could possibly be addressed at this time.
A rapid acting Methane Detector and Monitor was purchased and investigated for suitability for use on a self-rescue vehicle. The instrument represents a significant improvement in response times available for similar equipment currently available.
The project identified a number of Certified flameproof alternators that would be suitable for powering the Methane Detector.
Recommendations - Discussions to be held with legislative authorities with respect to the relaxation of the limits of operation of diesel engines in emergency situations.
- The stakeholder groups (mine workers, owners & Government) all need to consider the results of this research to determine if the current regulations represent the best balance of risk and reward under all circumstances.
- Subject to the recommendation above, AS3584 should be upgraded to allow manufacturers to further test engines that might be required to be used in abnormal atmospheres.
- There is a further need to investigate an engine performance in and through the methane lower explosive limit.
- Further testing using N2O as a low O2 supplement may increase the operating envelope of the vehicles and could assist for starting in low O2.
- The next phase of the project, which involves the modification of an appropriate underground man transport vehicle, should proceed subject to suitable funding arrangements.