As part of a discussion paper unveiled at the Queensland Mining Industry Health and Safety Conference held during August last year, Simtars Occupational Hygiene, Environment and Chemistry Centre manager Darren Brady and analytical chemist Daniel Usher revealed the findings from a gas sample analysis test handed out to seven unnamed underground minesites.
All sites used the gas chromatography based Computer Assisted Mine Gas Analysis System (Camgas) and were asked by Simtars to analyse the test sample containing 2.93% hydrogen, 3.54% carbon monoxide and 11.9% carbon dioxide in a mixture of nitrogen, using their standard method and their mine fire method.
While Camgas instruments have a preconfigured mine fire method calibrated and tested by Simtars on a regular basis, Simtars recommends sites using Camgas to acquire their own fire span gas for calibration containing 3% hydrogen, 3% carbon monoxide and 12% carbon dioxide in a balance of nitrogen.
This allows site workers to maintain the mine fire method calibration on a regular basis and build familiarity with using the method.
However, Simtars in its paper said not all sites had access to a fire span gas and were requested to calibrate with the gases they had available.
The Camgas operators at these sites had to run the test sample without calibrating the fire span points under Simtars supervision.
“This is the situation these sites would find themselves in during an actual emergency until the Simtars cylinder arrived onsite, but with remote, expert support provided by Simtars which is always available around the clock,” Simtars said.
From the testing Simtars observed the gas chromatography instruments of the quad series (1997-2004) could not quantify all components of the test sample when run under the standard methods, due to the detector settings used for routine analysis.
However, all sites successfully analysed the sample on the mine fire method in which the detector settings are suitably configured for the anticipated range.
Using the mine fire method for these instruments was recommended; however, Simtars said the 3000 series (2004-present) did not have the same problems because of a new detector with a wide dynamic range allowing analysis on both the standard and fire methods.
While saying all the testing results were acceptable – despite their variations – Simtars said the success of sites that did not calibrate the mine fire method of analysis with a mine fire span gas on the day relied on a previous calibration.
“This success is based on the instrument response remaining relatively unchanged between the calibration point and the running of any samples,” Simtars said.
“This can never be guaranteed and is why this approach should only be adopted under the supervision of Simtars gas chemists. It is preferential for all sites to have immediate access to mine fire spans for calibration.”
Simtars noted that during a mine fire or advanced spontaneous combustion event it was not uncommon for accelerated levels of hydrogen, carbon monoxide, ethane and ethylene to be produced and the abnormally high levels of these gases in these circumstances mean the majority of mine workers will have no experience in analysing or interpreting the resulting gas chromatography samples.