A faulty gas-monitoring sensor is believed to have contributed to an incident in which 18 workers were exposed to a potentially deadly gas at a copper and zinc mine near Millertown, Newfoundland.
At about 8:05 pm on January 4, a half-hour into the night shift, employees of the Duck Pond Mine were working 250 metres below surface when one miner reported smelling gas, says Larry Bartlett, human resources superintendent for mine owner, Teck Cominco Ltd.
The workers left the mine and were taken to a nearby hospital as a precautionary measure, Bartlett reports. The workers did not demonstrate any noticeable effects of what was determined to be sulphur dioxide (SO2) gas exposure, and were sent home by 6 am.
Acute exposure to the pungent and irritating gas can cause burning, stinging and watering to the eyes, nose, mouth and other parts of the respiratory tract, says information from the Occupational Health Clinics for Ontario Workers. Higher concentrations can cause more severe irritation, but extremely high concentrations can lead to damage to the respiratory tract or even respiratory paralysis and death, the Ontario clinic reports.
Vanessa Colman-Sadd, a spokesperson for Newfoundland and Labrador’s Department of Government Services, says the SO2 leak occurred following a routine development blast.
When sulphide ore is blasted, Bartlett explains, the dust generated ignites and explodes, producing SO2.
Teck Cominco has determined signals from a fixed underground gas detection unit were not reaching an aboveground monitoring system, he says. The underground unit — containing a protective outer casing and cables inside a sheath — has four pairs of wires to detect SO2, carbon monoxide (CO) and nitrogen dioxide (NO2) gases, as well as carry power to the surface monitoring system.
Initially, Bartlett reports, CO levels were fluctuating on the surface monitor, “which lead us to believe that the particular sensor was working well.”
The problem was that the cable, either before or after that point, “had been squashed by a piece of equipment,” he says. “Unbeknownst to us, the casing wasn’t broken, but the wire inside that’s supposed to deliver the SO2 signal was, so there was no reading coming up on surface.”
At some point, not only were the wires to the SO2 monitor broken, the other monitors were not working either, says Bartlett. That meant readings were not registering on the surface monitor.
Teck Cominco has returned the CO and NO2 sensors to the manufacturer, Bartlett says, noting that they had just been installed in late December.
The company is also planning to install an alarm on the monitoring system that will sound if a reading is not received from any of the three sensors. “We were fortunate that we were able to learn from this event,” Bartlett says.
Many mines, until recently, had their people wearing gas monitors and found that this type of protection was not enough. Many have gone to the wall alarm system, one that was attached to the centre computer system. Any early detection and the wall alarm system would go off and alert the supervision on-site. As a backup plan there would be the portable alarm that would, in all probability, be going off before the central alarm system.
As a last word, the protection of the two alarm system is due to the vigilant calibration process. Ensure that your company has the calibration process in place that is foolproof. In other words, test the system periodically to ensure that the system IS working in a foolproof manner.
Remember — In Ontario, “ALL Accidents are Preventable”
‘Work’ and ‘Play’ safe.
Daniel L. Beal
CHSEP — Foundation Level
VP & Senior Trainer