Calibration
Avoiding danger in the air
Gas detectors and calibration gas mixtures keep miners safe around the world. Stephen B. Harrison, sbh4 consulting, describes how improvements in technology is saving lives
I
t is a sad fact that underground mining is one of the more dangerous civilian professions that has existed since the onset of industrialisation. However, the good news is that great strides are being taken to improve the safety of miners all around the world. For example: according to data published be the United Stated Department of Labour, the number of mining fatalities in the US coal industry in the decade of the 1990s was 32 per 100, 000 miners; in the first decade of this millennium it fell to 27 fatalities and for the seven full years of this decade the average has reduced to 17 fatalities per year per 100,000 miners. So, what is behind this tremendous increase
in mining safety? Firstly, we must consider the main causes of mining fatalities and they are twofold: problems with the air quality in the mine caused by excessive heat, toxic gases, a lack of oxygen or a build up of flammable gases; secondly incidents related to the use of explosives for rock blasting or collapses caused by drilling. With regard to air quality, there are two main preventative measures that have made a positive impact on mining safety. They are improvements in the ventilation systems that bring fresh air into the mine and the increased use of highly reliable gas detectors that miners use when working underground. In 2015, we saw the closure of the last
underground mining operations in the UK at Kellingley colliery in North Yorkshire. We must therefore turn our attention abroad to
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understand current practices in this industry. So, to examine the topic of ventilation in underground mining, let us consult Barbara Corrêa Avelar, a mining engineer who studied in both Canada and Brazil and has experience at Prospec Jr mining consultancy and Brio Gold Inc at the Pilar mine in Goiás. She says that “specifically, here in Brazil, with regard to ventilation in underground mining, air moving equipment is required to continuously renew the air and thereby provide the right amount of oxygen and to dilute flammable gases and dust. In working areas, the oxygen in the air must not be lower than 19 per cent in volume. In coal mines the air flow must be at least 6m³/min/person, while in other metalliferous mines the air flow must be more than 2m³/min/person.”
GaS detection in tHe mine In the mining industry oxygen deficiency and
CO2 build up are common. Additional hazards also exist, for example Methane is released from gas pockets that are intersected during excavation and can build up to explosive levels. If there is a source of ignition present the ensuing explosion can cause untold damage to
the mine, often resulting in fatalities. H2S is created in the mine due to the breakdown of acid mine water. In some regions of the world it is released directly from freshly exposed coal
faces. So, we can conclude that methane, CO2 and H2S gas detection in the mine would be essential to save lives.
Oxygen levels fall in the enclosed mine
environment because underground machinery and explosives consume oxygen in combustion processes. Only a small reduction from the standard level of 20.9 per cent oxygen in air is regarded as “oxygen deficient” and hazardous. Oxygen deficiency is one of the most notorious and invisible of all mining hazards. In addition, carbon monoxide (CO) is a by- product of internal combustion engines used in mines and of explosives detonations. These by- product gases from internal combustion engines, or explosions, containing CO are often referred to by miners as afterdamp.
KeepinG portaBle GaS detectorS ServiceaBle on a daily BaSiS Coming back to Barbara Avelar, “Different gases can be tested in a mining environment,
usually CO, CO2 and methane, are the most common. Additionally, the gases NOx (The combined quantity of nitric oxide and nitrogen
dioxide), NH3 (ammonia), H2S and SO2 (sulfur dioxide) are commonly associated with metallic ores in underground mines.” What this adds up to is a requirement for a sophisticated range of gas detection sensors to be used in fixed or portable gas detection equipment in mining operations. And, to ensure that the equipment remains functional in the harsh, dusty and damp underground atmosphere, regular testing of the gas detectors is required to ensure the safety of mine workers.
Continued on page 32... September 2018 Instrumentation Monthly
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