Preventing Heat Stress in Miners

By Emmanuelle Brière
June 2011

Hard hat, ear protectors, safety glasses, oilers, gloves, rubber boots — protective equipment that restricts cooling through perspiration. Hard hat, ear protectors, safety glasses, oilers, gloves, rubber boots - protective equipment that restricts cooling through perspiration.

Rockslides, toxic gases, dust — these have always been the best-known hazards of mining. But an equally serious hazard to workers’ health and safety is heat stress. Mine temperatures can reach 40°C and significantly affect miners’ health, as well as their productivity. That’s why Natural Resources Canada’s (NRCan’s) CANMET Mining and Mineral Sciences Laboratories (MMSL), in partnership with the University of Ottawa’s School of Human Kinetics, is working with industry for the Deep Mining Research Consortium (DMRC) to find and reduce the particular causes of heat stress in miners. Heat stress mitigation is much more than a health and safety issue, it also causes the mine’s ventilation infrastructure to operate at high levels of capacity and increases the costs associated with refrigeration systems.

What is Heat Stress?

Heat stress occurs when body heat generated by physical effort combines with clothing effects and environmental conditions — air temperature, relative humidity, air movement, heat radiation — to produce a dangerous increase in core body temperature.

Measuring body heat generation in the University of Ottawa's calorimeter lab. Measuring body heat generation in the University of Ottawa’s calorimeter lab.

For miners, these three factors — and with them, a high risk of heat stress — are inherent features of their normal work conditions:

  • First, even though mining is highly mechanized, miners still must expend significant physical effort, which can quickly increase their body temperature.
  • Second, underground environmental conditions are especially intense the deeper down you go. Thus, for every kilometre in depth air has to go underground, its temperature can increase by approximately 10°C due to auto-compression. And this effect is further amplified by humidity, since water is used in various mining processes.
  • Third, miners must wear use special clothing and equipment to protect them from the occupational hazards of cuts, fluids, head impacts and noise.

Each of these conditions, by themselves, is a significant factor for heat stress. When they are combined, as they routinely are in mining, the risk of heat stress is exponentially greater.

Understanding Heat Sources

To reduce the potential for heat stress in miners, the researchers studied the day-to-day work at Agnico-Eagle Mines’LaRonde property in Cadillac, Quebec, and Vale Inco’s Garson Ramp project in Sudbury, Ontario. Physiologists recorded the movements and other physical efforts of miners as they worked and conducted rescue activities.

A wide range of information was collected. “We needed to evaluate the most common mining occupations and intense activities, observing their work practices, what loads were being lifted, whether they’re walking up hill, whether they’re climbing, doing upper body work, leg work, standing, sitting, the duration of these elements, their frequency, rest periods, etc.,” says Stephen Hardcastle, senior research scientist at MMSL. “We then had to determine how much energy the miners were expending and how it increased their core and skin temperatures.”

The self-contained breathing apparatus adds to the weight that a mine rescue crew must carry and increases the energy they use. The self-contained breathing apparatus adds to the weight that a mine rescue crew must carry and increases the energy they use.

Measuring Body Heat

Once the particular activities were classified, they were reproduced by volunteers in the University of Ottawa’s laboratory in order to precisely measure the amounts of body heat that were generated by the activity, lost to the environment and stored in the body. These experiments would not have been possible without the participation of the university, which has the world’s only “gold standard” calorimeter for human studies. Stephen says: “With this tool, we are able to look at how volunteers’ bodies are storing heat and how much oxygen they’re using, which is a measure of how much energy they’re expending doing their various tasks on a second-by-second basis.”

Research Benefits

While this research is still ongoing, it has already been useful in identifying appropriate work clothing for miners. Further important aspects of the study are determining how miners should balance work and rest and designing management strategies that take into account the varying rates at which heat is stored or lost during these activities. Findings in these areas will not only help protect workers but also increase the productivity of the Canadian mining industry.

For further information on heat stress and its prevention, visit the Canadian Centre for Occupational Health and Safety (CCOHS).

To read about related articles, see Mining Safety Measures

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