After measuring the energy output of miners doing different tasks at Agnico Eagle’s La Ronde Mine, Dr. Glen Kenny and Dr. Francis Reardon used the direct calorimeter to simulate the physical activity.
Core body temperature alone only provides a “one-sided look at what’s going on,” said Kenny, Canada Research Chair in Environmental Physiology. The other side of the equation, heat loss, “can’t be measured in the field because there’s no magic way to do it. What we’re doing here at the University of Ottawa with our direct calorimeter is measuring the body’s capacity for heat dissipation in specific environmental conditions.”
The body dissipates heat by increasing blood flow to the skin and transferring it to the environment – much like the radiator in a car, explained Kenny. The skin surface is then cooled through airflow and the evaporation of sweat.
In the direct calorimeter, Kenny and Reardon can measure how much heat is being dissipated with an accuracy of plus or minus two watts. “That’s pretty amazing when you think about it,” said Kenny. “That’s one-third of the heat energy of a Christmas light bulb.”
Guidelines and thresholds commonly used to indicate a potential risk of heat stress are based for the most part on core body temperature and on studies done on young, healthy males.
“The problem you have is that a lot of the miners are obese and older – the average age of a miner is 42 – so we have an aging workforce, and there are miners with type 2 diabetes. As we get older, we don’t have the same capacity to regulate core temperature. Type 2 diabetes compromises skin blood flow. It affects sweating activity, and if you have any alteration in your ability to dissipate heat, it’s going to compromise your ability to thermoregulate in these difficult environments.”
Clothing is another factor.
“A lot of miners don’t really know what to wear,” said Kenny. “Anytime you’re wearing any kind of a garment, you’re impeding heat dissipation. The best way to dissipate heat is to be nude.”
With the direct calorimeter, Kenny can measure the exact effect that different clothing and materials have on heat dissipation.
“If I have a worker in there, I’ll put him in nude. He’ll exercise for two hours, then we’ll put clothing on him – whatever they want us to evaluate – and we’ll be able to measure precisely how much a particular material or garment impedes heat dissipation.”
Ultimately, the objective of the research is to arrive at guidelines and recommendations tailored to miners and the environment in which they’re working.