Mine rescue volunteers are considered elite miners; the best at performing difficult tasks under difficult conditions underground. But, regardless if they’re volunteers or not, they are no less susceptible to the dangers that all workers face under extreme heat exposure.
In fact, because of the nature of mine rescue work, mine rescuers may be considered at greater danger of heat stress than any other job, certainly within the mining industry.
In Poland in 1998, 10 mine rescuers under oxygen were overcome by heat during an exploration activity and on several subsequent rescue attempts, temperatures peaked only at 31.5°C (88.7°F), but the relative humidity was in the high 95 to 98 per cent range. Six died and one suffered severe injuries.
Several years later, in October 2002, two members under oxygen of a mine rescue team collapsed in the heat while exploring an abandoned mine stope in Nevada. They encountered temperatures exceeding 39.4°C (103°F). One of the members died on site, while the second died a week later in hospital.
In 2011, three mine rescuers died of heat stroke while fighting a coal mine fire in China’s Shandong province, and heat exposure was a factor in the deaths of two South African mine rescuers during an emergency in 2012.
Incidents such as these, and a growing awareness of the issue as Ontario mines encounter hotter mineral formations and reach deeper depths, prompted Ontario Mine Rescue to join others in supporting research by the University of Ottawa into heat exposure and heat stress in mining and mine rescue.
Several significant reports into workload, heat-stress management, and the effect of garments in mine rescue, have been completed and further research is ongoing.
Understanding how the body responds to heat, the dangers posed by heat stress, recognizing the factors that contribute to heat stress, and taking preventive measures should not only safeguard mine rescue volunteers, but also the mine rescue team, and allow the best opportunity for safe and successful missions.
Normal core body temperature is 37°C (98.6°F), though there is slight variation among individuals of about half a °C. This temperature must remain relatively constant for the body to work well. As body temperature rises, the body automatically takes a combination of steps to cool or lose heat to maintain a relatively constant temperature.
Mine emergency and emergency training situations tend to place mine rescue team members at a higher risk of heat stress than ordinary mining activities. Team members can face extreme heat loads not only due to environmental factors that will be less than ideal, but also due to their metabolic work output and clothing.
In a rescue environment, existing engineering controls: fans, ventilation, heat shields and barriers, may have limited effectiveness or no longer work.
Environmental factors may also be subject to new influences: fire and flooding, that pose increased variables and dangers.
Mine rescuers may have already have put in partial or full-work shifts when called to action, contributing to fatigue and dehydration.
The emotional urge and psychological stress to respond quickly to an emergency may inhibit a rescuer’s ability to self-assess his or her personal situation.
During rescue operations, mine rescuers may travel long distances on foot over uneven terrain, wearing breathing apparatus and under oxygen. They usually carry heavy loads, and do extreme physical and often psychologically demanding work. Muscular work can increase the heat production in the body 10 to 20 times that of when at rest.
The breathing apparatus and additional protective clothing worn by mine rescuers can also add to the heat burden by increasing a rescuer’s metabolism, containing the perspiration, and preventing or reducing cooling.
Protective equipment and clothing can also make it difficult for mine rescuers to recognize heat stress symptoms in each other until heat stress reaches a critical level.
Ontario Mine Rescue has a number of sets of the recently developed Dräger hydration masks for use with Dräger BG4s, which may not be available, therefore mine rescuers may have no opportunity during an assignment to drink fluids to rehydrate their bodies. As well, during an assignment, rest conditions are often less than ideal.
Since work in a hot, humid environment will create a higher heat-stress level than the same work in a normal environment, occupational health authorities, industrial hygienists, and researchers in different jurisdictions have developed work level/time exposure guidelines and standards to limit the likelihood of people suffering heat stress disorders while working.
Within Canada, provinces and various agencies have established guidelines and standards to regulate heat exposure in the workplace, including mines.
To fulfil their health and safety responsibility to workers as required under the Occupational Health and Safety Act (OHSA), Ontario mines use a range of measures, principally ventilation, exposure time limits, training and acclimation to hot environments to control heat exposure for workers.
None of these guidelines/standards, however, are directly and easily applicable to the dynamic conditions and situations faced by mine rescuers, but would require relatively complex adjustments, most involving multiple subjective evaluations unique to the emergency situation and specific mine site, to be adapted for use in mine rescue.
In contrast internationally, different countries, several of which have conducted substantial research into heat exposure and heat stress in mine rescue activities, have developed standards and protocols specific to their own legislative requirements, and the occupational health and safety needs of mine rescuers.
A straight comparison of standards among international mine rescue organizations is difficult due to different approaches and methods used in research efforts. Various standards are often expressed using different combinations and formulas of dry bulb and wet bulb temperature, relative humidity and dry bulb, wet bulb globe temperature (WBGT), and other environmental measurements.
As well, some jurisdictions have attempted to target their research and subsequent heat exposure limits or tolerance times to be appropriate for their “standard” of mine rescuers, such as fitness level, age, and heat acclimation, as well as other jurisdiction-specific criteria such as breathing apparatus, cooling vests, protective clothing, and type of mine.
Mine Rescue Services Ltd. (MRSL), which administers mine rescue in the United Kingdom, had a comparison prepared in 2008 by the Institute of Occupational Medicine (IOM), a leader in heat exposure research in mining and mine rescue activities in the U.K. since the 1950s.
Though the comparison revealed a variance in approved safe working durations among the surveyed jurisdictions at relatively lower wet bulb temperatures (25 to 30°C), the variance quickly diminishes in the mid-range and upper range of wet bulb temperatures.
It should be noted that South Africa, which has the longest safe working duration limits for most of the temperature range, has specific age, fitness and acclimation requirements for its mine rescuers.
All personnel involved in mine rescue activities, as well as mine management, should be aware of the risk of heat stress, and take appropriate control and preventive measures to identify, evaluate and reduce the hazards that may lead to an incident of heat stress disorder during all mine rescue activities.
*Meg Parker is writer/editor of WSN’s monthly newslette, Every Worker.