Workplace Safety North (2015) reported 945 injuries related to mining in 2014 in Ontario, requiring the deployment of 53 emergency response teams. These statistics demonstrate the high risks of serious injury and fatality in the mining industry. Frequently occurring accidents include:​ underground fires, falls-of-ground, mobile equipment collisions, exposure to harmful environments, and falls from heights, which often require rescue (Government of Ontario, 2015b;​ Handbook of Training in Mine Rescue and Recovery Operations, 2014, Workplace Safety North Injury Statistics, 2015;​ Stewart, McDonald, Hunt, & Parker, 2008). Therefore, Mine operators rely on mine rescue teams, who have specialized skills in these issues, to save lives during an underground emergency.

Mine Rescuers regularly participate in training simulations, which require teams of five to seven members, to solve a hypothetical rescue problem while timed and observed by judges (Handbook of Training in Mine Rescue and Recovery Operations, 2014). Simulations typically involve trapped miners who have to be found and rescued under challenging circumstances (T. Hanley, personal communication, December 15, 2017). Mine rescuers carry heavy gear (approximately 100lbs), including a metal stretcher, spare breathing apparatus, hydraulic equipment, and first aid supplies;​ while wearing personal protective equipment (e.g. Self-contained breathing apparatus (SCBA), gloves, helmet, coveralls, boots etc.) (Handbook of Training in Mine Rescue and Recovery Operations, 2014). Research studying mine rescue participants demonstrate metabolic workloads between 400-700 Watts, with short bouts exceeding 1000 Watts;​ and often have concurrent heart rates nearing 100% of estimated maximum heart rate (HR_{max estimated}) (Stewart et al., 2008;​ Tomaskova, Jirak, Lvoncik, Buzga, Zavadilova, & Trlicova, 2015). In addition to extreme physical demands, underground mine conditions are often characterized by temperatures exceeding 40 °C, as well as humidity exceeding 60%, which can exacerbate physiological loads on the mine rescue worker (Kenny, Vierula, Maté, Beaulieu, Hardcastle, & Reardon, 2012). However, research examining the physical demands;​ energy expenditure, physical activity levels, and recovery time associated with event specific mine rescue tasks are limited. Such that current literature does not identify differences between positions, and records data primarily during circuit-type tasks, which allow for more than adequate rest (unlike real conditions).

The present study documented heart rate (HR), respiration rate (RR), energy expenditure (EE), oxygen consumption (V̇O₂), core temperature (T_c), and skin temperature (T_skin) of mine rescuers to produce descriptive statistics and determine vulnerability to heat illness’ (heat exhaustion, crams, syncope, and stroke) during a simulated rescue emergency. The simulation closely mimicked a real emergency because:​ rest was limited, participants lacked information about the tasks, and the rescue was performed in an operational, underground mine;​ which provided realistic physiological responses. Physiological responses were documented with a heart-rate-variability (HRV), body-worn monitor, and a T_c ingestible capsule on each team member, which included a Captain, Vice-Captain, #2person, #3person, and #4person. They performed the following tasks:​ locating and performing first aid to an unconscious casualty (task 1);​ building a barricade to extinguish a fire (task 2);​ provide advanced first aid to a conscious casualty (task 3);​ and carry the casualty up a steep ramp out of the mine (task 4).

The present work highlights the physiological differences between mine rescue tasks and members of a mine rescue team. Laborious tasks were more strenuous than casualty care, however all tasks required a vigorous effort as mean HR of the entire sample exceeded 70% of the age predicted maximum heart rate (%APMHR). Captains exhibited a lower physiological load in comparison to Vice-Captains, #2persons, #3persons, and #4persons during the simulated emergency scenario. Captains also elicited lower T_c compared to other team members. Heat strain was evidenced via an increase in mean T_c to 38.6°C;​ 14 participants (non-Captain) registered a T_c above 39°C.

This research is expected to lead to an improved understanding of the physiological challenges faced by Mine Rescuers. These physiological measures affect worker fatigue and risk of heat stress, both of which increase the risk of injury, and are therefore essential to understand in the development of prevention strategies.