The Science of Hydration: Risk factors for heat related incidents. Insights from the US Mine Safety and Health Administration

September 18, 2023
The Science of Hydration: Risk factors for heat related incidents. Insights from the US Mine Safety and Health Administration

Mining operators in the US are required to report all accidents, injuries and illnesses to the Mine Safety and Health Administration (MSHA). These reports must follow a specific template (MSHA Form 7000-1) detailing the nature of the incident, when and where it took place, the employee’s experience, and the long-term effects of the incident. Each year, thousands of incidents are reported through this mechanism and made publicly available by the MSHA.

Two research groups1,2 have recently published analyses of the MSHA dataset to clarify the risk factors that influence the likelihood of heat related injuries.

Key insight 1 – The majority of heat related injuries occur during summer – but risk is still elevated in spring and autumn

Not unexpectedly, 3 out 4 heat related injuries occurred in the summertime when ambient temperature is highest. However, as 25% of heat related injuries occur in spring and autumn it is still important to take extra care when working in hot and humid conditions outside of the summer months.  If we look at the number of incidents per calendar month, we can see that risk is elevated between May and September, and greatest in July, with very few events reported during winter.


Key insight 2– 60% heat related injuries are reported for workers with less than 5 years of experience.

Worker experience may be a key factor in the heat related injury risk, with 27% of injuries affecting workers with less than 1 year of experience and almost 60% of injuries occurring to workers with less than 5 years of experience. Employees with over 20 years of experience represent  only 11% of all reported heat related injuries.

These number are difficult to contextualise without additional data (most workers may have less than 5 years of experience and/or more experience workers may be performing lower intensity tasks with reduced heat exposure) however these finding highlight the importance of training and educating new employees about the risks associated with heat exposure.  

Additional insights from the MSHA datasets

  • Within each day the risk of injury is highest in the late morning (10:00 AM) and mid-afternoon (4:00 PM)

  • 40% of heat related injuries result in at least 1 day of work lost. 20% of injuries result in 2 or more days of work lost.
  • Heat related injuries can be due to a wide range of factors (environment, lack of acclimatization, heat from activities) and are observed during many different activities (handling, machine maintenance, plant operation).
  • The number of heat related accidents reported each year has not decreased over the last 20 years – indicating the need for advances in heat stress controls.


The MSHA reporting datasets are an important source of information to direct practice and policy, helping us understand how, why, and when heat-related mining accidents occur. Training and educating less experience workers, and increased emphasis on heat stress controls between mid-spring and mid-autumn may help reduce the risk of injury.


1          Lazaro, P. & Momayez, M. Heat stress in hot underground mines: a brief literature review. Mining, Metallurgy & Exploration 38, 497-508 (2021).

2          Talebi, E., Roghanchi, P. & Abbasi, B. in 17th North American mine ventilation symposium, Madiseh A, Sasmito A, Hassani F, Stachulak J, eds. Montreal, QC, Canada.


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