Cardiac risk and hydration

Working on wildland and urban interface fires can involve environmental and physiological extremes beyond which the human body was meant to endure. Our past research showed that firefighters regularly experience sustained and unsafe peak heart rates, maintain dangerously high core body temperatures and rapid respiratory rates, and regularly experience high levels of dehydration, all while being exposed to an atmospheric cocktail of hazardous, toxic, and carcinogenic air and skin pollutants. Not surprising, sudden cardiac death is the leading cause of on-duty fatalities(1).

It is well recognized, that drinking fluids is important to replenish electrolytes and maintain safe hydration levels throughout the day, especially when doing hard work in hot and humid conditions. OSHA encourages workers to drink a liter of water over one hour, which is about one cup every fifteen minutes (2). Additionally, it is well known that drinking water can help reduce cardiovascular stress and mitigate rising core body temperatures. Whether you follow a hydration regimen or practice ad libitum drinking (drinking when thirsty), it’s important to make sure you drink enough water to help avoid heat-related injuries and reduce thermal and cardiac stress.

There is however a distinct advantage to drinking colder water, especially when it comes to your core temperature and heart rate. In our recent research we tracked firefighters across a variety of duties including trainings, controlled burns, fuels reduction, and actual wildfire incidents. Comparisons were made between firefighters who drank iced water (~32 F) to those that drank ambient temperature water (~75 F). Those that drank colder water:

• Were less likely to be dehydrated at the end of the shift
• Were more likely to maintain safer levels of hydration throughout the shift
• Had lower heart rates
• Had lower skin temperatures
• Were able to return to "normal" heart rates and core temperatures faster after hard work
• Were able to maintain more "normal" and "stable" core temperatures and heart rates throughout their shift