One of the joys of diving — especially during the summer — is leaving behind the heat of the day to descend into cool water. But wearing wetsuits on the surface, exerting yourself and spending time under the sun on a boat or at the local quarry can elevate your body temperature.
Understanding Heat Transfer
To understand how best to prevent and manage overheating on the water or in the field, a basic knowledge of heat transfer is helpful. Heat energy is transferred in four ways: conduction, convection, evaporation and radiation.
In conductive heat transfer, heat energy moves from a warmer object to a cooler object or medium in direct contact with it. A warm body on a cold ground or boat deck is an example of conductive heat transfer in action.
Thermal Challenge: Heat Illness (Hyperthermia)
Consider this scenario: You’re enjoying a wonderful day on a dive boat. As you wait to make your way to the rear of the vessel, you strike up a conversation with another diver in the back of the line. For nearly 15 minutes the two of you stand in the sun in head-to-toe black neoprene. By the time you make it to the stern, the man you’ve been talking to says his stomach doesn’t feel well. You notice that he is sweating, his face is pale, and when he goes to put on his fins, he almost collapses.
Heat exhaustion is the result of a hot environment combined with insufficient hydration. A heat-exhausted person may be insufficiently hydrated due to sweating, breathing dry air, inadequate fluid intake, vomiting, diarrhea and, perhaps most often, a combination of several of these factors. Common symptoms include headache, nausea, dizziness, vomiting, profuse sweating, pale or flushed skin and disorientation.
The primary problem for the heat-exhausted individual is fluid volume depletion, so rehydration is the cornerstone of treatment. In addition to encouraging the person to hydrate, find a place for them to rest in the shade.
As in treating hypothermia, consideration of the mechanisms of heat transfer can be helpful when treating heat illnesses (hyperthermia):
- Conductive heat loss can be encouraged by placing an ice pack or cold compress on a hot person. Clothing should be removed to reduce insulation. Make sure the person is moved off of asphalt or other hot surfaces; if you can find a cool surface on which they can rest, use it.
- Convective heat loss can be promoted by fanning the person.
- Evaporative heat loss is best achieved by keeping the person’s skin moist.
- Radiative heat gain can be minimized by moving the person out of direct sunlight. Radiative heat loss can be promoted by moving a person to a cooler environment if one is available.
Avoid hyperthermia by wearing a hat, drinking plenty of fluid and keeping your skin in the shade as much as possible. Keep tabs on how you feel; if you are uncomfortably hot, take action to cool yourself off.
Unlike heat exhaustion, heat stroke is a true emergency that requires intervention by medical professionals. Heat stroke is the elevation of a person’s core temperature to greater than 105°F (40°C). Factors that can precipitate heat stroke include physical exertion, extremely hot environments, improper clothing and a physiological inability to compensate for increased heat.
Since the brain is particularly sensitive to temperature changes, symptoms of heat stroke are not unlike those associated with a head injury and may include hallucinations, combative behavior, seizures and decreased mental status. The person with these symptoms must be cooled aggressively. In the hospital, they may be immersed in a bath of ice water; but in the field, immersing a person who cannot control their own airway is not recommended. Instead, strip the person, soak them with water, and fan them to maximize the effects of evaporative and convective cooling. In the event that ice or cold packs are available, place these at the person’s neck or armpits. Direct the open valve of a scuba cylinder, if there is one nearby, at the person to increase convective cooling. Even if the person seems to improve significantly, they must be monitored closely until they can be evaluated by a physician.
Preparing for hot, sunny weather is important when spending time outdoors. Proper clothing, adequate food and hydration, and a basic understanding of the mechanisms of heat transfer are essential for both personal safety and the ability to care for others on the water.