To Avoid Hypothermia, Divers Should Stay “in the Hood”

Steve Muscat, chief diving medical officer for the government of Malta, says most of the hypothermia problems he sees as a dive doctor are usually a result of thermal cooling of the head. Heat loss from the head in cold water can account for more than half the resting metabolic heat production.

"Dive schools do not usually give head protection to novice divers in warm water for the initial dives, as this gives a greater sense of freedom, reduces claustrophobia and enhances hearing," Muscat wrote in his regular column, "Dive Medic," for Asian Diver magazine. "The reasoning is that there is then a greater chance of their booking a course for more dives. The problem is that dive schools commonly end up losing business because the diver has ear and sinus problems related to exposure."

Even experienced divers can have problems due to badly-fitting or inadequate hoods. Case in point: A very experienced dive instructor did two consecutive dives on the MV Rozi wreck in Malta at 100 feet, with a sea surface temperature of 77 degrees, and 59 degrees at the bottom. He was wearing an 8-mm wetsuit with hood attached. But when starting his safety stop at 15 feet at the end of his second dive, he experienced an earache on the right side, and sudden vertigo. Recognizing the condition, he wisely went back down to 30 feet, where his symptoms subsided, then slowly made his way to the surface, swallowing hard all the time. When he went to Muscat for examination, the diver had typical signs of middle ear barotraumas -- bruising of his eardrum and blood-stained liquid in his middle ear. He had never had any similar symptoms prior, nor a history of common cold or allergy conditions.

Unfortunately, the episode repeated itself less severely with both ears three months later. Muscat recommended using a double hood, a single-lined 1-mm hood under his wetsuit hood, which worked wonders, but he also advised the diver to give up his career as a dive instructor to better protect his ears.

Muscat's advice: Avoid ear issues by always diving wearing a comfortable, well-fitting hood if your dive is going to exceed 20 minutes in water colder than 77 degrees. And doing a long surface interval to let your body regain thermal normality is essential for multiple dives.