Thermal status of wet-suited divers using closed circuit O₂ apparatus in sea water of 17-18.5°C

A wet suit may not provide adequate thermal protection when diving in moderately cold water (17-18°C), and any resultant mild hypothermia may impair performance during prolonged diving. We studied heat exchange during a dive to a depth of 5 m in sea water (17-18.5°C) in divers wearing a full wet suit and using closed-circuit oxygen breathing apparatus. Eight fin swimmers dived for 3.1 h and six underwater scooter (UWS) divers propelled themselves through the water for 3.7 h. The measurements taken throughout the dive were the oxygen pressure in the cylinder and skin and rectal temperatures (T(re)). Each subject also completed a cold score questionnaire. The T(re) decreased continuously in all subjects. Oxygen consumption in the fin divers (1.40 1.min^-1) was higher than that of the UWS divers (1.05 1.min^-1) The mean total insulation was 0.087°C.m².W^-1 in both groups. Mean body insulation was 37% of the total insulation (suit insulation was 63%). The reduction in T(re) over the 1st hour was related to subcutaneous fat thickness. There was a correlation between cold score and T(re) at the end of 1 h, but not after that. A full wet suit does not appear to provide adequate thermal protection when diving in moderately cold water.