Cold exposure during helicopter rescue operations in the Western Alps.

Objective: The study evaluates exposure to the cold of personnel involved in helicopter rescue operations in an alpine environment.

Methods: Rescue operations over a period of 15 months in the Oberwallis region (Switzerland) were analysed with special regard to the weather conditions, the locality and its altitude, and the duration. The equivalent chill temperature was estimated with two independent models. "Mean exposure" as well as the "worst-case situation" (based on maximum windspeed) were calculated. The results were evaluated according to the "classic" Siple-Passel model, the more recent model of Danielsson, ISO 11079, ISO 9920, the German industrial standard DIN 33403.5, and the German government regulations for work in cold environments ("G21").

Results: The temperature models showed only marginal differences in chill temperature. Assuming "worst-case conditions", the Siple-Passel model showed that 87.1% of the operations occurred at chill temperatures > -30 degrees C, 12.1% in the range of -30 to -45 degrees C, and 0.8% at <-45 degrees C. The lowest temperature was -54.6 degrees C. The Danielson model resulted in 77.6% without the risk of frostbite, 20.1% with >5% risk, 6% with >50% risk and 1.8% with >95% risk. According to DIN 33403.5, 1.5% of the operations were performed at chill temperatures higher than cold class 1: 2.3% are class 1, 13.3% class 2, 34.7% class 3, 34.6% class 4 and 13.7% class 5. The maximum exposure times of DIN 33404.5 are exceeded in at least 0.5% of the missions. According to ISO 11079, clothing with 2.0 clo is sufficient in 40.2 and 23.9% of the operations [summer, required clothing insulation (IREQ) min. and IREQ neutr., respectively]. In winter the corresponding results are 0.3 and 0.0%. Duration of limited exposure is exceeded in 9.1 (IREQ min.) and 19.8% (IREQ neutr.) of the operations in summer and in 10.3 and 19.8% in winter. According to ISO 9920, ICL min. as well as ICL neutr. is exceeded in 100% in summer and winter operations.

Conclusions: Alpine rescue operations are typical of a place of work in a cold--sometimes extremely cold--environment. Because of the limited time of exposure during the majority of the operations, the most important danger for rescue personnel is frostbite, although hypothermia cannot be excluded in cases of prolonged operations. Special advice to avoid the specific risks must be given to the crews and an examination by occupational medicine, e.g. according to "Working in cold environments, G21" of the German Berufsgenossenschaften, is recommended. Recommendations for adequate clothing are given.