Accidental hypothermia occurs very rarely. Japan experienced hypothermic victims in the 2011 earthquake and tsunami disaster. In northern Japan, where the largest class of earthquakes and tsunamis are estimated, study for countermeasures has been advanced. The progression of hypothermia varies significantly by individual differences and environmental factors, and it is considered to be challenging to assess its damage. We present the findings that can be the basis for damage estimation from the data of hypothermia victims experienced in mountain rescue.

From 2002 to 2020, we examined ten fatal cases of hypothermic witnessed respiratory arrest (HWRA) by companions, which led to subsequent cardiac arrest among 164 cases from mountain rescue. We collected the time course of the deceased from rescue records and calculated the time from cold exposure to symptom, exposure to incapable, and exposure to HWRA. Temperature and wind speed data were extrapolated from nearby AMEDAS and upper-air weather records, and the wind chill index (WCI) was calculated.

We obtained the time course data in seven cases of ten, five males and two females between 21 and 67 years old. The weather conditions where the seven cases were placed were -5 to -30°C of WCI. The shortest time from cold exposure to incapacity was 65 minutes, 42.9% (3/7) within 180 minutes, and the fastest time to HWRA was 90 minutes, with 57.1% (4/7) between 10 and 12 and half hours.

For disaster evacuation measures, both evacuees and rescuers need specific indicators to refer to. From very little but valuable data, we consider that rescue within 10 hours is necessary for lifesaving in similar conditions. Additionally, increasing the number of cases that become incapacitated within 1-3 hours can be valuable information for considering the location of the evacuation shelter and evacuation plan.