Working in extreme cold and hot conditions are both hazardous.
Working in extreme cold can induce hypothermia, a significant drop in body temperature. Hypothermia can lead to death, but usually the most common symptoms are exposed time in cold weather, confusion, shivering, lack of motor skills, and unconciousness.
Working in extreme hot can be dangerous too. This is called hyperthermia, which is the body not being able to regulate body temperature due to cold conditions. Heat stroke can happen, which symptoms include headache, hot temperature, dizziness, and unconciousness.
