Cold stress is when the body is unable to warm itself up.
Under Health and Safety Regulations ..Employee owes a duty of care .
Continuing to work in Extreme Cold could well be a breach of this duty of care.
OSHA recommends rest breaks to be more frequent and long enough to allow you to properly warm up in a warm dry shelter.
OSHA also recommends no work below 16 degrees.
40 degree temp with wind speed of 35 mph equals 28 degrees so you do your math.
Cold Stress and Cardiac Arrest increase as core Temp. drops below 32 degrees and increases substantially if Temp. is less than 28 degrees.