>>1871127A few hours or less at 30-40F can kill a person if you're fully naked and exposed the entire time. It can set in within minutes in water that cold as well and kill within hours. If you're covered up properly and have your wits about you though it's usually well below 0F depending on your layering. For example, it's probably possible to survive a night at 32F in just a t-shirt and pants, whereas at 0F it's very likely for you to die dressed like that overnight without a fire.
