Excerpts from article published by Michigan State University Extension.
"When going out on the ice for the first time, only do so after a hard freeze that forms clear solid ice. Four inches of this type of ice will support a person on foot, but it will take approximately six inches of ice to support someone on a snowmobile or ATV. As the winter progresses and the ice thickens, small cars and pickups may be driven out on the ice when the ice thickness reaches 8 to 12 inches. For taking larger vehicles out on the ice, you should wait until the ice cover is well over a foot thick.
Other conditions can also affect the safety of the ice cover. These include inflowing rivers or streams that can delay ice formation along the shore areas where this warmer inflowing water enters the lake. These are dangerous areas that should be avoided. In addition, there are inflowing springs in many lakes where warmer water flows in and can weaken the ice.
For safety purposes, anyone venturing out on the ice should always carry ice picks that can be used to pull yourself out of the water in case you fall through the ice. These can be made by using 4- to 5-inch-long wooden doweling pins of about an inch in diameter. Drive a heavy-duty hardened nail into one end of the doweling pin so that its point projects out the other end. The nail points sticking out of the doweling pins should be sharpened to help penetrate the ice easily. By using wooden doweling pins, they will float in the water in case you happen to lose them from your hands in the water. It is also a good idea to drill a small hole through the doweling pins at the opposite end from where the nail points project and attach several feet of strong cord.
If you fall through the ice, you can dig the points of the ice pick into the surrounding ice while kicking vigorously and pulling yourself out of the water by sliding forward. Once out on the surface of the ice, you should not stand up; but roll away to distribute your weight evenly until you are away from the entry hole.
If you happen to be in a situation where you have fallen through the ice, try to get out as soon as possible because cold water conditions can cause acute hypothermia. The longer a person is in the water, the sooner the loss of coordination and manual dexterity can occur. Cold water conducts heat away from the body 25 times faster than air. Once out of the water, seek shelter immediately."
Hypothermia occurs when the body loses heat to the environment and the core temperature drops below 36.5 C or 97.7F. The rate of heat loss depends on factors such as body morphology, the water temperature, and the body action in the water. As the body temperature cools a loss of strength occurs which will impair the ability to swim. The body temperature continues to drop to the temperature of the water and the person becomes unconscious.
Some complications of hypothermia include: