There are three critical phases of cold water immersion. A simple way to remember them is 1 – 10 – 1.
An initial deep and sudden ‘Gasp’ followed by hyperventilation that can be as much as 600-1000% greater than normal breathing. You must keep your airway clear or run the risk of drowning. Cold Shock will pass in about 1 minute. During that time concentrate on avoiding panic and getting control of your breathing. Wearing a lifejacket during this phase is critically important to keep you afloat and breathing.
Over approximately the next 10 minutes you will lose the effective use of your fingers, arms and legs for any meaningful movement. Concentrate on self rescue initially, and if that isn’t possible, prepare to have a way to keep your airway clear to wait for rescue. Swim failure will occur within these critical minutes and if you are in the water without a lifejacket, drowning will likely occur.
Even in ice water it could take approximately 1 hour before becoming unconscious due to Hypothermia. If you understand the aspects of hypothermia, techniques of how to delay it, self rescue and calling for help, your chances of survival and rescue will be dramatically increased.
Prevention and Rescue
The best-case scenario for Cold Water Immersion is to "reduce or prevent the risk". If you're boating early in the season or later in the season when the water is still cold, it's as simple as making sure not to overload your boat, avoiding situations where you may fall overboard and, of course, making sure that everyone is wearing a Coast Guard approved lifejacket to protect in the case of an unforeseeable emergency.
Without thermal protection you can lose body heat 25 times faster in water than in air with similar temperatures and that can be increased by a factor of up to 10 with movement like swimming or moving water.
The best choice in flotation equipment for Cold Water Immersion is a type that will offer the maximum thermal protection such as a floater jacket and pants or a one-piece survival suit. If you do find yourself in cold water, in addition to having proper flotation, there are some things you can do to delay the onset of Hypothermia. Drawing your legs up close to your chest and wrapping your arms around them in a tuck position will help conserve body heat. If you're in a group, huddling together as close as possible will also help conserve body heat.