There are four stages of cold water immersion. This is what happens in the first two stages.
- Stage 1: Initial “cold shock” occurs in the first 3–5 minutes of immersion in cold water. Sudden immersion into cold water can cause immediate, involuntary gasping; hyperventilation; panic; and vertigo—all of which can result in water inhalation and drowning. Immersion in cold water also can cause sudden changes in blood pressure, heart rate, and heart rhythm, which also can result in death.
- Stage 2: Short-term “swim failure” occurs 3–30 minutes following immersion in cold water. The muscles and nerves in the arms and legs cool quickly. Manual dexterity, hand grip strength, and speed of movement all can drop by 60%–80%. Even normally strong persons can lose the strength necessary to pull themselves out of the water or even to keep their head above water. Death occurs by drowning.