Some shocking cold

Sean and Dean with different head wear

More than 50% of immersion deaths are caused by cold shock and swimming failure.

Cold shock is exactly as advertised, a shock from sudden immersion in cold water. The surprising thing about cold shock is that it begins at 25 C; its effects peak at 10 - 15 C. If you think back to being a kid, even in summer the water felt cold until you got into it for a while.

Cold shock lasts for 2 - 3 minutes. The first response to cold shock is a sudden, large inspiratory gasp, that is breathing water if you're upside down. That's followed by up to a four-fold increase in breathing rate, best if the head was above water. The blood vessels constrict causing a massive increase in heart rate and blood pressure. If the ingestion of water doesn't kill then less fit individuals could die of cardiac arrest.

Our seawater temperature now is in the 1 - 2 C range so cold shock is a very real concern when kayaking in winter. What can be done to minimize the risk? Primarily, wear head protection such as a neoprene skullcap, dive hood or similar gear. That protects the head from the sudden cold at immersion. I wear a neoprene skullcap and I've started wearing my helmet.

The other helpful thing is to practice cold water immersion. This can be as little as putting the face in cold water to get used to the cold.

On Saturday some of us wore wool hats or the like. These could come off and cause the gasp reflex under water. Just be aware of the risks whatever you wear.