Defining Cold Water
Rationale For Using 70F (21C) To Define Cold Water
While there is no common or universally accepted definition of cold water, the way that we define cold water, particularly for recreational boating purposes, has important safety implications. The same is true for any recommendations as to when paddlers and small craft operators should consider wearing thermal protection.
In 1983, the US Coast Guard formally defined cold water as anything below 60F (15C), but as the result of a 1998 Congressional inquiry, they subsequently raised it to 70F (21C). The American Canoe Association (ACA) sets their thermal protection threshold at 60F (15C), and another paddling organization, American Whitewater (AW) recommends 50F (10C).
The National Center for Cold Water Safety advises that people treat any water below 70F (21C) with caution. That's also the point at which we recommend thermal protection like wetsuits or drysuits. There's a very sound, science-based rationale for our choice of 70F (21C), and particularly why it differs from 60F(15C) and 50F (10C).
First, we know from scientific research that human respiration begins to be adversely affected at water temperatures below 77F (25C), which is why the International Olympic Committee mandates pool temperatures for competition between 77F – 82F. (25C – 27.7C) Our recommendation of 70F (21C) is six degrees below the point at which respiratory control begins to decline.
Second, research also demonstrates that for unacclimated people, the life-threatening symptoms of cold shock reach maximum intensity between 50F-60F. Since few people are acclimated to cold water, we feel that it's prudent to set the guidelines for thermal protection at a point that's well above the maximum-intensity cold shock range.
Paddlers have a tendency to cut corners when it comes to thermal protection guidelines. For example, paddling groups frequently go out on 58F (14.4) water without thermal protection while citing the fact that it's only 2F (1.1C) below ACA's 60F “cutoff”.
As safety advocates, we think it's prudent to recognize this tendency and err on the side of caution regarding the temperature at which we recommend thermal protection.
An excellent publication with references embedded in the text is Survival In Cold Waters (2003 / 2007), which was authored by Dr. Chris Brooks and published by Transport Canada. On pp16, in the section on cold shock, Dr. Brooks notes the following with respect to water temperature:
“...it is now known that the cold shock response begins at water temperatures below 25ºC (Reference 90) and peak at a temperature between 10-15ºC (References 154 and 155)”.
90. Keatinge, W.R. and Nadel, J.A. Immediate Respiratory Response to Sudden Cooling of the Skin. J. Appl. Physiol. 20:65-69, 1965.
154. Tipton, M.J., Stubbs, D.A, Elliott, D.H. Human Initial Responses to Immersion in Cold Water at Three Temperatures and after Hyperventilation. J. Appl. Physiol. 70(1):317-322, 1991.
155. Tipton, M.J. The Relationship Between Maximum Breath Hold Time in Air and the Ventilating Responses to Immersion in Cold Water. Eur. J. Appl. Physiol. 1992: 64: 426 – 429.