You’re taught recreational decompression tables and theory during your entry level SCUBA courses and most divers rely heavily on their Personal Dive Computer (PDC) to keep them safe whilst diving but everybody is not the same and it can be dangerous to blindly follow what your dive computer is telling you so you can avoid a visit to one of these. There are many different factors that affect decompression but I’m just going to focus on how your body temperature can affect your decompression profile in this blog.
I don’t think anybody truly enjoys being cold during a dive but being warm during a dive can have adverse effects with your decompression tables. Studies have shown that when you are warm during a dive your metabolism will increase and you will absorb more nitrogen into your tissues. The same increase in metabolism will increase your rate of off-gassing which can lead to decompression sickness (DCS). The study performed by the NEDU used a simple dive profile, repeated 484 times with 73 Navy divers, which consisted of a 30 minute dive time and a decompression stop of 91 minutes but they changed the diver’s temperature at different stages of the dive from ‘warm’ (36°C) to ‘cold’ (27°C). The study found that when divers were warm during descent and cold during ascent and decompression, even with a 91 minute deco stop, that seven out of thirty two subjects or 22% had some kind of decompression sickness. Of the divers with the same dive profile but who were ‘cold’ during descent and ‘warm’ during ascent and decompression; none of the eighty subjects had any decompression sickness. Because of the significant difference in these two thermal profiles warm>cold and cold>warm they changed the profile on the cold>warm to more than double the bottom time to 90 minutes but found that only two out of the one hundred and fifty cases showed signs of decompression sickness so 0.1%. This says that your body temperature has a huge effect on your rate of decompression and unfortunately it is best to be cold for the main part of your dive and warmer whilst decompressing.
‘But my dive computer measures water temperature’ you say, that’s great but there are no dive computers with algorithms that compensate for changes in body temperature. Measuring the water temperature has no reflection on what your body temperature is as you can be wearing any kind of wet suit or dry suit.
I imagine most British divers as soon as they exit the water after a cold dive go and drink a warm cup of tea or coffee, this isn’t a huge issue as your external body temperature will not fluctuate too much. Warming your extremities on a heat source or rushing somewhere warm on the other hand can have an adverse effect on your decompression state. A rapid increase in body temperature in your extremities can cause dissolved Nitrogen in your tissues to expand rapidly and create a DCS. Warming your skin quickly fools your body into thinking it is warm so it changes the way it regulates its temperature; blood vessels will dilate, shivering will stop and this is a bad thing as the human body is very good at warming itself at the correct rate.