Getting DCS on short but deep ascents?

[Lenaxia]

This is more out of curiosity than anything else.

Is it possible to get bent doing a short (say 20ft) ascent quickly at depth?

For the purposes of this question, lets define quickly as around 90ft/min (triple the recommended ascent rate), basically swimming with urgency but not sprinting.

For instance, if someone was at 200ft and quickly ascended to 180ft then remained there, is there a risk of DCS?

My understanding tells me yes but its so mild that it isn't going to be of great concern. The ascent limitations are mainly for longer distance ascents to the surface.

Does this change for saturation diving? I can imagine for instance, commercial divers need to move up and down and all around structures with due haste while working.

 

[TSandM]

Well, a lot of it depends on proportional pressure changes. You are going to be in less trouble ascending fast from 200 to 150, than you are from 50 to the surface, in terms of proportional pressure changes. Of course, that also depends on the time you have spent at depth, and which theoretical compartments are most heavily loaded. The fast compartments, according to theory, tolerate higher overpressure gradients, so you are less likely to get in trouble with short, deep dives than with longer, moderate depth ones.

 

[Duke Dive Medicine]

This is more out of curiosity than anything else.

Is it possible to get bent doing a short (say 20ft) ascent quickly at depth?

For the purposes of this question, lets define quickly as around 90ft/min (triple the recommended ascent rate), basically swimming with urgency but not sprinting.

For instance, if someone was at 200ft and quickly ascended to 180ft then remained there, is there a risk of DCS?

My understanding tells me yes but its so mild that it isn't going to be of great concern. The ascent limitations are mainly for longer distance ascents to the surface.

Does this change for saturation diving? I can imagine for instance, commercial divers need to move up and down and all around structures with due haste while working.

Lenaxia,

Good question. From a practical recreational/technical diving perspective, it's generally not possible to get DCS in the manner you're describing as there isn't enough of a pressure change to cause clinically significant bubbling, despite the rapid ascent rate. A tech diver who's at 200 feet will probably still be taking on inert gas at 180 feet.

Chapter 15 of the Navy Diving Manual (available for download here) contains specific guidelines for saturation diving excursions. In your example of a diver at 200 feet, the shallowest excursion depth is 135 feet, provided the divers had been at 200 feet for at least 48 hours. They don't perform ascents at rates like you're describing, though, and for a saturated diver, a very rapid ascent to the shallowest excursion depth could theoretically be a problem. Here's a study from 2000, where the investigators saturated pigs to anywhere from 50 to 150 feet and then decompressed them at a rate of 30 feet per minute, which isn't rapid but it's the closest comparison I could find.

Natural history of severe decompression sickness a... [J Appl Physiol. 2000] - PubMed result

 

[Dr Deco]

Hello Lanexia:

As mentioned above, it is the depth of the pressure change that matters in these cases. Big changes are possible with deep dives. When I was at Ocean Systems in the early 1970s, we did experiments with a saturation “holding depth" of 500 fsw. The divers then made deep dives to a working depth of 1,000 fsw for about a half hour. They then ascended, without any stops, back to the holding depth [500 fsw]. That was a change of 500 fsw and no problems were ever encountered.

Now, that is a jump! :shocked2:

Dr Deco :doctor:

 

[Lenaxia]

Thanks for the replies everyone and for humoring my curiosity. I doubt if any of this info is really applicable to any rec or even most tech divers but it was definitely interesting!