Davis Submersible Escape Apparatus

[Gerard Peels]

Dear All

Although being a diver myself I am not familiar with all the details of this DSEA and the onboard policy - instructions within the RN, somehow the following questions popped up:-

1) Where these gadgets on a 1 to 1 base per crew member on board the subs, e.g. like nowadays the life vests on an airplane, you dont even board if there isnt one available under your seat?

2) was there over time a technical development during 1939-1944 of this DSEA and how did these delvelopments look like?

3) Supposing that these gadgets were rather a nuisance to wear while under normal circumstances and on duty, where were these gadgets stored?

4) are there any statistics about these DSEAs?

Thank you

gerard

[John Brown]

Gerard

Can't help much other to say that a small version of this device was developed to help escape from sinking Duplex Drive Tanks such as those used in the Invasion of Normandy.

It was called the 'Amphibious Tank Escape Apparatus'


Regards...John

[Kevin Denlay]

Assume you have seen this web site?

K

http://www.subescapetraining.org/History.html

[Gerard Peels]

Kevin
Thanks for your link. I was aware of that page, but I hoped to get also an answer on the other questions.

I am not a person belonging to the medical profession, but consider the following situation when a sub sinks at a location where the sea has a depth of about 100 -140 m, maybe less, which means that in an enormous tempo the crew had to:-
1) either grab the DSEA, donn it, enter a lock/tube, fill it with water, open hatch and surface, or
2) wait until compartment was flooded with water and probably leave through hole in hull, or
3) they were on deck while leaving Malta in darkness...Btw Does any one knows the time the sub departed ?

Anyway. where I am after is, that even using this breathing aparatus and inhaling pure oxigen as described on your refered webpage, this oxygen becomes toxic after a while (and I guess) that spasms would evoke spitting out the mouth piece...in other words: not much time was left.

As it seems this breathing aparatus was mounted on the chest and did not form a part of those modern "let's call them plastic bags" where one steps inside completely.

Knowing the water temperature in May around Malta to be about 18 degrees C, as a logical consequence having to swim back 6 -7 miles to shore is rather unlikely, if one's body is directly exposed to water. Exhaustion and hypothermia would come in and diminish the likelyhood of survival.

Would anyone have suggestion concerning this argumentation?

Thnx

Gerard

[Kevin Denlay]

Originally Posted by Gerard Peels

Anyway. where I am after is, that even using this breathing aparatus and inhaling pure oxigen as described on your refered webpage, this oxygen becomes toxic after a while (and I guess) that spasms would evoke spitting out the mouth piece...in other words: not much time was left.

Hi Gerard

As mixed gas (and closed circuit rebreather) divers we are taught that oxygen becomes toxic when higher than 1.6tata/bar. That’s 6m if diving on pure o2. However we are civilians. Military uses to 9m regularly and even deeper (classified I am told) on ops. I also know personally Ab divers (abalone divers) who worked collecting Abs at 12 to 15m(!!!) in cold water breathing oxygen, and they are still alive to tell they tale, although I am not sure how or why. In dry chamber treatments for decompression illness you will be breathing oxygen at at least 2.8ata/bar which is the equivalent of 18m depth. Of all the treatments they do, not many people fit. But you are dry in a chamber, not wet, and this has been proven to make a difference.

The onset of symptoms leading up to an oxygen convulsion can be slow, or extremely rapid, depending on the individual and other circumstances. Working hard, cold water, co2 build up, etc are all precursors to an o2 fit. (Basically like a Grand Mal Seizure.) And you are correct that once fitting (in water) the diver loses the mouthpiece and he or she generally drowns. (It’s not the fit that kills you, it’s the drowning.) And sadly, there have been numerous occurrences of this happening in the recreational rebreather diving world in the last, say, ten years, since closed circuit rebreathers moved out of the military ‘sphere’ and into the recreational sphere.

However, if one was to leave a sub and go directly to the surface the chance of a fit I would think is small, but certainly far from non existence. (But still worth the risk as opposed to staying in the sub though!) However I am no expert, and I have also seen a person die right in front of me from accidentally breathing pure oxygen at about 78m (yes 78m or 8.8ata/bar!). Not nice and it happened in well less than a minute from when he started to breathe it (unnoticed and by mistake of course.).

Should you be really interested in the effects of oxygen under pressure then I suggest the book Oxygen And The Diver by Kenneth Donald. Covers many many tests done by him/military in UK during WW11 when they were trying to find the limits of O2 diving. The book is a serious eye opener to see how different people/divers were affected differently by breathing oxygen (at the same depth/pressure) and/or how on different days the same person would be affected differently also.

It would be an understatement to say that to stay alive as rebreather divers we have learnt to treat oxygen with the UTMOST respect. However, by the same token, if it meant drowning for sure or maybe surviving (and escape from the sub) I would breathe it an any depth to try to make that escape.

K

[Gerard Peels]

Thank you Kevin

A little bit more. Normal recreational diving accepts "only" 1.4 bar ppO2 (PADI).

In humans, there are several types of oxygen toxicity:

1. Central nervous system (CNS) oxygen toxicity (see your dive computer .e.g Aladin)
2. Pulmonary oxygen toxicity
3. Retinopathic oxygen toxicity

As far as CNS is concerned:- ".. divers are taught to plan and monitor what is called the "oxygen clock" of their dives. This clock is a notional alarm clock, which "ticks" more quickly at increased ppO2 and is set to activate at the maximum single exposure limits recommended in the NOAA Diving Manual. The maximum single exposure limits recommended in the NOAA Diving Manual are 45 minutes at 1.6 bar, 120 minutes at 1.5 bar, 150 minutes at 1.4 bar, 180 minutes at 1.3 bar and 210 minutes at 1.2 bar, but is impossible to predict with any reliability whether or when CNS symptoms will occur"

Text Source: http://en.wikipedia.org/wiki/Oxygen_toxicity

It is rather an intersting view upon the differences in policies, theories and military or recreational practise.

I seldom dive using Nitrox....

any anaestisist could tell you more concerning these effects

Gerard

PS. what is your maximum depth?