I was just thinking recently about submarines, and how long they can
stay submerged.
I did some sums relating to the amount of oxygen a person uses every
day, the published crew figures for such vehicles, etc., and basically
got stuck.

So can anyone help me understand how long submarines can stay
underwater, and how they manage the oxygen / carbon dioxide during
this time?

With thanks in advance for all answers.

Hello Notionalinquirer

The main limitation to how long a submarine stays under water is now
not the air that they breathe but actually the food that the
submariners need to eat!

A nuclear submarine can easily stay submerged for several months at a
stretch but there is a limit to the amount of food they can carry as
this has to be brought along on the mission.

Nuclear submarines can produce its own oxygen supply from the water
that surrounds them and there is plenty of that down there!  Like the
International Space Station it has generators that use electrolysis to
split the water molecules into the oxygen for the people to breathe. 
They also carry emergency oxygen cannisters should there be a problem
and they need to surface.

The carbon dioxide and toxic gases that build up within the submarine
are adsorbed onto scrubbers that clean the air, again similar to how
the International Space Station does this.  A simple air scrubber is
soda lime which traps the CO2 from the air.

A very good summary of how subamrines work can be found here:
http://people.howstuffworks.com/submarine2.htm

Similarly a US Military FAQ on this subject can be found here (Q17):
http://usmilitary.about.com/library/milinfo/blsubfaq.htm

If you have any further questions regarding this subject please ask
for clarification and I will do my best to help.

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Request for Answer Clarification by notionalinquirer-ga on 15 Jun 2004 05:09 PDT

Thank you for such a rapid and thoughtful answer.

I have also checked the websites you refer to, from which I have
included the following extract:

Historically, diesel-powered submarines operated internal-combustion,
air-breathing engines on the surface or just below the surface by
using a snorkel mast (snorkeling). When completely submerged, a
diesel-powered submarine uses its battery power and electric motors
for propulsion. Depending on speed and other battery use, the
submarine could stay underwater for up to several days before
recharging batteries and exchanging stale air for fresh air.

there are still some points about which I am puzzled: in particular,
(1) does the oxygen supply *never* act as a constraint,
(2) do the same points you have described apply to (eg civilian)
non-nuclear submarines

Thanks in advance.

---

Clarification of Answer by palitoy-ga on 15 Jun 2004 06:16 PDT

(1) Does the oxygen supply *never* act as a constraint?

The oxygen supply would only act as a constraint on a nuclear
submarine should the food supply run out or if there were major
problems on board.  By major problems I mean that the oxygen
generation system failed *and* the backup system of oxygen cylinders
became used up.  In these cases I believe the submarine would surface
as soon as possible.

(2) Do the same points you have described apply to (eg civilian)
non-nuclear submarines?

For civilian submarines the length of time the submarine stays
underwater would depend on the submarine type.  Some submarines will
be fitted with oxygen generation equipment, some will not.  Some will
have oxygen supplied by cylinders only, in which case the oxygen
supply will last only until the cylinder runs out.

THX1138-ga is correct, as were you, in stating that CO2 build up is a
major concern within the submarine but again if the correct equipment
is used in the ventilation system the problem is fixable.

---

Clarification of Answer by palitoy-ga on 15 Jun 2004 06:29 PDT

Some further links for you on the technical effects of carbon dioxide
in submarines and air purifiers:
http://antoine.frostburg.edu/chem/senese/101/environmental/faq/co2-recycling.shtml
http://www.rnreference.mod.uk/09/inm/subs.htm
http://www.madsci.org/posts/archives/apr2002/1017840072.Eg.r.html
http://www.naval-technology.com/contractors/hvac/molecular/
http://www.chinfo.navy.mil/navpalib/cno/n87/usw/issue_9/sub_rescue.html
http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/carbon_dioxide/health_cd.html
http://www.naval-technology.com/contractors/hvac/dornier/index.html

---

Clarification of Answer by palitoy-ga on 15 Jun 2004 06:30 PDT

In my previous clarification that should read "food supply NEVER run
out" not "food supply run out".

Hello notionalinquirer

I haven't researched your question, but it is my understanding that
the main problem with recycling air is not the loss of oxygen in the
exhailed air but the build up of carbon dioxide, it is the CO2 that is
the real problem as high levels become toxic.  Some submarines use CO2
scrubbers that remove the CO2 and make the air breathable again.

With regard to civilian subamrines see:

"Life support - 16 CO2 scrubbers, 24 hours O2"
http://www.sub-find.com/v48.htm

Best regards

THX1138

Hello again notionalinquirer

Some other snippets for you:

"Submarine occupants exposed to 3% CO2, 16 hours/day for several weeks
experienced flushing of the skin, an impaired response of the
circulatory system to exercise, a fall in blood pressure, decreased
oxygen consumption, and impaired attentiveness."
http://www.intox.org/databank/documents/chemical/carbdiox/cie747.htm

"What Sewell can describe without breaking security is generalities,
such as what it's like to spend as long as two months underwater,
dropping down to the ocean floor.
"We manufacture our own air, water and light. You learn to appreciate
fresh air and sunshine," he said. "Sometimes people panic from close
quarters."
http://www.sid-ss.net/ntins/bbs-049a.htm

"The USS Trinton stayed submerged for 84 days travelling almost 66,000
kilometers when it circumnavigated the globe in 1960"
http://www.historytelevision.ca/archives/subWeek/quickfacts/

"When I was in the military I worked in a nuclear powered submarine
where we'd be submerged for three months doing very dangerous things"
http://www.usc.edu/hsc/info/pr/1vol7/704/giant.html

Best regards

THX1138