Fire on a submarine?

[Pix]

I'm watching a series with the kids and as I usually do I point out things that probably wouldn't happen in real life (or what would actually happen if they did do that which isn't shown) but I did that yesterday and wasn't sure if I was right or not.

Long story made short, it's WW2, a submarine has been stolen from the Nazis and being taken to the USA and they're being hunted by the Nazi navy. To top it off they're running low on air and while this was partly because of damage that sunk them and they'd since made repairs and were moving again (but didn't dare surface yet) one decides to set fires to terrifying Nazi research that they don't even want the American government to have either (in full view of the skeletal Navy crew). I said that fire was one of the worst things feared when in a sub (don't recall where I read or heard that, however) and that if they were low on air they most certainly wouldn't be setting any fires, not even just to burn a few papers.

But after that I was uncertain and thought I should verify. I know a couple of regular posters on this board have been in the Navy (I think a handful actually), and others may know someone who is and that Navy person is home for the holidays, so I wanted to ask while I'm thinking: is it true that fire is an especially great fear on a submarine, and can a sub (especially in WW2) refresh it's oxygen without surfacing? (And bonus question: how long can a sub, especially WW2 sub, stay submerged without having to worry about refreshing it's air supply?)

[OrphanPip]

Some WW2 submarines as the war progressed had snorkels to get new air while staying underwater. Submarines at the time were not like those today, they usually stayed very close to the surface when submerged. They needed oxygen to run the engines too, since they were diesel, when underwater they ran on battery power that was very limited. Submarines spent the majority of their time surfaced like an ordinary boat. Given that they couldn't run their engines under water, I imagine an open fire would be a bad idea on a submarine because it would consume oxygen quite rapidly.

[Bowyn Aerrow]

Yep Snorkels provided air.

"Periscope depth" is the usual depth that a sub of that time would be running while underwater. Depending on when during the war this took place, it is possible they had air scrubbers (like using lithium to pull carbon out of the air) and they had better and better batteries for long term submersion. Late war that technology was catching on.

The Snorkel started being used near the end of the war. Prior to that the subs would submerge for short durations switching from diesel to battery power.

http://inventors.about.com/od/militaryhi...Subs_2.htm

Tells you more. The submarine did change over time during the war. Earlier models rarely went underwater, end war models spent a good deal of time underwater.

If they are burning just a pile of paper, the danger is rather low. If they set fire to a compartment then yes its a serious danger.

In this image:


The "pipe" to the left is the periscope, the pipes and attachment to the right is the snorkel.

I don't know if any of the old war movies depicted what happens after submerging, but a typical sub of the day would ping (send out a sonar signal) to see if any enemy were around and then the order to "open the bulkhead flappers and recirculate". This order was given to open the valves along the ventilation system. All compartments were water sealed and the ventilation system as well during the maneuvers to dive and during periods of being engaged with an enemy.

Fire is not a 'huge' problem in that its pretty easy to put out considering the lack of flammable stuff in a sub. However what is flammable burns and produces highly toxic fumes. The sub's design with hatches that are water tight also means that if fire suppression doesn't work they can close off a section and let the fire suffocate. They could quickly close off every section of the sub with bulkhead doors and ventilation flaps.

The 'unbelievable' part here would be that they were so deep in the water and running their engines to reach the point where they are running low on air. While the battery technology allowed for deeper dives, it limited the length of time being powered (with propellers turning) and not sucking in air.

Unless they were being closely chased by surface vessels all of that time. since the Snorkel did have a distinct radar signature, the Germans tried various methods to make snorkels radar invisible - the first attempts at stealth technology was used with mixed results.

But the reality would be that their batteries would run out before their air supply. I can't think of a way that they could forget to store air while running on the surface or near the surface on diesel and charging batteries.