4 replies to this topic

[hrun]

Hello everyone! New member, not a professional or even hobbiest pyrotechnician, but hoping I can get an answer to a pyro question.

In the movie The Abyss, Bud lights a flare during his long underwater descent, after his lamps implode from pressure. (I'm referrring to the pyrotechnic flare while he's still falling, not the cyalume light stick he uses when he reached the bottom.) Underwater flares have apparently been used in other movies:

http://www.mail-arch...m/msg00106.html

and I've found a mention that Cousteau used underwater flares during cave dives:

http://www.bec-cave....p;limitstart=14

Underwater flares don't seem to be available any more, Pains Wessex certainly don't seem to advertise them, so I was wondering where the movie makers get theirs from, and how they work?

I'm quite aware that a flare composition will contain its own oxidiser, I was more concerned with the mechanism for overcoming the heat losses to the water. It occurred to me that a composition that gave gaseous combustion products could generate its own "gas shield" for the burning flare. Alternatively, a very high energy composition might simly maintain a steam layer and so reduce the heat transfer rate. Both of these could be expected to be less effective as the pressure increased with depth.

[Ritual33]

I would also like to know this, I love flares.

Regards,
Drew

[fishy1]

I liked that film.

I would imagine it's be a metal powder, probably magnesium or a mgal alloy, and a fairly strong oxidiser, barium nitrate or perc or similar, with some kind of binder.

[BrightStar]

Flares are one of my favorite topics Underwater flares are much like ordinary hand flares from what I've read by Ellern and others. A white comp for use in air might be approximately 55% atomised magnesium, 40% sodium nitrate, 5% laminac (polyester) resin binder. This is pressed into a steel tube.

This, like most flares, is fuel rich. The excess magnesium burns in the surrounding air. To modify for underwater use, you would balance with more oxidiser and less fuel to be roughly stoichiometric.

To quote Ellern, 'Hand-held underwater flares for use by divers differ from other types by their battery operated, self-contained initiator protected by a rubber diaphragm. The flares, according to a commercial pamphlet, burn at one or two minutes and furnish 80,000 cp. They can be used at 100-ft depths and lower, and are useful for underwater inspection and exploration - not to mention their popular appearance in some television programs.'

There are two mechanisms for light emission. Firstly there's the molecular spectral emmision of the vaporised combusion products leaving the flame front at >2000 centigrade. Sodium nitrate is sometimes used despite its hygroscopic nature whereas potassium nitrate is not - the yellow lines contribute significantly to the light output. Secondly, as the vapours condense, you also have the black-body type radiation from the fine, hot particles of magnesium oxide and other solids exiting the flare.

I would imagine that the surrounding water might reduce the flame area available for luminous emission but you could probably tweak the mix to compensate.

Ellern mentions only one specific formula for underwater use, mostly because it is of interest in using a sulfate oxidiser:

Underwater Flare - Ellern no 36
Magnesium 16%
Aluminium 12%
Barium Sulfate 40%
Barium Nitrate 32%
Binder: 8 parts linseed oil, 1 part manganese dioxide

This was intended to silhouette submerged submarines in WWII but was 'not tactically useful'...

Edited by BrightStar, 21 March 2007 - 06:23 PM.

[lew]

Nice.

I watched the abyss not that long ago. I think that flare was being used at 20ish thousand feet!! thats just short of 9000 PSI!!

That is some quality flare!