Good question.

I think you'd need to look up the manufacturer of a specific product to get definitive answers.

Here's a link to one manufacturer. I've seen their products around but never used them. There's a link to the MSDS for the propellant here as well.
http://seasense.com/index.php?page=shop....t&Itemid=26


Here's a very interesting marine air horn that doesn't use a cannister at all. Might be better than any whistle out there.
http://seasense.com/index.php?page=shop....t&Itemid=26

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