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SOSpenders autoinflate in rain?
The guy behind you in the shop is right.
Just watch that thing during the rain, and after it.
As far as I am informed, there are two Automatic inflation mechanisms.
The one used by Sospenders, which consists of a salt bobin that when in contact with water (or humidity) dissolves itself, and triggers the mechanism which actuates on the Co2 cilinder inflating the pfd. This salt bobin, has a one year life expectancy. But when the pfd has been used in heavy seas or rain for a long period (long period in my experience is more than 8 hours), and you find the thing wet as your gloves, you can expect it to autoinflate any time at all.
After having such experience a couple of times, After 4 or 5 hours I instruct the crew to desarm the bobin, and store it inside.
Crew must also pay attention to carefully assure that the velcro closing system which enclosures the red pull tab, is securely fasten. Crew rushing on deck may accidentally open the velcro and let the red tab get caught in any piece of equipment, (a cord, block, or whatever), and manually inflate the thing as well. Last time happened to me with the wheel steering, in a 50 knt blow. I assure you that with that thing inflated on board, you are a handicapped, unless you are able to take it off.
After rain stopped, you must check thet the pfd are desarmed, and the bobin stored in a dry bag. SHould you live the pfd armed, humid, they will autoinflate, hours or days after, but they will do. My concern has been always wether those bobins exposed to high humidity where still in good service. I will tell you, that I''m not going to do the test. I just don''t use them any more.
The other automatic system, consists of a mechanism known as Hammar hydrostatic,
which actuates under water pressure.
You can find additional info on this
or googleing "hammar".
This mechnism is used by the Crewsaver pfd.
By the time I found this tech notes, I had already bought 8 sospenders and its replacements kits. So, since they all have a built in arness, we no longer use them with the bobin.