Re: Inflatable PFDs in the south: Manual or Automatic?
The most popular vests all use an "aspirin" tablet that dissolves on immersion, alloing a spring-loaded firing pin to puncture the cartridge. Yes, under long exposure to high humidity those are infmaous for getting soggy and letting go, the same way that a real aspirin tablet degrades in a damp place.
The alternatives are the paper-mache wound bobbins used by only a few makers (like Crewfit) and the so-called hydrostatic release vests, which use a spring-loaded flapper valve to seal off the activator. This means the activator should not be exposed to ANY ambient moisture, until the vest is actually submerged, and the flapper valve opens, admits water, and inflates the vest.
In a USCG approved vest I think you'd only find the "hydrostatic" vests, Crewfit are in the UK and seem to have ignored the US market.