An inflatable life jacket is a bladder and a CO2 cylinder with a firing mechanism, folded into a collar. It's comfortable enough that people wear it, which is the point. It also fails quietly: Transport Canada warns that an unmaintained jacket may not inflate at all.
What fails
The arming. A cylinder that's worked loose, been fired, or rusted won't inflate the bladder. Most jackets show a service indicator: SAIL's Adam Cort says green means armed and red means it can only be inflated by mouth.
The bobbin or cartridge. Auto-inflating jackets fire when a water-sensitive bobbin dissolves. Transport Canada says humidity and heat affect it and that it should generally be replaced within three years; Mustang Survival prints an expiry date on its bobbins. Cort says to replace one more than three years old even if it looks sound.
The bladder. It leaks with age and wear. Mustang says a leaking PFD will not hold its firmness and should be replaced.
How a surveyor checks it
Count the jackets against the crew the boat is used with. On each one, check the indicator is green, the cylinder is screwed in and free of rust, and the bobbin or cartridge is in date. Look at the bladder, stitching, webbing and buckles for damage and mould. Read the care label: Mustang says the annual inspection should be recorded on it in permanent ink. Ask whether a re-arming kit for that make and model is on board, as Transport Canada recommends.
What decides the grade
Whether each jacket would inflate. A red indicator, a fired, loose or corroded cylinder, or a failed bladder is an A. Out-of-date bobbins or no service record is a B. Jackets in date with no leak test recorded are a C.