Anything ‘could’ go off accidentally, but IMO a mechanically fired extinguisher is less likely! If anyone has ever tried to set off a hand held they will know how hard you have to hit the fire button for it to work..... Biggest problem will be the pull cable seizing up with water ingress, and I'm sure many of us have had that at scrutineering!
The fix is to make sure to only use stainless cables, and put some lube down occasionally....
