on some TV show about sharks I saw a long time ago there were these people working on shark repellents and they needed some sort of device that could hold a bunch of test repellent under pressure and spray it out in a controlled manner. Without spending money on some custom thing. So they used fire extinguishers. Filled them with shark repellent and took them underwater to spray in the general direction of sharks. Nothing more awesome than scuba divers using fire extinguishers underwater!
