Unless the fill for the accumulator was closed, heating would not result in an overpressure situation. It seems more likely that the flame impingement raised the temp. of the aluminum cylinder to the point where it lost structural strength. It would also seem prudent to plumb the pilot flame in after the shutoff, so that the pilot is extinguished if the valve is shut.

Yeah, that's what I thought. Dry Chem extinguishers aren't rated for pressure. They hold the chemical AND a small rated tank of pressurized gas (like a big Whip-It container). When you activate them, the "whip-it" pops and discharges into the main tank. The pressure in the tank forces the chem to a pressure valve that opens when it's positive inside the tank (this keeps the dry chem inside until needed).

The only ones that Don't work this way are CO2 and halon. Both of those types are pressure containers from the ground up.

I kept my mouth shut during the "small accumulator' discussion because I figured "fire extinguisher" was short for "CO2, pressure rated extinguisher". But, I guess not. And therein lies the danger. People who /know/ what they're talking about using shorthand around people who don't. Eventually they cheap out, and someone gets hurt.