Albro wrote:
Well, what confuses me is that what cause the explosion by using a oversized cooking-pan is that it heats the canister thus increasing the pressure.
So why dont the saftey-valve shut of the gas?
Many of the so called shut off valves are not always effective, and this led the Australian Govt to ban many of the stoves and put some legislation in place ensuring that the safety valves conform to Australian standard. So many of the stoves bought here are "spurious" However even if the valve works and you are using the superior CRV equipped cylinders explosions can still occur if the cartridge is incorrectly seated in the stove.
Story of exploding stove below investigated by Chemaxx
The aerosol type butane canister was equipped with rim vent release (RVR) devices and the
evidence indicated that the canister dome had expanded and the RVRs did in fact activate. It was experimentally determined that the dome expands and the RVRs activate at a pressure of 200 psig, which corresponds to a temperature of 200-225°F. In spite of the RVRs activating, the dome and body of the canister did separate.
When the incident stove was examined (with all parties present) it was determined that the main control knob on the front of the stove was in the OFF position.
It was also determined that the safety shut off valve (SOV) had activated. The SOV is designed to turn off the flow of gas to the burner in the event that the butane pressure reaches 70-80 psig.
The finding that the SOV had activated begged the question: How did the canister reach the 200 psig needed to expand the dome and activate the RVRs if the SOV activated and shut off the gas (and hence the burner flame) at a pressure of 70-80 psig?
Even after the trauma of the fire and explosion, the SOV and the main control valve on the evidence stove were tested and found to be functioning reasonably well. All parties agreed that the butane canister did not show any manufacturing, mechanical or metallurgical defects that could account for the explosion. Tests on exemplar canisters showed that the canister would withstand exceptionally high pressures without bursting.
Why it exploded
The plaintiff's theory was that the design of the canister and stove allowed the canister to be inserted incorrectly by ¼ turn such that the exit tube inside the canister was pointing toward the burner instead of the sky. It was hypothesized that this resulted in "erratic burning" which in turn heated the canister and caused it to explode. This made sense on a qualitative level because the ¼ turn configuration would eliminate the "evaporative cooling," at least for a while. However, when this hypothesis was experimentally tested, the heating phase only lasted until the liquid level fell below the internal exit tube, at which point evaporative cooling returned. This is demonstrated in the animation below that uses actual experimental data.
Full article here
https://www.chemaxx.com/butane_explosion2.htm