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Portable Butane Stove Explosion #1

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Michael Fox, PhD.



Portable Butane Stove Explosion #1

One afternoon a middle-aged couple decided to bring home from their business a portable butane stove, as seen in the figure below.

New Portable Butane Stove

Butane Canister

According to the wife's testimony she was very familiar with the operation of the stove and had used stoves like this one many times before over 4-5 years and she had used this particular stove at least 30 times before. She was also aware that the canister had to be installed in a particular manner - with the alignment notch facing the sky.

A short time before 7:30 pm the wife placed the stove on a sidewalk in their back yard.

The wife was aware that she should not use any pans larger in diameter than ten inches. She placed a package of bacon and three sausages into a 10-inch diameter skillet. She then pressed the lever that moves the butane canister into position and then turned on the stove's main control knob to full open. Shortly after that she turned the control knob for the flame to medium. She testified that the burner seemed to be functioning in a normal manner and that the stove was clean.

After cooking a short time the wife got some sweat in her eyes and asked her husband to take over the cooking. At that time, the wife walked 12 feet away from the stove and had her back to her husband and the stove. After her husband had been cooking about 1-2 minutes she heard a loud explosion. The wife said that it was a total of 5-6 minutes from the time she began cooking to the explosion.

The wife testified that when she turned around, presumably immediately after the explosion, she did not see any fireball or flames. She was not aware of her husband having any problems with the stove before the explosion.

The husband was burned by the incident and taken to the hospital. While at the hospital he lapsed into a coma for a considerable time and eventually passed away. The wife had to close the family business and eventually lost their home.

The wife sued the portable stove company and the butane canister company alleging that both the stove and canister were defective. Chemaxx was asked to investigate the incident.

The physical evidence consisted of the incident stove and canister. The incident stove is shown below.

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.

Extensive experimental testing showed that during the correct use of the stove the liquid butane inside the canister actually becomes cooler in spite of the fact that there was a gas flame nearby. This is due to "evaporative cooling" as illustrated in the animation below that uses actual experimental data.

The following animations require the Adobe Shockwave for Director Plugin dowwnload here, OR is best viewed using Internet Explorer Browser.

The fact that the liquid butane in the canister becomes cooler during normal operation means that the pressure drops inside the canister with cooking time. Therefore, under normal operating conditions, the canister becomes less likely to explode with time as opposed to more likely.

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.

In fact, the heating phase of the ¼ turn scenario did not last long enough to even activate the SOV. Even if the canister had been installed totally upside down, the SOV would have stopped any continued heating. Keep in mind that the SOV shuts down the burner flame at 70-80 psig, which is long before the butane pressure reaches the 200 psig needed to expand the dome and activate the RVRs.

The primary Chemaxx conclusion was that there had to have been a secondary heat source and a secondary ignition source beyond the stove itself.

It was understood that the couple owned a full-size outdoor propane grill and the normal indoor cooking appliances, such as a gas kitchen range. It is unknown why they decided to use the portable butane stove on this particular day in lieu of their other, seemingly easier, options. Also, per the wife's testimony, it was the first time she had made bacon and sausage on the portable butane stove.

Furthermore, there were many residues on the stove that could not be attributed to bacon or sausage, plus some of the known residues from bacon and sausage were not found on the stove. Considering that the stove was clean before the incident, the evidence forced the conclusion that information was missing.

The case settled before trial.

Dr. Fox is uniquely qualified to investigate portable butane stove incidents. First, he has over 40-years experience in metallurgy, corrosion and failure analyses. Second, he is a Certified Fire & Explosion Investigator with over 25 years experience. Third, he has studied the failure of aerosol containers, such as butane canisters, for over 20 years. Lastly, he has investigated portable butane stove incidents for over 10 years.