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Fire and Explosion of Products.

For better understanding in explosion, BEAR engineers have conducted more than 100 explosion tests. The picture on the right shows the sequential frames of explosion test of a 5 gallon Blitz consumer gasoline container which had 500 ml of aged gas. When the gasoline was poured over a flame, the can exploded right away, producing the typical explosion sound that can be heard from several blocks away.

 

In some cases, however, the can does not rupture and a jet of burning gasoline is ejected from the container, as shown to the right in sequential frames of the jetting test. Notice the flame halfway up the translucent spout in the first frame.

  

Our work has also shown that an inexpensive flame arrester would prevent these explosions. BEAR Engineers wrote a paper about importance of flame arrester.

  

Using this experience, BEAR Engineers compiled and published a peer reviewed paper about how to prevent explosions of portable plastic containers.

thermo limit switch

  

A large fire occurred in an office building in Downtown San Francisco. After the fire was put out, investigators looked for the origin of the fire and suspected an area where two heaters with over 600 K BTU output were located. The heaters were brought to the BEAR Lab, and a joint investigation occurred. The heaters were hooked onto a special gas line and tested. After a test protocol was established, the thermo limit switches were tested in our lab (see picture to right). Further investigation confirms that the thermo limit switches were operating inaccurately.

 

   

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portable plastic gasoline container explosions

  

Portable plastic consumer gasoline containers explode when users unexpectedly provides ignition sources. Ignition sources vary from spilling gasoline on hot equipment to splashing hot embers, thought to extinguished, to static electric sparks from rubbing the container on clothing. BEAR’s combustion laboratory has accumulated data of the conditions (e.g. temperature, amount of gasoline and weathering) that will result in an explosion. When explosion accompanies liquid gasoline, it is particularly dangerous as liquid is often thrown on the user and/or persons nearby and causes extreme burns, disfigurement and death. The explosion of the container leaves rupture marks that are on any edge, seam or thin spot as it can be seen in pictures on the right.

weed wacker
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A commonly used handheld week wacker experienced a mechanical failure of the commutator (red arrow) which set the wacker on fire. Sooting (blue arrow) indicates the fire traveled through the windings to the plastic case.

leaking fuel lines

  

BEAR has extensive experience performing mechanical analysis when investigating the cause of fire. One example is the automobile caught on fire, which is shown on the right. After the inspection of the van, BEAR engineers found out that the fuel lines leading to the fuel injectors had been leaking due to a faulty fitting design.

propane powered pickup truck

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The truck shown on the right was involved in a head-on collision in which the driver was severely burned. BEAR engineers found that all the piping attachments were located on the front of the propane tank and were broken off during the crash as the tank pushed through the back window of the cab. BEAR's investigation showed that other trucks that had the tank piping attached to the bed side of the tank fared much better in similar crashes. 

water heater fire
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Water heater fires are most commonly caused by combustible material that has been stored next to the water heater. Newspapers, paper bags, and cardboard are typical of the materials found in these cases. Less common are the fires caused by leaking supply lines, blocked flues, clogged orifices, and faulty control valves. The picture on the left is the water heater that was caught on fire.

barbecue grill

 

Investigations of barbecue fires at BEAR indicate two common sources of fire. First, the hose from the tank to the barbecue fails due to wear and tear or abuse, and the escaping propane then ignites via the barbecue flames. Second, the barbecue propane tank is overfilled with over 85% being liquid propane. Tanks can then be over-pressurized on hot weather because liquid propane thermally expands more than a steel tank. The over-pressurization causes a propane release through the tank pressure relief valve. The 15% vapor space in the tank is a reserve for the liquid to expand without over-pressurizing the tank.

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