HomeAboutNewsStaffClient ListContact Us
  Fire and Explosions  
  |Thermo Switch | Gas Can ExplosionsWeed Wacker | Leaking Fuel Lines | Propane Powered Pickup | Water Heater | Barbeques  

Testing Thermo Limit Switch


A large fire occured 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 occured. The heaters were hooked onto a special gas line and tested. During further investigation, the thermo limit switches were suspected to operate inaccuratly. After a test protocol was established, the thermo limit switches were tested in our lab (see picture to right).

.Thermo Limit Switch


Portable Plastic Consumer Gasoline Container Explosions


Portable plastic consumer gasoline containers can and do explode.  Engineers at BEAR’s combustion laboratory in Berkeley, CA have determined the conditions (e.g. temperature, amount of gasoline and weathering) that will result in an explosion.  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.  These types of explosion are particularly dangerous as liquid gasoline is often thrown on the user and/or persons nearby causing extreme burns, disfigurement and death.  Container ruptures have been found to occur on any edge, seam or thin spot, see pictures below:




We have conducted more than 100 explosion tests

Sequential frames in the 7-9-09 BEAR explosion test, 500 ml of gasoline, 22 F, 5 gallon Blitz consumer gasoline container are shown below. This explosion produced a very loud explosion sound that could be heard for several blocks.



In some cases, the can does not rupture and a jet of burning gasoline is ejected from the container as shown below in sequential frames in this 3-16-10 BEAR jetting test.  Note the flame halfway up the translucent spout in the first frame.


  Our work has also shown that an inexpensive flame arrester (a screen no finer than a window screen) would prevent these explosions. A simple metal screen flame arrester is shown on the right.



Our engineers have published a peer reviewed paper on the subject:


and have experience testifying on same issues


If you would like additional information, contact Dr. Glen Stevick, Ph.D., P.E.glen@bearinc.com or 510-549-3300 x1.


Other Fire Cases


Weed Wacker


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. Fortunately, in this instance no one was hurt and the fire was quickly put out.

weed wacker

This large brush fire was started by a weed wacker, that was used to cut brush. BEAR has examined many different weed wackers and has determined the cause of large fires

weed wacker.


Fire Caused by Leaking Fuel Lines


BEAR has extensive experience performing mechanical related fire investigation. One example is the van fire shown on the left. In this case, we determined that the fuel lines leading to the fuel injectors had been leaking due to a faulty fitting design.


Propane Powered Pickup

  The propane powered pickup truck shown on theleft was involved in a head-on collision in which the driver was severely burned. BEAR engineers found that, unfortunately, in this case, all the piping attachments were located on the front (cab side) 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 Fires

Water heater fires are most commonly caused by combustible material that has been stacked 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.  


  Investigations of barbecue fires at BEAR indicate two common sources: (1) the hose from the tank to the barbecue fails due to wear and tear or abuse; the escaping propane then ignites via the barbecue flames, or (2) the barbecue propane tank is overfilled. Overfilling the tank to greater than 85% liquid propane will result in an overpressure if the tank is exposed to hot weather (liquid propane thermally expands more than the steel tank). The overpressure 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 overpressurizing the tank.  
©2008 Berkeley Engineering And Research, Inc. All Rights Reserved.