Wasp Disables Tractor-Trailer
Wasp Disables Tractor-Trailer
A tractor-trailer traveling on an interstate, hauling a load weighing an estimated 50,000 pounds, suddenly catches on fire.
The culprit? A single wasp.
Science fiction? Was it the legendary Avenger character created by Dr. Hank Pym? Was it a genetically modified wasp? No, it was just an ordinary yellow and black striped paper wasp that was responsible for disabling and causing significant damage to a tractor-trailer.
And now, the rest of the story...
I was retained by a national tractor-trailer fleet manager to determine how and why a trailer hauling a valuable load was disabled and damaged. It was reported that as the tractor-trailer was traveling down an interstate, a vehicle passing by noticed smoke coming from the trailer and signaled the driver to pull over. A fire ignited at one of the wheels was extinguished, and the trailer towed to a nearby yard.
Initial examination revealed that the trailer wheels were heat and fire damaged due to unintended brake application while in transport. As we know, traveling with brakes applied can create sufficient friction/heat to ignite nearby combustible materials such as tire rubber. Fortunately, the fire was extinguished soon enough to leave the braking system, including combustible air hoses, intact allowing the air brake system to be charged with a compressor and examined.
In examining the air brake system, consisting of air hoses and relay valves, air was applied to the supply side (emergency or red line) gladhand connection located at the front of the trailer [Figure 1]. Gladhand connections are where supply airlines are connected to the trailer and resemble a pair of hands shaking when connected. Upon application of pressure, the reservoir tank would be expected to fill and pressure increase thereby disengaging the brakes.
However, when applied to the supply side, air exhausted from the service (blue) side, a clear indication that a problem existed with the SR-5 relay valve. Relay valves containing multiple ports/valves, are used to apply and release brakes, and are installed close to an air tank near the brakes. The SR-5 relay valve was removed for examination [Figure 2].
The SR-5 relay valve was disassembled, and debris was found in a spring-actuated valve seat. The debris was found to be parts of a paper wasp [Figure 3], which held the valve seat in the open position. With this valve open, the air pressure needed to keep the braking system in the off position while driving will bleed off, causing the brakes to be applied while driving. A single paper wasp had entered the gladhand opening in the front of the trailer and then became lodged in the SR-5 relay valve, disabling the trailer braking system.
Why did the wasp enter the gladhand entry point to the airbrake system? Paper wasps feed on flower nectar. The gladhand openings at the front of the trailer are colored blue and red and, to a wasp, might look like a tasty, nectar-filled flower. Gladhand manufacturers recommend that a screen cover be applied to these open ports for just this reason. That “flower” turned out to be an expensive meal for both the wasp and the tractor-trailer.
About the Author
Anthony (Tony) A. Yurko, III, M.S.M.E., P.E., CFEI, CVFI is a Consulting Engineer in our Cleveland, Ohio Office. Mr. Yurko provides consulting services in the areas of vehicle accident reconstruction and vehicle systems analysis; mechanical evaluation of damage to machinery, equipment and component systems; and fire origin and cause determination. You may contact him for your forensic engineering needs at tayurko@edtengineers.com or (440) 239-0362.
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