Exploding drive shaft!

[jfdtraining]

Responding to a motor vehicle accident on 12/11/06. On arrival had a Ford Ranger on it's top with the passenger compartment and running gear completely involved in fire. As we started to put the pre-connect in-service a very loud explosion was heard, guessing a tire or a shock we extinguished the fire and didn't think anything else about it. That is until the vehicle was uprighted and was being loaded on the flatbed. We noticed that the driveshaft had undergone a violent rupture that had put a very nice tear in the casing. These new vehicles have gone to much lighter density metals for the drive shaft(alumnium/magnesium) to lighten the load of the vehicle and keep the same shaft integrity. What would cause this to explode so violently? Is there some type of pressurized gas inside or something to insulate or cool the shaft?

Scott Sanders
Lieutenant
Jefferson Fire Department

[LeeJunkins]

No sir they are not pressurized, This has been an infrequint happening for many years and because of that we fail to teach it enough in class.
It is very common in big truck fires.

A drive shaft is a sealed tube, inside the tube is traped air just like we breath 78% nitrogen, nitrogen has a very high rate of expantion when exposed to very little heat, This is the same thing as the airbag canisters in fire only not as extreme, when the nitrogen expands to a point that it has no more space something has got to give.

This is the same process that makes an airbag work, When a small charge is set off in the canister the nitrogen or argon expands so fast that it fells the air bag in about 6 millionths of a second.

[jfdtraining]

Thanks for the enlightenment. Guess thats just something that gets overlooked. It sent parts flying everywhere. Thanks again.

ss

[LeeJunkins]

Just a note: When I was studying, putting my Big Truck Fires class together I talked to one of the engineers at Peterbuilt about this and I ask him why they did not drill a vent hole in each end of the shift to keep this from happening, and he told me that believe it or not the air sealed inside expands enough at normal temp to make the shaft stiff enough not to vibrate, he said to start a truck in sub zero temp and drive it down the road as the temp of the drive train goes up you can feel the truck level out. Or tap on a cold shaft and hear the ring and then warm it and see the difference in the sound.

[AC1503]

Lee, I believe that you have interchanged the percentage of Nitrogen in the air with the percentage of Oxygen. Oxygen is about 21%, while Nitrogen is a little over 78%.

[LeeJunkins]

Lee, I believe that you have interchanged the percentage of Nitrogen in the air with the percentage of Oxygen. Oxygen is about 21%, while Nitrogen is a little over 78%.

Hey I am an old man lieve me alone, Yes I did, it's been along day.
But I did get out what I meant to say and at 78% you can see even more potential for explosion.

Go back and read it I said 78% ( thanks to the Edit Button)

[AC1503]

Lee, I see that you did say 78%. I'm terribly sorry to have not read your post correctly. I'm an old man myself & fat too, so I understand. An email to you would have been the better choice to mention it in the first place.

Take care Brother.

[LeeJunkins]

I am one that is never ashamed of saying I am wrong, if you make no mistakes you are not doing anything. But if you slow down a little you don't make as many.

[slackjawedyokel]

Saw it in a rolled over Bronco 2 also.