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U500 Accident - Lessons Learned....

4K views 6 replies 7 participants last post by  The FLU farm 
#1 · (Edited)
Hi Guys,

I did a cursory search and did not find a thread on this. There are some valuable lessons and insights that can be learned from the Denio U500 Engine Rollover on July 10, 2016. The accident report has been released, and I think it can be a good learning tool.

The Accident Report can be viewed here: https://drive.google.com/file/d/0B74ZokMKPK3jZllKTFhpTlZKT2s/view?usp=sharing
(I tried to upload here but the file is 21mb)

Please keep posts respectful as 2 firefighters lost their lives in the accident when their U500 blew a tire and did a barrel roll at high speed.

Some of my takeaways:

#1 - Tire Condition is everything. Old tires at high speed in these vehicles is extremely dangerous. What is interesting to me is the number of discussions I have with customers who will argue this point when comparing costs of new tires against 10-15 year old surplus. Surplus tires have their place, especially trucks that are spending time strictly off-road at low speeds. Putting your set of weather checked 10 year old surplus tires on your truck and going down the freeway at 55-60 MPH should be assessed VERY carefully for numerous reasons.

We are currently giving opinion in litigation with an insurance carrier who holds the policy on a Unimog that was imported as a tractor, that was titled and registered for road use, that had tires 17 years old and was involved in a light/moderate accident. Once it is settled I will update with the specifics, but in todays world this IS becoming an issue. (Whats crazy in this situation is that the tires played little role in the accident.......but an keen adjuster is making the case that the tractor was not street legal based upon the importation type, and things such as the age of the tires.)

#2 - U500's and Rollovers. I would HIGHLY suggest those running a stock U500 with Cargo bed think about the implications here. In the case of the Denio rollover, the cab was the tallest point of the vehicle and the seat belt points in the door pillars were disintegrated by the force of the rollover providing no seat belt protection. (even thought the occupants were wearing them.)

I had some discussion last week with true Unimog experts at the Unimog display at Bad Kissengen. It was pointed out that the U500 does NOT meet European Rollover standards without additional ROPS protection installed. The fire body design in this case would not have been approved for road use in Europe as it did not provide the required ROPS protection. Regardless of the legal minutia I'm not so sure that a Fiber Cab with no rollover protection is a good option at freeway speeds.

Food for thought.

Cheers,

Scott
 

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#2 · (Edited)
Scott, thanks for taking the time to post this. The Accident Report is quite a read.

A sad and tragic event for the firefighters.

A couple of notes - To access the information needed to acertain the age of your tires, whatever the brand, purchased new or surplus, Steel Soldiers has a couple of threads on their site, which explain both the manufacturer's codes as well as the DOT codes. Google will get you there.

Many tires hitting the Surplus Market are less than 10 Years old, sometimes only a year or two old.
How the tires have been stored, in the sun or under cover, is an important consideration. The Surplus dealer "Might" have enough room inside to stack them up, But how did the Military store them ?

Some Interesting notes from the Report - The XZL 395 85R20's were load range G, so the load specs match the Goodyear MV/T's that I posted on the other Thread ( 9370 Lbs/Tire), not the Load Range J XZL 395's that I referenced (12,300 Lbs/Tire).

That size and specification of the XZL tire is 'Out of Production', and will be put back into production, when the demand dictates it.

The Report refers to the UNIMOG cab as Reinforced "Carbon Fiber". They might be right, but the the two damaged U500 Cabs that I examined first hand appeared to be a fiberglass / composite construction. Not that it matters, and maybe the material I saw (very fiberglass looking) was a type of Carbon Fiber that I am unfamiliar with.

This accident is not too different from the crash of the U500 that took place on HWY 50, west of Eureka, also in Northern Nevada.

Coincidentally, that vehicle was also travelling about the same speed, and suffered a catastrophic failure of the right rear tire. Fortunately, in that case the vehicle did not go into a barrel roll, but edged off of the high, beveled shoulder and sorta flopped onto the right side,as the right front tire hit the desert floor,doing a bit of face plant on the upper right corner of the cab. It came to an abrupt stop and did not slide across the ground substantially. The UNIMOG rode the berm for a while on the wheels, before hitting the flat and flopping. There were injuries, unfortunately, but everybody survived. The cab was cracked through in the area of the top right corner, and was a write-off, from what I understand.

The driver told me that shortly before, they had been driving in a mountainous section, with severe drop offs on the right, rather than the flat desert floor they landed on. This would have put them travelling east from Austin, Nevada, which lies to the west of the Toiyabe Range that defines the western confines of the Big Smokey Valley.

At the point that they left the Hwy, the road surface was well elevated, probably 5'-6', although it does not look like it in the photos. I walked up and down it on the day, and it is a good drop. It was an unlucky spot, in that the roadway is virtually level with the desert floor for long stretches through that section, and I think the driver might have been able to ride it out and keep it on the wheels, except for the high berm.

Thanks again Scott.

I think everybody should read the accident report,especially if you ever drive your UNIMOG on the pavement at highway speeds.
 
#4 · (Edited)
I saw absolutely no reference to the most important number, air pressure in the rear tires.
You've seen the formula for tire air chamber temp?
T(hot) = T(cold) X (P(hot) + 1 bar) / (P(cold) + 1 bar) all temps on an absolute scale
I never let T(hot) go over 171F = 77C = 350K; I got that number from a Michelin military tire rep at Eurosatory 2010
I run XZL+ in rear (supposedly slightly cooler than XZL)
I have drilled a 1" hole thru the center of each beadlock to ensure free communication of air betweeen the CTIS and tire air chamber; the driver of the Eureka truck thought that the tiny rectangular cutouts on the sides of the beadlocks might have squished shut
All my tires dated 2010 or later, I never buy even slightly used tires, and all are also rated at 161J (62mph)
I never exceed 59mph on GPS (60 on speedometer) except when passing
I run 95-101 psi cold in rear dependant on load (101-102 is as high as current CTIS "tire plug/chip" will let me pump up to)
I pay particular attention to tire pressure rise when AM start-out temp is 70F or higher
Just some advice from an old fart
PS I think the vehicle in the Eureka accident was using quite old XLs, which are speed rated at only 50mph.

Charlie
 
#5 ·
Am I reading the report correctly that the machine was running in excess of the rated tire speed when the failure occurred? I came way from the report thinking, but being unsure, that the 70mph vehichle rating/capability vs. the tires at 55mph rating was a contributor. I am not sure a new XZL would make it at 70 that long... Was the long term use over the rated speed a contibutor also, or is my impression of the rated speed thing wrong?

This is sad and tragic; my condolences, belated as they are, go out to the family and those affected.

Tires and, on the XBUs at least, the rear ebrake systems are safety critical. Loss of air at speed or loss of a tire results in loss of control.

C.
 
#6 ·
Initial documentation from Unimog NA lists the rated speed with those tires as 70mph. Subsequently the speed rating for the tire was downgraded across the board. I recently called Michelin Truck Tires NA to ask why and they refused to give "an answer" and standing firm on, to paraphrase, "the book is the book and what the book says goes". The only peak behind the curtain was a mention of a very large US customer requesting changes to either the tire or the book, they didn't say which. My guess is DoD and liability/CYA. Your mileage may vary.

As for cab construction, the pictures look like SMC, possibly with an aramid fiber reinforcement but Scott is spot on about the upper mounts becoming moot as the whole upper structure failed as it was not protected. Given the speed and mass involved I'm not all that sure a steel cab would have fared any better without a ROPS in place.
 
#7 ·
#1 - Tire Condition is everything. Old tires at high speed in these vehicles is extremely dangerous. What is interesting to me is the number of discussions I have with customers who will argue this point when comparing costs of new tires against 10-15 year old surplus. Surplus tires have their place, especially trucks that are spending time strictly off-road at low speeds. Putting your set of weather checked 10 year old surplus tires on your truck and going down the freeway at 55-60 MPH should be assessed VERY carefully for numerous reasons.
Thank you for that paragraph, Scott.
I have tried for decades now to convince people that there can be a huge difference between "new" and "never used" tires.
One seller on eBay prominently pointed out that the tires he was selling were new. When I asked about the year of manufacture I was told "around 2008". So in real life those tires were about nine years old already.
I would not want to have that kind of liability, but apparently some people don't mind. Or just don't know better.
 
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