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Title: Belts and Harnesses
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drscope
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Posts: 3489
From: USA
Registered: 07/24/2008
Time spent: 51553 hours

(Date Posted:05/29/2014 5:35 PM)
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Belts and Harnesses

 

The expected restraining function of any seat belt or racing harness can only be achieved by optimized strap routing around and from the wearer’s body as well as optimized anchor point locations.

 

An occupant can be effectively restrained ONLY by load transfer through the hard points of the occupant’s body. The only accessible hard points are the following:

 

Pelvic

 

Thorax [chest] to a limited level only

 

Clavicle [shoulders]

 

Therefore, it is essential that strap routing be optimized and mounting points be in the correct location to keep the straps in place.

 

WHAT HAPPENS DURING A FRONTAL IMPACT

 

This data is based on an optimized installation with an upright seating position during dynamic testing. It  simulates a 90° head on collision, utilizing a165 lb mass dummy, an impact velocity of 30 mph and a stopping distance of approximately 16 inches.  Giving a maximum deceleration of 30 G’s.

 

The pelvic load, is expected to surpass 3,100 lb at each side.  This will elongate the lap belt and compress the tissue on the pelvis. The pelvis will slide forward by 3”-4”.

 

The upper torso load is expected to surpass 1,550 lb on each strap.  This will elongate the shoulder belts.  The upper body will roll in, and the adjusters will move up the chest by approximately 8”.

 

Forward head trajectory will be up to  16”.

 

The pelvic movement combined with the shoulder belt forceswill load the anti-sub straps to more than 1,320 lb each in a 5- or 6-pointracing harness and can be intentionally higher in a F-type model where theanti-sub straps are routed rearwards.

 

In more reclined seating positions, the pelvic load will be reduced to approximately 2,000 lb since the seat pan, designed as a ramp, will take some of the load.

 

Therefore it is essential the seat pan is strong enough not to bend or even collapse under extreme loads.  In any case, seats are a significant component of the safety system!

 

 

Lets go back and look at those numbers on the lap belt.  In a 30mph impact with a 165 pound driver,the pelvic load on the lap belt is expected to surpass 3,100 pounds on EACH side!  That’s a total of 6,200 pounds of pressure being put on the pelvic area of your body.  And this is with a PROPERLY fitted and mounted 5 or 6 point harness!

 

If that lap belt is allowed to ride up off of the pelvic area, your internal organs are going to take the blunt of that 6,200 pound impact.  They can NOT withstand that sort of punishment!

 

This is why properly fitted and mounted belts are so important!  And it is also why that 5thor 6th point crotch strap is so important!

 

And the load on that anti-sub crotch strap is going to exceed 1,320 pounds of force simply trying to keep the lap belt in place.

 

Even with a properly fitted and mounted harness, the shoulder straps are going to elongate enough that your head is going to move forward by16 inches.  This is NOT a defect in the design of the belts!  In fact it is part of the safety features built into the belts! That stretching of the belts helps to take some of that deceleration load off the upper body.  By manufacturing the straps out of materials that allow some stretching in the event of an impact,that 1,550 pound load being put on EACH of the shoulder straps allows the body to decelerate a little slower and with less force.

 

Lets just go back and look at these numbers one more time.

6,200 pounds on the lap belt.  3,100 pounds on the shoulder straps.  And 1,320 pounds on the sub strap.  That’s a total force of 10,720 pounds in a30mph impact on your 5 point harness!

 

Those numbers should point out the importance of the harness being properly and securely fastened to the chassis.  If any one of those straps is allowed to move out of place on your body, the loads going into the soft tissue will be far higher then your body can withstand.

 

One common mistake in shoulder belt routing is to have the mounting point too low below the shoulders. This causes the belts to go up over the shoulders and then down to their mounting point. 

 

This compresses the spine of the occupant and because of the extra length of the belts can allow that occupant to pendulum from side to side.  So the driver will fall over to the side in place of staying centered and secure in the seat.

 

If the driver is allowed to move side to side in the seat they run the risk of taking much of the loads being put on the belts by contacting hard surfaces in the cockpit of the vehicle. That 3,100 pound load on the shoulder straps can easily become a 3,100pound blow to the side of the head if the driver is allowed to pendulum out of place.

 

Your helmet, and more importantly your brain can not withstand that sort of force to the head.

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drscope
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Rank:none
Score:3489
Posts:3489
From: USA
Registered:07/24/2008
Time spent: 51553 hours

Re:Belts and Harnesses
(Date Posted:06/12/2014 8:03 AM)

 

While this posting is aimed mainly at one of the newer cars being raced and it’s driver, it also applies to some of the cars that have been running for a while.

 

In previous posts, we pointed out the importance of proper mounting of a 5 point harness.  But some folks either didn’t see that post, don’t understand the importance, or simply choose to ignore the information.

 

Once again we need to point out that having safety equipment isn’t enough.  It needs to be used PROPERLY and if it isn’t used properly, that equipment can cause severe injury in itself!

 

In this case, I feel it necessary to draw attention to a specific car.  Recently on the DRAGG FB page, there were photos posted of Wabbit’s car. This is a green car with a wheel barrow bucket as a seat.  The post contained photos of the car now modified and ready to meet the new DRAGG rules that were put in place following the big crash that severely injured two of their drivers in May 2014.

 

One potentially DEADLY problem is very evident to me from those photos.  And it’s a very simple and easy thing to fix.  Surprisingly I was able to post the problem along with the simple solution on the DRAGG FB page, however in less then an hour my comments were deleted.

 

DEADLY problem - simple fix, and the solution was deleted so it could not be shared with every racer involved, or other racers thinking about becoming involved.  That type of attitude is going to injure, cripple and kill racers involved in this sport!

 

So, if you are reading this, I would once again like to point out, we don’t believe in complaining unless we offer a solution.  So, one part of the solution of closed,dictator type running of the group and a failure to share information, was to start this section of the message boards in order to try to get IMPORTANT safety information to the people involved.  We don’t want to see additional racers suffering pain and injury if those things can be avoided by a free flow of information!

 

The other part of this is pointing out the potentially fatal flaws with Wabbit’s car in the hope’s that HE will see this, and be able to better protect himself from understanding what the dangers are.  And if you have contact with Wabbit, we encourage you to send him to this post so he can get this information for his own good!

 

Every racer needs to look at this and then take a look at their own car and hopefully some of you can make improvements that will reduce your chance of injury when things go wrong.

 

So, here’s the problem with Wabbit’s car.  The mounting of the shoulder straps is WAY too low below the shoulders.

 

This creates two problems. First because the straps go up from the latch, over the shoulder and then down behind the driver, they are too long. This situation causes severe spinal compression in the event of an impact.

 

Go back and look at the numbers in the previous post.  In an impact the forces being subjected on the body go into the thousands of pounds! The body can’t survive that undamaged if the harness is not able to properly do it’s job.

 

A 3,000 pound spinal compression as a result of improperly mounted belts will result in a driver that will NEVER walk again!

 

The other issue is that when the shoulder straps are that long, they allow the driver to “pendulum” from side to side.  In the case of Wabbit’s car, the forward down bars are in line, or very close to being in line with the driver’s neck.

 

The result of that is that in a side impact, the driver is going to pendulum to the side and the driver’s neck is going to impact the down bars.  The head will try to continue on this path and it is very possible the driver will suffer a broken neck – even in a very slow speed impact.

 

So this is a case where having safety equipment is NOT enough!  It needs to be properly used and properly mounted!

 

The solution is SIMPLE! It’s maybe a 30 minute fix!

 

Put the driver in the car seated in the driving position.  Then simply weld a bar across the main hoop that is 3 inches below the driver’s shoulders. 

 

Mount the shoulder straps to that bar and you eliminate or greatly reduce both the chance of spinal compression and the chance of the driver pendulum into the forward down bars with his neck.

 

Taking into consideration that many of the crashes we do experience often end in an impact that is not going in a straight, forward direction, it would also be in the driver’s best interest to install a head rest at the same time in order to reduce the possibility of whiplash injuries.



(Message edited by drscope On 06/12/2014 8:08 AM)
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Mother Nature is a Mean, Evil Bitch

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