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#187973 - 11/10/09 05:39 PM Re: Seat belt cutter [Re: thseng]
Tjin Offline
Pooh-Bah

Registered: 04/08/02
Posts: 1697
Originally Posted By: thseng
Naturally we'd like the buckle to fail jammed rather than fail open, but why must it be a binary solution set?

How about option 3: Doesn't fail or jam under a survivable crash loading.

To unlatch while under a load may be asking too much for an automotive style pushbutton release, but the "aircraft style" ought to provide more leverage.

Honestly, current automotive safety systems are so much Mickey Mouse. Race cars don't have airbags or belt tensioners. They have a real harness with a real latch. Yes, I know that's "more expensive" but then again, how much do air bags cost these days?


I don't think thatís the issue. The issue is comfort and ease of use. Race style gear just isnít comfortable when driving.

A tip for cutting seatbelt. Cut at a angle, not 90 degree. Not sure how to explain, but when cutting at 90 degree, the belts seems to fold up and get caught in hook/safety type seatbelt cutters. But cutting a seatbelt is fast and easy in a 45 degree angle
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#187999 - 11/10/09 11:23 PM Re: Seat belt cutter [Re: Tjin]
2005RedTJ Offline
Addict

Registered: 01/07/09
Posts: 475
Loc: Birmingham, Alabama
Originally Posted By: PC2K
I don't think thatís the issue. The issue is comfort and ease of use. Race style gear just isnít comfortable when driving.


You said a mouthful. I've ridden in lots of rigs with racing harnesses, they are a pain to put on. But the difference in a rollover is night and day.

But for pavement driving I'll be leaving the regular belts in also when I put harnesses in my Jeep.

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#188001 - 11/10/09 11:44 PM Re: Seat belt cutter [Re: thseng]
ironraven Offline
Cranky Geek
Carpal Tunnel

Registered: 09/08/05
Posts: 4642
Loc: Vermont
Originally Posted By: thseng
WHY in the world is seatbelt jamming such a common problem?


Fail SAFE.

If you can cut yourself away, you are aware enough of your enviroment to perform a primary assessment of your injuries, the location and stability of the vehicle, and can make some reasonable fine motor motions. On the other hand, if you are knocked out by banging your head on the window during an accident that includes a roll over, the last thing you want is to have your seatbelt release on you, letting you get tossed about. Heck, you wouldn't that if you were concussed, but if my bell has been rung I'd rather be dangling like a pinata than being a lump of rapidly cooling spare parts. (There is very little of Vermont that is flat, if you leave the road there is a very real chance you are suddenly going down hill in an axis of travel other than the designers hoped.)

Never mind that if it the seat belt releases under a shock load of a couple of tons, you've just left the windshield during a 40mph collision.

I want that sucker to jam up good and tight
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-IronRaven

When a man dare not speak without malice for fear of giving insult, that is when truth starts to die. Truth is the truest freedom.

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#188012 - 11/11/09 02:05 AM Re: Seat belt cutter [Re: ironraven]
thseng Offline
Old Hand

Registered: 03/24/06
Posts: 899
Loc: NW NJ
Sorry, I just don't think it's rocket surgery to design a buckle that:

#1 won't fail open at design load
and
#2 will reliably release after being subject to design load

_________________________
- Tom S.
Mora Knives & Adventurer Series Survival Gear

"Never trust and engineer who doesn't carry a pocketknife."

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#188016 - 11/11/09 02:20 AM Re: Seat belt cutter [Re: thseng]
scafool Offline
Pooh-Bah

Registered: 12/18/08
Posts: 1534
Loc: Muskoka
What I have heard a few times was the location of the buckle was a problem. It was easier to cut the seatbelt than it was to get past the person and shift them enough to reach the buckle.
I have been told the problem is worse with "Large" people because they are harder to reach around when they are in a car.
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#188017 - 11/11/09 02:42 AM Re: Seat belt cutter [Re: thseng]
ironraven Offline
Cranky Geek
Carpal Tunnel

Registered: 09/08/05
Posts: 4642
Loc: Vermont
I wouldn't be so sure.

Besides, you left out three further parameters:
1, instinctive understanding of mechanism
2, positive function after potentially tens of thousands of usages
3, cheap
_________________________
-IronRaven

When a man dare not speak without malice for fear of giving insult, that is when truth starts to die. Truth is the truest freedom.

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#188034 - 11/11/09 08:11 AM Re: Seat belt cutter [Re: thseng]
MostlyHarmless Offline
Old Hand

Registered: 06/03/09
Posts: 982
Loc: Norway
Originally Posted By: thseng

Honestly, current automotive safety systems are so much Mickey Mouse. Race cars don't have airbags or belt tensioners. They have a real harness with a real latch. Yes, I know that's "more expensive" but then again, how much do air bags cost these days?


You left out the roll cage... There is welded a virtually indestructible cage of steel around the volume which the driver + map reader occupies. With that kind of protection + the real harness you don't need air bags. (And the way these guys drive, there is a very real risk that the air bag could be set off during hard landings).

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#188118 - 11/12/09 11:25 AM Re: Seat belt cutter [Re: Roarmeister]
MartinFocazio Offline

Pooh-Bah

Registered: 01/21/03
Posts: 2148
Loc: Bucks County PA
I'd like to cover a few issues in this thread.

First of all, like some of the other folks here who were/are first responders, we prefer crashes with people in seatbelts, because that usually means extrication, not recovery.

To address some other points:

Jamming: seatbelts come in a range of engineering concepts, all share some sort of intertial sensing that locks the belt on impact (it's a pawl on a ratchet sort of assembly) and the force of impact can cause deformation in the structure of the belt latch, so that's why they sometimes jam.

Airbag seatbelts: all airbag systems deflate moments after deployment. in the case of the ford seatbelt airbags, the same concept applies. the entire belt is not an airbag, so there are cut points for ordinary tools (I used Medic shears almost exclusively to cut seatbelts on extrications. Medic shears are advanced alien technology).

Fixed (racing) vs. adjustable: a 5+ point harness is a great thing - IF you are a baby in a car seat, with your own personal roll cage. For normal adult drivers, the 3 point harness method is the only realistic method when you have no idea of size and shape of the people who will be driving a vehicle.

Finally...very few crashes result in fire, and not that many crashes are into water. I don't suggest NOT being able to self-extricate from a stuck belt, but it's not a scenario that is all that common. A Res-q-me tool or a lifehammer is a perfectly good tool - don't hang it from your rear-view mirror (I see that a LOT)if you intend to actually be able to find it after a wreck. It needs to be affixed somewhere in the vehicle.

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#188135 - 11/12/09 05:47 PM Re: Seat belt cutter [Re: thseng]
NobodySpecial Offline
Member

Registered: 03/03/09
Posts: 197
Originally Posted By: thseng
design a buckle that:
#1 won't fail open at design load
and
#2 will reliably release after being subject to design load

They all do that, the question is when one is subjected to more than the design load would you prefer it to fail open or fail closed?

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#188140 - 11/12/09 06:47 PM Re: Seat belt cutter [Re: NobodySpecial]
thseng Offline
Old Hand

Registered: 03/24/06
Posts: 899
Loc: NW NJ
Originally Posted By: NobodySpecial
They all do that, the question is when one is subjected to more than the design load would you prefer it to fail open or fail closed?

It is going to fail open when you exceed the tensile strength of the webbing, regardless.

So strike "design load", and insert "webbing tensile strength"

Now can I get a properly designed buckle?
_________________________
- Tom S.
Mora Knives & Adventurer Series Survival Gear

"Never trust and engineer who doesn't carry a pocketknife."

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