Seat Harness Life?

[caverdan]

Seat belts in cars have been required since 1967 or so. I have never heard of them being replaced or being expired and they get used much more then your typical seat harness. Often they are left in direct sunlight, too.

Phil...FWIW.....Seat belts in airplanes have tags on them that give date of manufacture. I'm not up on my FAR's anymore......but I know there is an age limit to seat belts and the maintience inspectors for airlines inspect and track them. I won't say for sure but I wouldn't doubt if the age limit is somewhere between 10 and 20 years. It's also part of a small airplanes annual inspection. Airplanes in general are controlled by the FAA on a national level.......Not sure how you would inforce something like this on car owners?

[ek]

Seat belts in cars have been required since 1967 or so. I have never heard of them being replaced or being expired and they get used much more then your typical seat harness. Often they are left in direct sunlight, too.

But not as often as it might seem, for most users, because glass is extremely effective at filtering out UV light. If you leave the windows open in the summer, then you'll get some UV, but when the radiation peaks, it will be at the wrong angle to penetrate. It seems to me that if you leave the windows open in the winter, that might potentially be a bigger problem, because even though there is less radiant intensity per unit area, it could easily reflect off snow and bounce in (this is the same reason why people often wear sunglasses when hiking, snowshoeing, or skiing on a sunny day.) But nobody leaves their windows open in the winter, so that doesn't really matter.

If you have a vehicle with an open top that cannot be closed, and drive it in the winter, and keep it outside whenever it is parked, then potentially that could be an issue. On the other hand--and this is just a guess!--I think seatbelt webbing is substantially more overstrong than a rope or harness. The amount it gets loaded in a crash is probably a lot less than the maximum possible loading of a caving/climbing harness or rope. Furthermore, it is subjected to a lot less serious abuse--calcite crystals are not being rubbed into it, for instance. And it's not supposed to be taking multiple impacts--my understanding is that you're actually supposed to get your seatbelts replaced (or at least inspected) after a significant crash.

[Tenzin Beck]

It may be worth noting here that most seatbelts are made of kevlar whereas most harnesses are made from nylon. Nylon is typically not known for phenomental UV resistance (though I suspect most harnesses and ropes have degradation inhibitors). I have no idea how resistant kevlar is to ultraviolet radiation.

[sherppa]

It may be worth noting here that most seatbelts are made of kevlar whereas most harnesses are made from nylon. Nylon is typically not known for phenomental UV resistance (though I suspect most harnesses and ropes have degradation inhibitors). I have no idea how resistant kevlar is to ultraviolet radiation.

Nylon is more susceptible to UV and chemical degradation than polyesters and its physical properties can change due to moisture absorption. Kevlar has poor UV resistance and loses strength roughly twice as quickly in sunlight as polyester.

[Billy]

It may be worth noting here that most seatbelts are made of kevlar

Umm, can you back that up? Last I knew, seat belts were absolutely made with nylon or polyester. From my experience working with kevlar lines, it'd make a lousy material (repeated bendings for one thing, one second you have a line, the next it's just like fatigued metal - my opinion).
I think the most hands on person to answer this would be Shibumi, I think he's still putting seatbelt material on his packs. He'd know.

[NZcaver]

It may be worth noting here that most seatbelts are made of kevlar whereas most harnesses are made from nylon. Nylon is typically not known for phenomental UV resistance (though I suspect most harnesses and ropes have degradation inhibitors). I have no idea how resistant kevlar is to ultraviolet radiation.

I agree with the recent comments. I'm not sure you're correct about most seatbelts being made of Kevlar. I'd always assumed the material was still nylon or polyester. I bought seatbelt webbing in bulk years ago to make harnesses and pack straps etc, and that was nylon. I did a quick online search, but couldn't find direct references to kevlar seatbelts. Most are nylon and polyester. Polyester seems to be the more popular material.

As others have said...

The ultraviolet light component of sunlight degrades and decomposes Kevlar, a problem known as UV degradation, and so it is rarely used outdoors without protection against sunlight.

Source wikipedia

[ek]

And as a vendor source, Beal says of its aramid ropes: "Storage in a rope bag essential to protect the rope from light."

[NZcaver]

It may be worth noting here that most seatbelts are made of kevlar whereas most harnesses are made from nylon.

OK, I just found a very interesting article which pretty much debunks that myth. Here's the relevant excerpts:

The first patent for an automotive lap belt was granted in 1907, but it wasn't until 1956 that a major U.S. carmaker offered the device. That year, Ford Motor Co. included front and rear lap belts in its optional Lifeguard Safety Package. Developed by Ford for automotive applications, the belts were two inches wide and constructed of very tightly woven nylon. Nylon was the material of choice because it was affordable, very strong and reasonably flexible.

...In the early '70s, carmakers began replacing nylon with polyester as the belt fabric of choice. No, it wasn't trendy leisure suit polyester—it was a stronger, heavy-duty industrial version, more along the lines of the tie-downs used on flat-bed 18-wheelers. Woven into a two-inch wide belt, it equaled or bettered the strength of nylon but in a lighter, more flexible and more comfortable construction.

...Other researchers are [now] looking beyond varying a seat belt's configuration. They're studying that polyester material. Honeywell International Inc., for example, has developed what it calls a "smart fiber" that stretches in a controlled manner in a car crash. This eases the stress on the occupant in much the same way as the elaborate assembly of mechanical, electronic and even pyrotechnic pretensioners and force limiters carmakers are currently using.

The new fabric, which Honeywell has dubbed "Securus," would allow the elimination of such devices, saving not only costs but providing a better seat belt. "Today's seat belts are actually too strong," said Craig Trask, Honeywell's business manager for Securus, and can, in fact, contribute to fatal injuries "like in the Earnhardt crash."

Source msn autos

I wonder if that guy meant to say "too static" instead of "too strong?" With this current line of thinking, I'd assume seatbelts made of Kevlar would NOT be a good idea. Probably not good to make a seat harness out of it, either.


PS welcome back, Eliah! Long time no hear.

[Tenzin Beck]

Ah, guess I was wrong! Thanks for digging up that citation... now I wonder where my misconception came from in the first place.

[knudeNoggin]

On the old-seat-belts note, as best I can find with a check now
of what I was told some time ago, they're made of polyester,
which of the usual fibres has the best UV resistance. Harnesses,
now, ... nylon?

*kN*

[Bob Thrun]

If you burn the webbing or rope (just melt an end in a flame), is is easy to distinguish between nylon and polyester by the smell. I have some nylon webbing that looks exactly like seat belt webbing. But that does not prove anything. I have some webbing that you could not tell if it is nylon or polyester by looking at it. These are two webbings in different colors, but otherwise identical in appearance. I sent some pieces of the two to ek when we were having a different discussion about webbing materials. Ek, did you ever tell which is which?

[knudeNoggin]

By your sniffer? -- not if you don't have a reference smell.
Or taste? -- "tastes like chicken", nah.

Sighted investigators can tell by smoke color : white if by
nylon, black if by polyester (or PP or PE -- which fibres however
sustain burn away from the flame source). Stick kevlar into
the flame and it ... darkens -- found one bit of (straw-colored)
kevlar cable-hauling tape around the area (all seems to be of
the slippery/lubricated ("Muletape", mostly) polyester sort,
marked per foot, 1800# half-inch width), and gave it a burn.

*kN*

[Cavernuke]

It may be worth noting here that most seatbelts are made of kevlar whereas most harnesses are made from nylon. Nylon is typically not known for phenomental UV resistance (though I suspect most harnesses and ropes have degradation inhibitors). I have no idea how resistant kevlar is to ultraviolet radiation.

Kevlar degrades rapidly from UV exposure. When used for sailboat halyards, the kevlar is generally inside a dacron cover.

[Marlatt]

Several years ago, I took a Boy Scout climbing safety course (which gave me some certification, and insurance coverage by the BSA). At the time, the instructor insisted that the 'official' BSA policy was to replace ALL climbing equipment every year. This included all ropes, slings, harnesses - and all metal gear, including carabiners, belay devices, rappel devices, cams, nuts, etc.

For what it is worth, that isn't the actual BSA policy, at least not now...

swm

[NZcaver]

Several years ago, I took a Boy Scout climbing safety course (which gave me some certification, and insurance coverage by the BSA). At the time, the instructor insisted that the 'official' BSA policy was to replace ALL climbing equipment every year. This included all ropes, slings, harnesses - and all metal gear, including carabiners, belay devices, rappel devices, cams, nuts, etc.

For what it is worth, that isn't the actual BSA policy, at least not now...

I agree. I recommend the BSA forward all retired gear to me for further testing.

I also recommend they adopt a policy of replacing all misinformed instructors every year.