Forums: Skydiving: Safety and Training:
Falling out of a Harness

 

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LeeroyJenkins  (D License)

May 24, 2018, 8:37 AM
Post #126 of 131 (925 views)
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Re: [fcajump] Falling out of a Harness [In reply to] Can't Post

fcajump wrote:
Maybe its time for a rethink from the mfg's on the construction of the chest strap...

It wouldn't be hard to design it as load bearing for such a formation. Chest rings make that easier for this design/intent/use change.

Fail-safe routing design of the webbing at the main lift web would be an easy change from the old sandwich design. With that, I'd guess that the weak point is the PS70101-1 friction adapter (or its 1" little brother) . But if people are willing to have the heavier PS22019-1, that weak link could be removed from the picture (not sure if there is a 1" heavy duty).


I'd be curious to have the mfg's chime in here to discuss their current chest strap options and their strength to handle a second jumper hanging from it during say an inadvertant deployment... (worst? case scenario?)

Anyone?
JW

Bill Booth talks about chest straps in his latest PIA talk. He mentioned that chest straps don't need to be load bearing but since people like to hang shit from they are extremely overbuild and weight bearing. I cant remember the value but it was a significant number.


mark  (D 6108)

May 24, 2018, 8:47 AM
Post #127 of 131 (923 views)
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Re: [fcajump] Falling out of a Harness [In reply to] Can't Post

fcajump wrote:
Maybe its time for a rethink from the mfg's on the construction of the chest strap...

It wouldn't be hard to design it as load bearing for such a formation. Chest rings make that easier for this design/intent/use change.

Fail-safe routing design of the webbing at the main lift web would be an easy change from the old sandwich design. With that, I'd guess that the weak point is the PS70101-1 friction adapter (or its 1" little brother) . But if people are willing to have the heavier PS22019-1, that weak link could be removed from the picture (not sure if there is a 1" heavy duty).


I'd be curious to have the mfg's chime in here to discuss their current chest strap options and their strength to handle a second jumper hanging from it during say an inadvertant deployment... (worst? case scenario?)

Anyone?
JW

The weak link in the hanger in a hybrid formation is not the 500-pound 70101-1 friction adapter. It is the hanger's shoulder, which is not designed for a 500-pound extension shock load.

-Mark


pchapman  (D 1014)

May 24, 2018, 10:32 AM
Post #128 of 131 (865 views)
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Re: Falling out of a Harness [In reply to] Can't Post

(For no-one in particular:)

The standard chest adapter, the PS70101-1, is often looked down on because the only strength usually listed relative to it is 500 lbs. Unlike leg strap hardware which often is stated as 2500 lbs or something.

The numbers are important but a little deceptive on their own. Leg hardware is much heavier, but the numbers above apply to different things.

Leg hardware, much of it is proof tested to 2500 lbs and has an ultimate strength of 4000 lbs minimum.

And even the chest strap hardware actually has an ultimate strength of 4000 lbs minimum, being subject to the same MIL or PIA specs.

At the ultimate strength an item can have bent and deformed but not break. It is toast for reuse, but has held together. (A secondary effect of deforming might be to change the loading pattern on attached webbing, so it is still a bad situation, but the hardware hasn't actually broken apart.)

I long wondered what the actual strength of the chest strap adapters was, and had only ever heard that 500 lbs proof load, which is something which must be achieved without damage.

So I contacted Bourdon Forge, which makes such stuff. I got an email back from their VP of Engineering, Cas Manczuk, and he confirmed that that PS70101-1 adapter has to meet the same 4000 lb minimum ultimate strength as other adapters do under the original MILSPECS.

I think this puts a different light on 20+ years of debate that I've seen about how wimpy and non-load bearing chest strap hardware is.

This doesn't say anything about the harness design any particular company uses for their chest strap, or how the harness and stitching is loaded in non-normal ways when doing hybrids or Mr. Bills. But it does make me feel a little bit better about chest hardware compared to the numbers usually seen.


(This post was edited by pchapman on May 24, 2018, 10:34 AM)


fcajump  (D 15598)

May 24, 2018, 10:44 AM
Post #129 of 131 (847 views)
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Re: [pchapman] Falling out of a Harness [In reply to] Can't Post

Thanks for that.

To continue additional related threads:
If memory serves, the "-1" was added to the PS70101, when the original spec was updated to deal with sharp edges in the stamping process that could cut the webbing.

Thread 1 - With that in mind, I'd be curious if the PS70101-1 would deform enough to pop the slid out before or after the sheer strength of the webbing as it goes around the (relatively) thin metal... (anyone have the equipment to test this?)

Thread 2 - Is the 1" version of the PS70101-1 is a MIL/PIA spec? What is its proof tested load? Especially important since I'm guessing this is more common than the Mil Spec'ed PS70101-1.

JW


jerolim  (F License)

May 25, 2018, 4:22 AM
Post #130 of 131 (649 views)
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Re: [fcajump] Falling out of a Harness [In reply to] Can't Post

 
Quote:
Fail-safe routing design of the webbing at the main lift web would be an easy change from the old sandwich design. With that, I'd guess that the weak point is the PS70101-1 friction adapter (or its 1" little brother) . But if people are willing to have the heavier PS22019-1, that weak link could be removed from the picture (not sure if there is a 1" heavy duty).

Problem with heavier PS22019-1 (or similar) friction adapter is that in case of loose chest strap it can hit you in your mouth on opening, depending of how far it is from MLW and how loose fit is on a jumper. And dental services are not so cheap this days ;)

Also, weight of PS22019-1 would give overall bad hanging look of chest strap.

I think we need something that is not invented yet here ,...


(This post was edited by jerolim on May 25, 2018, 4:36 AM)


drdm

May 25, 2018, 8:37 AM
Post #131 of 131 (595 views)
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Re: [jerolim] Falling out of a Harness [In reply to] Can't Post

Quote:
I think we need something that is not invented yet here ,...

Not necessarily. There are some exceedingly lightweight climbing harnesses out there with very carefully engineered waist strap buckles that need to be rated to more than 15kn to meet CE norms. It would be somewhat harder than a standard adapter to quickly loosen after canopy opening, but it doesn't weigh much and can sure as hell bear a load.

I'm actually consistently surprised that I don't see more modern, lightweight climbing harness type tech in harness-container systems. After all, the shock-loading on the leg straps in a big-but-not-unusual climbing fall probably isn't that much different than the opening shock on typical modern parachute equipment. Then again, maybe for something that needs to be as much of a "workhorse" as a normal sport container system, overbuilt is better. Though that still doesn't explain why you don't see it in hike-and-jump BASE rigs...


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