the bridle ripped clean off

[biker117 0]

so how did you get out of that situation?

[Calvin19 0]

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so how did you get out of that situation?

what any skydiver would do. he cut away.

[stitch 0]

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so how did you get out of that situation?

what any skydiver would do. he cut away.

I had some help with that though.

"No cookies for you"- GFD
"I don't think I like the sound of that" ~ MB65
Don't be a "Racer Hater"

[TomAiello 25]

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so how did you get out of that situation?

If you're hanging from the tower structure itself, and relatively uninjured, it's possible to climb back inside and onto the ladder. Otherwise, you're stuck waiting for rescue (either from other jumpers on the load, or more formal rescue from emergency response personnel).

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[biker117 0]

but only if he could get good hold of the object, so he wouldn't fall down? i was just wondering what to do if he didn't find anything on the object to grab. but that's probably not a concern on antennas?

[AndrewKarnowski 0]

bounce up and down in the harness until you break loose!!!!! now THAT would be a cool unpacked jump.

[TomAiello 25]

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I was just wondering what to do if he didn't find anything on the object to grab. but that's probably not a concern on antennas?

Wait for rescue. Either (hopefully) your friends who brought rescue gear to the jump (because we all do that--right?), or guys with flashing lights and helicopters.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[Calvin19 0]

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bounce up and down in the harness until you break loose!!!!! now THAT would be a cool unpacked jump.

thanks man. i realy LOL. who the fuck is useing that acronym? thats fucked up.

[biker117 0]

it must be an enormous shock to fall and then be appruptly stopped by the bridle? i mean physically...

[TomAiello 25]

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it must be an enormous shock to fall and then be appruptly stopped by the bridle? i mean physically...

I'm not aware of any cases of this happening on a BASE jump, but I agree that it would be a tremendous physical shock. I do know of some cases where a similar thing happened on static line jumps from aircraft, but in those cases the jumper would have travelled less distance before stopping (because they were closed container incidents).

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[biker117 0]

it sounded like stitch experienced hanging after the bridle from an object? wonder if he experienced the extreme physical shock.

[Calvin19 0]

well, lets look at it.

bridal max length is 9'
canopy to lines is what? 3'? 4'?
lines are about lets say 17'

we are talking 30' almost here.

speed would be about um, math. i love math.

however, dacron stretches, not a lot, but enough. the tape used in canopies streteches, as well as f111, also not a lot, but enough. the Webbing used in bridals is really not that strong, and it stretches a LOT when loaded to what we are talking about.

it would be like this kid,http://www.fugly.com/videos/2394/bungee23432.html

he is some serious competition to our rope jumping systems, obviously.

but seriously,

I would guess that a 3.5sec vented slider down opening would be comparable to this.

also, I would doubt, seriously, that a bridal would take it.

those bridals are not terribly strong. and to be caught by a bridal would mean your being hung byt only 4 suspension lines on your canopy. A 30' fall can produce some SERIOUS forces. I would know.

[TomAiello 25]

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it sounded like stitch experienced hanging after the bridle from an object?

I do not believe so.

If memory serves, Stitch hung from a tower in a more typical BASE fashion (following an off heading opening and object strike).

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[stitch 0]

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it sounded like stitch experienced hanging after the bridle from an object?

I do not believe so.

If memory serves, Stitch hung from a tower in a more typical BASE fashion (following an off heading opening and object strike).

That would be correct.

"No cookies for you"- GFD
"I don't think I like the sound of that" ~ MB65
Don't be a "Racer Hater"

[Tornolf 0]

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and probably not related the the PC breaking at all..just another observation...
The back up static line didnt seem to have any more length/redundancy than the primary static line.....
Doesnt having two S/Ls the same length effectively double the overal S/L breaking strength ( 160lbs if it was standard breakcord)?

It would double, however it would not be 160lbs. 80lb breakcord looped once will break at 160lbs, best case scenario (no uneven loading on the sides, etc - which is hard to do with the way we tie static lines). Since knots weaken the strength, it's lower. A surgeon's knot weakens it around 40%, which is pretty good. So you end up with 96lb breaking force max with a standard piece of 80lb breakcord tied with a surgeons knot. (80*2)(1-0.40)=96.

So the force in that situation would be 192lb, not 160.

A waddling elephant seal is the cutest thing in the entire world.
-TJ

[Zoter 0]

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80lb breakcord looped once will break at 160lbs

Could you explain that some more..?
Woudlnt a piece of 80Lb breakcord break at its weakest point....where it is single strand and not where it has been knotted and looped aroudn itself for the knot.
On the limited number of S/L's I have done where I can observe the breakcord post jump.. the shear point has never been at the knot...but on the portion looped around the anchor point

Thanks

[AndrewKarnowski 0]

the weakest point is the knot.. since it loses 40% of it strength at that point.

all the ones I've seen break next to the knot...

I'll try and get a pretty little chart out of poynters, that might add well to this conversation.

[Poynters Vol.2 - pg347 - 8.80]

[Pendragon 1]

You're right about the knots... but that assumes that nothing is rubbing against any other part of the break cord.

Quite typically, the cord is tied around something that is relatively abrasive (a slightly rusty iron railing for example), which also fits with Zoter's experience (as also mine)

--
BASE #1182
Muff #3573
PFI #52; UK WSI #13

[Zoter 0]

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Quite typically, the cord is tied around something that is relatively abrasive (a slightly rusty iron railing for example), which also fits with Zoter's experience (as also mine)

Actually my S/L experience has mostly been using breakcord tied on a flat climbing sling.
Please dont quote on my 'experience' when you have no knowledge of it....ta

I'm intrigued then how my breakcord is shearing usually about 2cm from the knot....consistantly
I'll get some pics the next time I can

[Tornolf 0]

See attached pic. Since the loading on the break cord is at a single point, which pulls the break cord taught, the load is spread evenly on both sides of the static line. In this case, T2 and T3 are equal, and breakcord breaks when T2=80lbs. Thereforce, since T1=2T2, the load will break the cord at 2*80= 160lbs. This is the theoretical maximum breaking force on the break cord. Since things such at tie off points and knots weaken it, it will never break this high if rigged properly. In the dozens of static lines I've done and seen, when tieing off to a fabric tie-off, the break cord always breaks at the knot. If it breaks elsewhere, then it means that something caused the cord to break at less than 96lbs of tension (approx).

A waddling elephant seal is the cutest thing in the entire world.
-TJ

[Zoter 0]

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If it breaks elsewhere, then it means that something caused the cord to break at less than 96lbs of tension (approx).

Thanks
I think I'll take advice on how I'm tieing off the breakcord ....as its not the tie off point thats the issue I think..

getting back to my original reply...what are your thoughts on having a primary and secondary breakcord tie...that dont vary in length/redundancy...?

[base689 0]

> I've never heard of this situation happening before and as a rigger/BASE jumper, I would like to know
——————————————————————————————
It happened to me nearly that incident. About this time in 2005. I took my student to our S we use for first timers (also for fun for us ); after all the training, preparation, exit trials, it came the moment for his first BASE jump.
I decided his first BASE had to happen via PCA, so we did.
My student sat calmly (...well...) on the handrail, which highest round horizontal bar is 2"-5 cm diameter, you sit on this, plus there other two round horizontal bars underneath, each of these two are 1"-2.5 cm diameter. His ass/thighs onto upper big bar, with feet on lowest small bar.
Handrail is all gray painted, nice smooth surface.
I had gloves on. I had my right thigh pressed against handrail, with a well balkanced stance.
In my right hand I had the S folded bridle and with two fingers of left hand I was holding the PC.
Vertical of my right hand was OUT of handrail, vertical of my left hand was slightly INSIDE of the handrail.
I intended to exert the pulling force with the S folded bridle in my right hand to open his containr and get line stretch, which I did, once line stretch happened, jumper with his weight simply pulled away the S folded bridle off my right hand, immediately followed by bridle pulling PC off my left hand.
In that split second I felt a strange ripping noise and a sort of hard opening. His jump went on uneventfully (apart form "that" event...) and landing was OK.
To make short a long story.
The pieces of handrail (big round horizontal bar and two small round horizontal bars) are 33 ft - 10 m long, each of them with "handles" sticked into concrete, being each single piece NOT welded together but simply "pressed" against the successive one, with a "broken washer" (with diameter slightly larger than bar itself) in the middle of the two.
My biggest fault NOT to check that exactly where I was standing there was a portion of big round horizontal bar containing one of such "broken washers", with sharp edge pointing up, protruding very slightly off the metal profile.
After line stretch and pulling the S folded bridle off my right hand, PC was pulled off and slided onto big round horizontal bar, with PC mesh getting caught on that protruding edge of broken washer.
Of course, mesh could NOT hold the weight of my student and ripped off, but that simulated a very high load break cord SL jump.
There was a 4" - 10 cm sort of round hole in the mesh. PC has been thrown away.
Lessons learned:
1) while doing PCA jumps, keep EVERYTHING (S folded bridle AND PC) OUTSIDE the vertical of structure
2) check for ANYTHING "not smooth" on the structure we are jumping off and take countermeasures in case exit cannot be performed away from such "uneveness".
As soon as I realized what happened, I got a very "cold shower". Glad jump went uneventfully (apart from my student feeling a very strong pull (and buy a new big PC )).
It was clearly my fault for not checking out every detail carefully; nonetheless, big lesson learned for my future students (also for situations in which I MUST do PCA to my experienced mates).
Hope this helps everyone to avoid THAT situation (bridle and/or PC caught onto structure).

Stay safe out there
Blue Skies and Soft Walls
BASE #689 - base_689AT_NO_123_SPAMyahoo.com

[Tornolf 0]

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Thanks
I think I'll take advice on how I'm tieing off the breakcord ....as its not the tie off point thats the issue I think..

getting back to my original reply...what are your thoughts on having a primary and secondary breakcord tie...that dont vary in length/redundancy...?

warning: math below

Well, if they're both the same length then I wouldn't call the 2nd one "secondary" as both are acting in tandem. Obviously it's much better to have them varying in length in case something causes the first to break when loaded. The main advantage to different lengths is that if something such as a sharp railing cut the break cord prematurely, there's a chance it won't happen to the second one. If they're both the same length, you're trading off for a very small gain in overall breaking strength for no real benefits.

I think there might be some confusion of the physics of multiple break cords though. It would be nearly impossible for 2 pieces of break cord acting in tandem to do something like that. Also, when using redundant breakcord (different lengths), the jumper's momentum will be very similar, although a tiny bit more, after both pieces break when compared to 2 equal pieces.

Note that a bridle made from 1" squareweave has a tensile strength of 1000lbs, 1.5" squareweave is 1500lbs. I'm not sure how much the larkshead and stitching at the pc attachment point (which matters since the larkshead on that end is not loaded during a static line) will weaken the tensile strength, but I doubt it's anywhere over 60%. So my guestimate for the breaking strength of a bridle (which is low imo) is 400lbs. Canopies, as mentioned earlier, have a strength of more than 550lbs. It would take way more than 4 breakcords tied in tandem to cause something else to fail before the breakcord.

This should clear some things up:

Force (F) = ma
Momentum (p) = mv
a = dv/dt
Force = dp/dt (change in momentum with respect to time)

To get some concrete numbers to hopefully make this easier to understand, we'll assume that the jumper's center of mass falls 25 feet before reaching linestretch and beginning to load the static line in a significant manner. He weighs 160 lb (~5lbm - 5 pounds mass)
This means his velocity is 40 feet /sec.
His momentum is 200 ft * lbm / s

WIth 2 breakcords in tandem and in good working order, the breaking strength will be 192 lbf (pounds force, btw 32.2 lbf = 1 lbm). For this to *not* break, dp/dt < 192 lbf:

F = 192 lbf = dp/dt
dp/dt = d (200 ft * lbm / s) / dt = 192lbf
with some simple integration it shows that it would take nearly an entire second of constant momentum change before the static line would not break. So if the cord is loaded for less than 1 second if dp/dt is linear, it will break. I doubt there is any way the loading will be constant, so any spike over 192 lbf will break the cord. When you consider the speeds and distances involved, the breakcord is loaded for a very small amount of time. When discussing "shock force or load", people are mainly talking about the change in momentum with respect to time rather than static force.

In the case of 2 different length break cords, the overall change in momentum will be nearly equal to the previous example. The only reason it's different is due to the small, negligible extra inch or 2 of freefall the jumper gets between the two break cords.

In other words, if 2 break cords of equal lengths would cause someone a hangup, 2 different length of break cords should do the same thing, but the first cord will break and the second will hold the person. Using 2 different lengths of breakcord to try avoid a hangup is ineffective. (math below)

F1 = 96lbf F2=96lbf
dp/dt = d (200 ft * lbm / s) / dt
after breaking the 1st breakcord, dp/dt = d (200 ft * lbm / s) / dt - 96lbf
when loading the second cord, if dp/dt < 96lbf, the second cord won't break.
d (200 ft * lbm / s) / dt - 96lbf = 96lbf
d (200 ft * lbm / s) / dt = 192lbf
it's the same equation as for 2 pieces of static line the same length.

A waddling elephant seal is the cutest thing in the entire world.
-TJ

[n_pertuset 0]

nerd

Nathan

[TomAiello 25]

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In other words, if 2 break cords of equal lengths would cause someone a hangup, 2 different length of break cords should do the same thing, but the first cord will break and the second will hold the person. Using 2 different lengths of breakcord to try avoid a hangup is ineffective.

The purpose of using two different lengths of cord isn't to prevent a hangup, it's to prevent a premature breakage. It essentially gives the break cord, which usually works, a second chance in the event that it fails the first time.

The reason to make the two engage at different times is so that if there is some unusual circumstance that prematurely breaks the first cord, it is no longer taking place when the second one loads.

Without subjecting me to math, can you tell me if this line of reasoning is or isn't supported by your calculations?

-- Tom Aiello

[email protected]
SnakeRiverBASE.com