View Poll Results: Do you support more testing of timber cribbing?

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  • Yes, lets get some more data!

    12 80.00%
  • No, I'll use published figures regardless.

    3 20.00%
  1. #1
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    Post Timber Cribbing Revisited!!!

    I realize there has been great debate regarding the topic of timber cribbing. Likely there will be continued debate as well.

    I've reviewed the results of timber cribbing tests performed by the Branch Corporation which are posted on the company's website. It is important to realize that the results are limited to minimal testing, however TESTING was performed.

    Also, I've reviewed the published information available from FEMA regarding timber cribbing, specifically the capacities.

    Indulge me with the math calculations, however without great detail lets take a look...

    The published (FEMA document) capacity for a 4"x4" (2x2 configuration) box crib is 24,000 pounds (12 tons), 6,000 pounds per contact point. That figure reportedly includes a 2:1 safety factor.

    The TESTED capacity (Branch Corp. website results) of Southern Yellow Pine (2x2 configuration) is 20,000 pounds (10 tons), 4,000 pounds per contact point. This figure includes a calculated 2:1 safety factor which differs from the results posted on the website by 50%. This figure gives a more accurate comparison between the two capacities, both including a 2:1 safety factor.

    Lets take into account the contact points provided in the box crib, the FEMA published figures apparently use full size 4"x4" timbers. The Branch Corp website test results are based upon using 3.5"x3.5" Southern Yellow Pine timbers. This amounts to 15 sq. in. (23.4%) less than full size 4"x4" timbers.

    Lets get to the point...the TESTED capacity of the Southern Yellow Pine box crib is 4,000 pounds (2 tons)or 16.7% less than the FEMA published capacity.

    Another issue...hardwood. Specifically Red Maple as tested by the Branch Corp., again in a 2x2 configuration.

    The TESTED capacity of Red Maple (calculated inclusive of a 2:1 safety factor) is 63,000 pounds (31.5 tons), 15,750 pounds per contact point. The size of the Red Maple timbers apparently was full dimensional (4"x4").

    Of greater importance, the TESTED capacity of the Red Maple timber box crib is 43,000 pounds (21.5 tons)or 68.3% greater than the TESTED capacity of Southern Yellow Pine, both inclusive of a 2:1 safety factor.

    By no means is this any support or disdain for any person, product, or orgaization. It is simply an elementary comparison of timber cribbing using FEMA published figures and those posted on the Branch Corporation's website.

    Frankly, I discern the need for additional testing. According to a study published by FEMA, cribbing is the most frequently used extrication tool. Our lives depend on a simple piece of wood to protect us. Lets get some more data.

  2. #2
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    I agree there needs to be more testing, but AS IMPORTANT, the testing needs to be consistent so that an informed consumer can make decisions based on apples-to-apples information.

    The tests between companies all appear to be conducted in a different way. Like I've said before, I think PSI as a measurement is one way of reliably conveying the strength of cribbing. And like some pro-plastic people have already pointed out, strength (off the shelf) is only one aspect to look at when you are considering what to use/buy. I agree.
    Last edited by Resq14; 12-17-2003 at 11:29 PM.
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    Thumbs up

    I strongly agree, testing should be done in a legitimate and consistent manner. There are some other published figures, primarily in engineering books.

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    Southern Pine or Douglas Fir are the only woods that should be used for shoring / cribbing. Hardwoods and the plastic cribbing give no warning prior to failure and often that failure is explosive in nature and complete.
    Any natural product is going to have slightly different capacities.
    It all depends on what is being shored. Cars and even trucks can be shored by wood cribbing.
    Follow all the shoring and cribbing safety practices and you won't have a problem. If you have to your box crib can be 3 X 3 for added strength or even solid for more yet.
    I have seen the plastic slide when it is wet and I have also seen it fail under a load that wood holds.
    For real unique rescues, Heavy equipment, you may need to get creative. Say you have a construction piece that weighs 35 tons. That is 70,000 lbs. When do you not have some of the machine on the ground. Unless you can show me a case study I have yet to see a situation where the entire weight needs to be lifted. Using close cribbing will hold the load.

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    Are you basing your opinion upon actual testing, regarding the failure of hardwood vs. softwood?

    Reiterating, I feel testing is needed.

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    Arrow

    Wood fracturing (failure) is based upon loading and the elasticity of the timber. Info. is available concerning the figure of elasticity. The greater that figure, the greater the 'warning' prior to failure. The fibers will stretch and provide 'sounds' of cracking, thus a 'warning'.

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    I support proper and uniform testing of cribbing.

    At the same time, the results need to be written in such a way that the "average" person can understand them!
    Luke

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    Question

    Originally posted by ADSNWFLD
    Southern Pine or Douglas Fir are the only woods that should be used for shoring / cribbing. Hardwoods and the plastic cribbing give no warning prior to failure and often that failure is explosive in nature and complete.
    Just as there are several types and grades of wood cribbing in use (softwoods, hardwoods, pressure treated, coated, etc.), there are at least four different producers of plastic cribbing. For the benefit of all rescuers, blanket statements reporting product failure should be accompanied by some details so that we all may benefit from this valuable knowledge and we are not left to guess "what failed, and how?"

    While I distribute two different brands of plastic cribbing, the basic raw material of each is the same; recycled HDPE (high density polyethylene). In evaluating the product prior to investing my own hard earned dollars in it, we intentionally attemped to cause failure. With effort, we were successful in causing failure, but only after trying some things that we all agreed we would not do in a "real world" situation. However, I've never observed HDPE cribbing failure that is "explosive in nature and complete." Since plastic will deform under pressure (in essence, the definition of a plastic material), that deformation (change) is our warning prior to failure. Just as "sounding" is said to be a warning with hardwoods.

    As in all cribbing operations, NO MATTER WHICH MATERIAL WE ARE MOST COMFORTABLE WITH, we should be using "spotters" to alert us to potential problems; prior to failure.

    Lutan1:
    You have my vote for "proper and uniform testing of cribbing."
    Last edited by EEResQ; 12-19-2003 at 10:49 PM.

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    I wish I could find the video that I saw several years ago.
    It showed cribbing testing using hardwood, plastic and softer woods. It showed the failure of several different cribs.

    We are probably splitting hairs here since the capacities are relativly close (compared to the total weight) for the three products. What the video did show was how the crib was built was the biggest factor in its performance.

    If the crib is built with the wood back from the edge at liest 1/2 the thickness the crib will be less likely to fail catastrophically

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    Default Plastic deformation

    I agree, plastic deforms (bends) prior to failure. I've used the product and have seen this take place, however no failures.

    Regardless of the cribbing piece used, there are dramatic differences in capacities. There are many variables within these capacities, too numerous to mention.

    I strongly support the uniform and legitimate testing and reporting of capacities. We rely on these simple pieces to protect us as we work. Is anyone aware of an injury produced by cribbing failure? If so, lets hear about it. Anyone with videos to share?

    Regarding the placement of pieces, the pieces should be placed 1x the dimension of the piece from the end. Simply, a 4"x4" piece would have a 4" 'overlap'.

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    Now Billy,don't be giving out all the trade secrets;we'll never get them to the show.When working around heavy equipment,redundency is a key;if one crib gets compromised the second(safety)will buy you escape time or maintain load configuration long enough to effect the rescue.Testing is a valuable tool but variables will always exist in wood density,sinew,age,manufacturer etc.While this is all very valuable to have might I suggest attending a training session;two days that will explore and utilize alternative methods of cribbing/stabilization.The course?Big rig rescue!BTDT got the T-shirt!(not really but I did get a cool patch)I don't often get really enthused but this program is a "Must have" in my book.Very reasonably priced for the knowledge gained.If you're serious about vehicle rescue this is a great place to sharpen your skills.Try it you'll love it.T.C.

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    Thumbs up More methods...

    Youre right Tim. There are additional methods to stabilize using timbers, such as beam support for loaded mixers and tankers. This method lends itself well to 'rounded' surfaces when used with wedges and other means. Ideally it allows rescuers to remain in a "safer" area when constructing.

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    Through an ironic twist of fate, I may have the opportunity within the next few months, to design protocols for and then supervise testing of various types of cribbing materials; all types of wood and the various designs of plastic cribbing. I need your help.

    If you were going to test cribbing materials and could start from scratch to design the tests, what would you do?

    To test material strengths in box cribbing formations, should we just do the crush testing like Frank Maltese did on his Branch Corp. website. Crush until something fails. Should we straight down load onto the entire box crib, and also do off-set load, and point load like when a narrow object is contacting the box crib?

    What about loading a piece of box cribbing that isn't supported by wood directly underneath it? Such would be the case when a solid layer is built as the top layer of a box crib supporting an air bag lifting tool.

    What about capacity testing of step chocks; both homemade wood and plastic? How should they be tested?

    What about those ResQ-Tek step chocks that have the separate sliding piece?

    What about those big truck plastic-type step chocks? How should they be load tested?

    To be realistic, should cribbing materials also be exposed to different environmental conditions; i.e. cold temperature, extreme heat, battery acid, grease and oils, gasoline and diesel, etc? I think those simulations would be realistic and appropriate for real-world applications.

    Any help out there? Any suggestions?
    Ron Moore, Forum Moderator
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  14. #14
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    Ron-

    Yes, to all of the above!!
    Luke

  15. #15
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    Default I agree with Lutan

    I think destructive testing would be the most useful.

    I would take measurements at various weights to record such things as deflection, sounding, cracking, etc.

    The real-world tests involving only the area of cribbing that will be load-bearing makes the most sense to me... such as testing 16 square inches of each type, or something to that effect. To me, full-length loading isn't as important to have information on. Sure, you could do it consistently with all the products, but let's have results that apply to what we do. The box crib tests similar to Cribpac's are what I'm thinking.

    Adding in the variables of environment and contaminants would be very interesting. I'd also be interested in testing of older products to also investigate age. I realize that's not an easy thing to reliably gauge across test groups though... perhaps more of an added-info test.

    I'm not sure what test would be valuable for stepchocks.
    Last edited by Resq14; 12-28-2003 at 05:41 PM.
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  16. #16
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    Lightbulb "PERFORMANCE BASED" Test Cribbing In Ways That We Use It.

    A while back, one of the more sage contributors here stated:
    "Perspective -- Let's remember that a Ford Expedition weighs..."

    As rescuers, if it involves a trapped victim we crib up everything from an overturned 750 pound ATV to a 120,000 pound loaded coal truck. (Yes, DOT has extended weight limits for coal trucks in certain areas of our state - KY.) Does that mean that all cribbing materials carried on rigs must be capable of supporting a 120,000 pound load? "Just how would you stabilize an overturned fully loaded coal truck?" is one of those teachers questions designed to get students to think. I recall that one of the more thought provoking responses to this question came from an old coal truck jockey in the class who responded: "When a loaded coal bucket goes over, they just sort of self-stabilize right where they stop -- it's got that gravity thing goin for it ya know."

    How do we test cribbing?

    First we need to determine how we use it correctly. How do we expect the cribbing to perform? Then we develop test that are relative to that expected performance.

    As stated earlier:
    You have my vote for "proper and uniform testing of cribbing."
    Borrowing a line from educators, "let's push for performance based testing; test it how we use it!"
    Last edited by EEResQ; 12-29-2003 at 05:37 PM.

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    Thumbs up Testing!

    I strongly agree that uniform and legitimate tesing be performed. Of primary importance is that the testing be performed and certified by a registered professional engineer, who should witness the testing and offer expert assistance. Actual tesing is needed to validate, perhaps offer new insight into published figures.

    I think all methods of testing should be performed to gather lots of data. Point loading on 1, 2, 3, and 4 contacts should be assessed, along with loading atypically.

    The testing should be performed using full dimensional wood of highest quality to achieve best results. There is a myraid of methods for actual loading which should be explored.

    The results should be averaged from multiple tests to achieve a common denominator, however I'm uncertain if folks will universally accept the figures.

    Its time for testing!
    Developer and Sr. Presenter, Team Xtreme
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    Default "Best" wood?

    Perhaps the testing should be done in two phases;one with the BEST cribbing you can get and one with a lesser grade which is probably what most Depts have.This would give you "true"and then nominal loading factors.As with chain or lifting straps your "system"is only as good as the weakest part.T.C.

  19. #19
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    Why do we have ratings for chains and not for dunnage?

    The simple answer is...usually when a chain fails, there's a big gap somethings gonna close. Lifting this is especially true. It's true to a usually less dangerous extent when doing pulls of things that could spring back.

    Crib stack starts to fail...it does what? Turn to powder right away? Probably not -- more like compress more. So a member fails, the load drops 4" maybe? Dangerous, sure, but less so than 6" or more lift with a chain that has nothing else below to stop or catch it. Multiple crib stacks should hopefully hold the load and keep a dominoe effect of one thing going bad sending everything down.

    Even at the 80,000# (max in CT with very rare exceptions), the dunnage we carry in our Rescue ain't gonna be enough to provide enough support points. The soon-to-be-in-service Sheeting & Shoring trailer will get special called -- the AirShores for it are in the back of the station as I type. AFAIK it'll also contain an selection of 4x4 and 6x6 lumber, as well as plywood which could be field-resized into ground pads.

    I'm also more concerned when using 4x4 and 6x6 beams as shoring/braces. Unlike a crib stack where the load is mostly under compression, I can see those getting lateral forces more that could knock them lose or put them under a twisting type of tension. And something under tension that fails is more likely I would think to fail catastophically than something being compressed.

    Stabilizing these big rigs is/will be a challenge for us. While our dunnage may not be "strong" enough to stabilize a precarious TT combination, at the same time we don't have enough of it to do the job anyway. Some combination of m/a for more along with chains, winches, and straps would be needed, and when you add all those points together the strength issue is less.

  20. #20
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    Default Talking about cribbing....

    Interesting cribbing in this photostory....

    Conneticut Firefighters Handle Car On Roof

    My training says that you should only go as high as the length of the cribbing used?
    Luke

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    Thumbs up

    Testing will be important, however it must be consistent and the results accepted by all. Presently the FEMA published figures seem to be the most widely accepted. Its time for definitive testing.

    I feel that testing using full dimensional #1 grade wood timber, loading it on all 4 contact points is the basic test performed. That would provide objective results. Testing older, used, or contaminated pieces offers subjective data that may not be useful.

    Tesing to visible cracking and sounding and reducing this figure by 50% (2:1 safety factor) would provide the results we desire.

    Certainly there is a school of engineering and someone who needs a project that could offer us needed data.

    Stepchock testing? A vertical load on each step, to failure. Will be many variables, however an estimation is obtained.
    Developer and Sr. Presenter, Team Xtreme
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