Since you keyed in on it, any problem with using a backwards thrust block as a coner block in your mind?
The "Corner Bracket" method works best when either corner has caved in. I have only seen an outside corner cave in one time so its usually the inside corner that drops. Any cave in that can be filled with back-fill or an airbag work great with the corner brackets. In fact we always teach this section of the program with a missing corner and an appropriate sized pile on the trench floor at the corner. We have another method for huge corner cave ins that are bigger than rescue air bags. If you are the guy who everybody turns to with a trench problem I'd get signed up for our Trench Rescue Technician class. There is a lot more to designing technician level shoring system than just cramming stuff in the hole. Unfortunately designing "tested" systems is rarely taught correctly.
Not sure if this is the whole thing. It says abstract. Sorry if I didn't link it the right way.
Either way great information. Its nice to see people testing these systems and getting the information out there. Good Job Ron.
I have found the thread very interesting. I have seen the original example actually happen during training. Lucky we had no one hurt, afterwards it was decided that incorrect pressures (diagonal and straight shores shot at same psi) were the problem, exactly as described in earlier post. Ron would it be possible to see more pictures or drawings of your application? Thanks in advance!
I'm sure that I can find some more pictures of the "Corner Bracket" shoring system. Contact me by e-mail to get some. Trouble is I can't teach you how to properly install this on-line.
I looked at some previous threads on your site. There seems to be some very smart people asking some very smart questions. I'm wondering, however, if the answers that are given are based on testing and quantitative data or if they are based on myth and here say. Appears to be more of the latter.
I saw a post asking about the Paratech walers and thrust blocks. I'm a big fan of Paratech but remember that any thrust block system that is installed without resolving the diagonal vectors will fail (like the Rescue 2 video) regardless of the thrust block material (aluminum or wood) composition.
I would agree that much of the information available is based on myth and here say. But I might also spin that alittle towards, in my opinion, different terminology. Namely, past practice.
While the use of ropes has a basis in rock climbing and thus many years of critical research and development. Many USAR disciplines come from "non hobby" applications and thus we are forced to base our methods on information supplied by the military and manufacturers rather that personal experience. I am certain that should my company be dispatched on a trench rescue tomorrow, there will not be a single responder that holds much more knowledge in the subject matter than myself. I find that a scary scenerio as I feel im only "adequately" trained in the subject matter. I know what I was taught but really have no way of verifying the veracity of that information.
We can be shipped all over the country for tech search, SCT, heavy rigging, logistics and all other aspects but little by way of trench is available for absorption.
Does the field of trench rescue need more research on safe, effective, effcient metodology? YES! But it doesnt appear at the moment that it is "glamorous" enough to grab the funding needed to properly address the concern.
You make some very good observations and valid points. In relation to the number of years that rope has been used by the fire/rescue service the destructive testing and data collecting is relatively new. The British Columbia Technical Rescue Team got the ball rolling with drop testing on belay systems only about twenty-five years ago. They started out with a few subject matter experts who paid their own expenses and had no major corporate or government funding. Some equipment was donated by individuals and/or rope equipment manufacturers. We have taken the same route.
I hope to create a video that shows how simple it is to test the strength of trench rescue shoring components and systems. We have had some help from the pneumatic strut manufacturer that we use (Paratech) which replaces any broken parts in exchange for the research and development that we provide at no cost to them. I should point out that the strut equipment (most expensive parts of a shoring system) almost never fails. We also build the cost of replacing some items into the student tuition (which is still pretty reasonable). I believe that the learning that takes place here is unmatched in any other Trench Rescue Technician class. I am hoping that destructive testing and quantitative data collecting will become part other Trench Rescue Technician programs. If we do not do the testing no one will.
I just sent you an email. Thanks for your input on this thread.
I like new ideas to be able to pick which may be applicable to the situation, as we all know not every event is the same or as perfect as they are in a class setting. I'm also not throwing rocks at Ron's idea or test results. As a side note, I skimmed through the test results and I can only say "do you have a firefighter edition"? What a head spinner. My question, Ron talks about test and studies, I agree that applications should be used with proof testing, have saddle and thrust blocks not been tested? The first time I was introduced to using "saddle and thrust blocks" was from a group of instructors that had been working with Airshore/Hurst on this technique. Hurst now sells these "blocks" made out of some type of metal. As many of you know, they can be easily made out of a 6x6. Did Hurst not test this new product and look at the forces appied by the struts on trench walls?
I can not speak for Hurst. My guess is that they have tested the compression strength of there struts but have not tested the system. If they showed you how to set up this system, without resolving the diagonal vectors, I would be more inclined to say that they did not test the system capacity. I say that because Hurst is a reputable manufacturer of fire/rescue products and would not have concealed the results of a system test.
Back before destructive testing was started on rope rescue (systems and equipment) a lot of things were being taught that were incapable of withstanding the potential forces. The equipment and procedures were thought to be safe because they were "used" for years without problems. The truth was that the systems set up and used thousands of times but they were never tested. An example is belay systems. As long as no failure occurred in the main line the belay systems were thought to have worked. The "drop tests" that were conducted by the British Columbia Technical Rescue Team showed the lack of effectiveness of many belay techniques when a standardized force (15 KN) was applied to them. In my opinion trench rescue is in the same position that rope rescue was in prior to standards and destructive testing.
Now for the real head spinner. It seems hard to believe but trench shoring systems being taught in “accredited programs” (IFSAC, ProBoard, Fire Institutes, Strut manufacturers etc.) have never been tested. Out tests have shown that some of them are not capable of withstanding the potential forces of the soil they are installed in. You could install them a hundred times but if the soil never became active they have not been tested. We create forces during our test that would duplicate the forces seen in Type C soil. The forces are measured with load cells and the quantitative data is collected. I am very surprised and disappointed that no other organizations have seen the need to something similar.
I must say that I have really enjoyed reading this thread.
I have personally taken Ron's trench classes (Operations and Technician) and they are worth every penny and every hour. I have also seen some of the testing he does to prove out everything that he teaches. He is the constant student of the trench, always trying to learn a better and safer way to work in the trench.
If you have the chance to take one of the classes offered, JUMP on it. You won't regret it.
Ottawa County Technical Rescue
I have been debating on posting to this thread for a while; I do have a diffrence of opinon and don't want to come across as arguementative as I respect the work being done by our Michigan brothers. You all have made a good name for yourselves up there.
Here we go....I do not agree whole hartedly with the pervious posts about the traditional use of thrust blocks being dangerous. I have personnally used this method with great success for my 15+ years in this industry. We have used it in Southern red clay (which practically needs no shoring), to darn near running material in South Florida, and extrememly sandy soil in Wisconsin. I know this is not empiracle data, as one could say we were lucky; but the point of the matter is there is a right and wrong way to use the thrust block technique so I don't think luck played a factor at all.
Any shoring principle, whether structural collapse or trench, is to transfer loads and only apply enough force to hold back (or upright) the material. No more pressure should be applied than is needed. Where I diasagree with the testing of the thrust block shoring method used by MSU is it appears that they apply a surcharge load (external load to the lip of the trench) to increase wall pressure; thus failing the trench. (Please forgive me if I misread the testing method) I see this as a flaw in the scientific testing method to determine if the shoring technique is safe or unsafe. Obvioulsy, a change in wall pressure (of a certain amount) will affect the compression on the corner struts and conversely the ability of the inside panels to maintain cohesion to the trench wall.
Any trench course you take will harp on minimizing surcharge load. Therefore, this is a very controllable variable during the rescue. With that said, I see no reason to discredit the traditional shoring method. In order to validate this line of thinking, I did discuss the post with one of the larger shoring manufacturers to discuss the concept presented by Trench Dog vs. traditional shoring. They came to the same conclusion and went on to say that, obviously, they have engineers as well that certify the shoring systems. Just a difference in opinion? Possibly. But in our industry we sometimes, myself included) try to creat solutions for problems that either don't exist or solutions to problems that are a training issue and not an equipment issue...I refer back to a previous comment I made...our equipment rarely fails us...we fail our equipment.
The video that started this post is a clear example of rescuers failing their equipment.
Again, I post this difference in opinion with the utmost respect; anytime folks are willing to invest the time, energy and resources to make our industry safer and more efficient they deserve it!
You bring up a case for one of the issues I am trying to address. You and I have a difference of opinions on what is considered safe trench rescue shoring. A guy in Illinois has a third opinion and a firefighter in California has a fourth… etcetera and etcetera. I believe that a national standard for trench rescue shoring system needs to be developed with a minimum load bearing capabilities set forth. This national standard does not have to follow what we are doing in Michigan. It should, however, come from a consensus agreement of trench rescue shoring expert subject matter expert and should be based on quantitative data.
The fact that you have not had a system failure in fifteen years of shoring does little to offer proof that the systems you use are either safe or unsafe. What it likely proves is that the soil that you were shoring did not become active while you were working there. In my experience shoring live trenches (more than 600 times) I have witnessed passive soil become active at both training and real trench operations. A few times this resulte4d in substantial cave in directly adjacent to the panels and in one case it involved creating so much additional force behind the panels that the struts could not be removed by traditional methods.
Several times during the past decade, I have painted a large orange “X” on the wall of a trench that we were training on. I have done this in a variety of soil conditions. At no time did the walls with an orange “X” collapse. One might conclude that orange paint in the shape of an “X” provides adequate resistance to Type B and some Type C soils. My conclusion, on the other hand, is that the soil never became active during the time that we were using it for training. In other words, my “Orange X shoring System” system was really never tested.
In our rope rescue discipline a similar problem existed. A variety of belay techniques were being used to catch a two person load in the event of a main line failure. They ALL worked (for decades with thousands of uses) as long as the main line didn’t fail. It wasn’t until a group of subject matter experts being to actually subject these systems to the forces that a two person load could impose on the system that it was shown (empirically) that many of the belay systems were not capable of “catching” a two person load. They tested this by artificially imposing a load (cutting the main line). We impose an artificial force on the shoring systems that we test as well. Imposing artificial loads during testing is a valid testing procedures as long as the forces are within the range of reality.
OSHA has agreed to accept the lateral force (Type A @ 25 psi, Type B @ 45 psi and Type C @ 60 psi) which have been assigned by the trench shoring manufacturers. In our testing we impose the forces to the types shoring systems that are being used by trench rescuers. We use forces that Type C soil (worst case scenario) could create at the depths that are commonly seen by trench rescuers. These are not forces that we invented. These lateral force exist without the influence of “surcharged” loads. They are forces that OSHA and the shoring manufactures have agreed to.
Tabulated data from the manufacturers of struts is based on the compression strength of the struts. In the video, the struts friction based contact point (distribution point) did not allow the struts to work in compression because it moved. The design of the shoring system (in the video) took the struts out of their tested element (compression) and introduced shear and tension into the system which is why it failed. Asd a result, the system proved to be much weaker than its component.
I’m unaware of any PRE who has ever tested and certified a trench rescue shoring system. If you know of one who has, please provide me with contact information. Furthermore, I don’t know of any PRE or manufacturer who has certified the use of the “thrust block shoring system” as seen in the video. Please, please provide me with that person’s contact information.
You mention some shoring basics. Those should include collect the load, funnel the load and distribute the load. There are three points where the system must have minimum strength that are based on the force the system is designed to resist. What the designer of the system used in the video failed to do was to follow the load to its point of distribution (inside corner). At that point the friction created form the contact between the panel and soil (enhanced by the air pressure from the perpendicular struts) was clearly not capable (shear/tension) of resisting the forces of the air pressure in the diagonal struts. The entire shoring system failed as a result of normal operating air pressures. These are forces that are much, much lower than what OSHA says can be created by lateral soil pressure. This system could not resist the lateral force of Type B or Type C soil.
You also state “Any shoring principle, whether structural collapse or trench, is to transfer loads and only apply enough force to hold back (or upright) the material. No more pressure should be applied than is needed.” I must respectfully disagree with that premise and can provide you with tests and studies which show why struts in trenches should always be pressurized to substantial forces and not just tightened enough to stay in place. Your reference is to a technique that is used in structural collapse and it is uniquely different from trench and excavation shoring. I’ve already taken up too much space in this thread but if you are interested…contact me by e-mail.
The trench rescue shoring systems that we use have been tested to at least twice the lateral forces set forth by OHSA and shoring manufacturers. That gives our systems a proven 2:1 safety factor. I know that the struts we use have a tested compression strength which meets or exceeds that safety factor. I can produce data which supports the fact that our systems provide a minimum standard of safety. I hope that you can do the same for rescuers entering trenches that you have shored.
I really do hope there is no offense taken in my post. You had a few comments that I wasn't sure if were comical satire, or you were getting frustrated.
I will work on getting you the info on the engineers review. Years a go airshore actually had stamped drawings in a field guide. I don't remember if they were only collapse drawings on not. All I can say is both Hurst and Paratech would be hurting if someone was killed using their thrust block equipment in the fashion it was intended.
The active soil part of your test method is where most of my question lies. Yes I have seen soil become active in an open trench and near a panel but how are you making shored wall soil become active in your testing? What real world condition is this simulating? (Where a shored segment becomes active) I'm asking as I have never seen this to the extent you describe of not being able to remove equipment.
I understand that the trench shores need to be pressurized; a little misstep in my analogy. I also am pretty clear on the lack of support by an orange X on the wall. Although one could also argue the orange X did support the wall as you note it never failed. :)
I really would love to go through your documents for this thread and to continue this debate off line. I haven't a clue how the messaging stuff works so please email me at Jeff.firstname.lastname@example.org. If you want to look into standardizing a system I'd love to help. While I'm not drinking the Kool-Aid quite yet; you may be on to something and I have an alternative method I'd like to share and see if you guys have tested. We have used an alternate method within our circle (not in classes), but you have much greater access to practical testing.
Seriously, I think this thread has opened some eyes. Hopefully those in power have caught some of this, at least to address it and figure out if what we are doing is right or not.
I would like to suggest that since we are all capable of having civil dialogue, unlike other threads on this forum, that the discussion be continued here in open forum. I understand if you would prefer otherwise. I just feel that since both of you seem to have a wealth of knowledge and experience, others here could learn from possibly 2 differing opinions.
On a side note, I have yet to bounce the pics I received from you off my bosses heads as they were on a lengthy deployment and when they returned I went on vacation. I return to work tomorrow and hope to speak with some other task force members over the next few days. I will get back to you with some questions and any thoughts raised during these discussions.