Trench Rescue in Spring Arbor

On Friday October 19, 2012 the Spring Arbor Fire Department (Michigan) was called to the campus of Spring Arbor University for a man trapped in a trench cave in.  Upon arrival, members of Spring Arbor Rescue #1, assessed the scene as one person buried to his chest in trench that was twelve feet deep.  The victim was conscious and trying to dig himself out with the help of his coworkers.  The Spring Arbor Fire Department requested a trench rescue team from the nearby Summit Fire Department.  Summit is a member of the Michigan Regional USAR Response System.

Hearing the call from home was Summit Fire Departments’ Lieutenant Scott Stoker who resides in Spring Arbor.  The off duty Lieutenant recognized that the incident was only a few blocks away and responded from his home.  Upon arrival he noted numerous workers and firefighters in the trench digging the victim out.  Obvious hazards included the extremely unstable soil conditions, exposed utilities and unsupported concrete slabs hanging over the rescue area.  Stoker’s immediate concern was to remove the firefighters and workers from the trench.  After some convincing he was able accomplish that as the victim continued to dig.   Continuing on with site control (Initial Actions) Stoker had a ladder placed into the trench and eliminated vibrations by having all heavy equipment shut down.  Heavy equipment included two excavators which were running at the lip of the trench.

When the members of the Summit Fire Department trench rescue team arrived they placed ground pads and took measurements for primary shoring operations.  At that time the victim freed himself from the collapsed soil.   He had injuries to both legs and was unable to climb the ladder to escape from the trench.   The focus of the tactical operations quickly changed from shoring to non-entry rescue.  Rescuers re-positioned the ladder (already in the trench) so the victim could support his body and hold onto a rung with both hands.  From a safe area on the trench lip (ground pads) rescuers were able to utilize a “moving ladder slide” technique to extricate the victim from the trench.  Within minutes of extricating the patient from the trench a second cave in occurred.

The patient was treated on the scene and transported to Allegiance Hospital in Jackson (Michigan).  He was treated for a fractured lower leg and is expected to return to work following a rehabilitation period.

The Spring Arbor Trench Rescue is a clear example of the” best” of all rescue opportunities (Non-entry Rescue).  The fact that the stage was set for a successful non-entry rescue was a tribute to good training and command presence.  Gaining control of the scene eliminated the potential for additional victims.  Site control (ground pads and stopping vibrations) improved the window of opportunity for rescue by postponing the secondary collapse.

submitted by

Aaron Osburn
Summit Fire Department
MI-TF1

 

Hole Rescue #2

In the “Hole Rescue” part 1 blog I talked about an alternative tactic for lip safety at trench incidents where ground pads can not provide adequate protection.  We call the tactic a Lip Bridge.  The pictures below shows scenes from a trench rescue in Bay City, Michigan. This trench (repair hole) was about 6’ wide, 9’ long and 16’ deep.  Three of the four walls had sloughed creating large overhangs.  More than 15,000 pounds of unsupported soil hung ten feet above the victims head.  Stepping on the lip would have surely caused the overhangs to break off and land on the victim.  Traditional ground pads would have distributed the weight (distributed versus  concentrated loading)  of the rescuers but would have still had the load directly on the overhangs.  Our goal was to transfer  the load away from the overhang areas to solid ground.

Photo #1

We accomplished this goal by creating a bridge system.   The foundations for the bridge were 4×4 cribbing which was set on solid ground about 5’ away from the lip.  The cribs elevate the first bridge (fire service ladders) which span the short walls of the trench.  Other ladders or lumber can be used to span from the short wall bridges at each end of the trench.  The result is that rescuers can install shoring material on all four sides of the trench without ever loading the lip.

 

Note:  At the Pompano rescue I don’t see this type of cave-in pattern (slough-in) however, beach sand is very susceptible to cave-in caused by surcharged loads on the lip.  A lip bridge may have made thing safer.

Photo #2

The patient was a city utility worker with more than 30 years on the job.  When I arrived he was buried to his armpit level with his arms also buried.  This picture shows our initial digging effort which freed his arms and relieved pressure on his chest.  At this point we have him on oxygen with an IV in place.  We had one of our USAR task force Medical Managers (E.R. physicians) on scene and as the incident progressed crush syndrome considerations were examined.

Photo #3


This photo shows the completed shoring system.  “Cross shoring” was needed to protect all four walls.  Giant low pressure airbags from a tow truck company were used to manage the voids created by the slough-ins.   Supplemental shoring was installed as we dug the victim out.  He was standing when the cave-in occurred so we had to dig more than five feet below our initial panels and shores.

Time Frame:
Primary shoring (protect the victim) was completed within 40 minutes of our arrival.  Secondary shoring (completed system) was done in less than two hours.  A vac truck was used to help dig the victom out of the moving/sandy soil.

 

Hole Rescue

What the Pompano Fire deaprtment experienced is what I call a “Hole Rescue”.  It is a unique type of trench rescue.  This one happened to be in sand.  At hole rescues the victim and rescue entry team are in the collapse zone of all four (directions) walls.  This is almost never the case in a trench that has been cut to install utilities which usually has collapse potential from two walls.
In the next post (Hole Rescue #2) I have provided a few pictures and suggestions from one of the “hole rescues” that we have responded to.  Our hole was a little bigger and deeper (16′) than the one in Pompano but it was also in sandy soil.  It occurred a few blocks from the Saginaw River (Michigan) and was river bottom sandy soil that continued to slide as we worked.  If you have a copy of Buddy Martinette’s Trench Rescue: Awareness, Operations, Technician book you can find a “Voice of Experience” section on this rescue with more details.
The basic objectives for an awareness response are: Site control, scene management, activation of the response system, identify/mitigate hazards and perform non-entry rescues.  As a first responder (awareness level) organization it looks like the PBFD did a good job covering these objectives. As is usually the case, I assume that a non-entry rescue was not a possibility.
A concern that I have is taken from the picture of the lifeguards on an unprotected lip. The weight (surcharge) and vibration of the people working on the unprotected lip creates a high likeliness for cave in.  Had an additional cave-in occured it would have reflected poorly on the scene management/site control and could have caused additional injuries to rescuers and the initial victim.  Some of the later pictures show that the lip was protected with surfboard used as ground pads.  I hope that corrective step took place soon after arrival.  As far as problems with site control (zoning) I have found that 42″ steel pickets with barrier tape work well at a trench scene for developing a hot zone.  PD works well for traffic control and establishing a warm zone.
From a shoring design perspective the backboards that were installed by the lifeguards probably offered very little, if any, protection.  The lateral forces on each wall would be between 2,000 and 2,500 pounds.  I’m not sure what the thought was for placing the backboards in the way they are shown, however, it looks like they may have tried to push the boards into the trench floor and utilize a type of sheet piling technique.  When sheet piling is used in sand, a sheet has to be driven into the soil at least as deep as it sticks out.  For for the 8 ft. backboard they would have to be driven into the trench floor at least 4 ft.  When used in construction the sheeting material (usually steel) has to be stronger than the force it is going to resist.  In this case the backboard is probably rated for 300 pounds and the lateral force of the soil is over 2,000.  Best case scenario would be that the cave-in knocks the backboard over and creates a void (tee pee or lean-to) for the victim.  My guess is that the backboard would snap if a portion of the wall caved. I do understand that was all there was to work with at the time but working on an unprotected lip to install something of so little protective value just doesn’t compute in my risk/benefit analysis.  At trench rescues with high probability of secondary collapse we have developed a method that offers greater lip protection than traditional ground pads.  These “lip bridges” (one version seen in Hole Rescue #2 post) can be quickly installed during initial actions and left in place during the rescue operation.  The bridges elevate the working platforms above the lip and transfer the load (rescue personnel and equipment to more stable ground.  This doesn’t mean that we do not use traditional ground pads to protect a lip because we do.  Lip bridges simply offer a tactical option for certain conditions. Also seen in the (Hole Rescue #2) post is what we call “cross shoring” which is needed for hole rescues with four wall cave-in exposures.
It is always easy to “Monday Morning Quarteback” an incident.  This is not the intent of this post.  The intent is merely to offer alternative tactical options for similar rescue situations and to create discussion for the blog.   The Pompano Fire Department should be commended for their successful rescue.  Hopefully the department will continue to enhance both rescue training and equipment.

Excavation Shoring

EXCAVATION RESCUE

You are dispatched to a trench cave in with workers trapped.  As you respond, you begin a mental review of the things you learned during your trench rescue training.  Position the fire/rescue apparatus safely back from the trench.  Perform a size up.  Control hazards and people around the site.  Provide lip protection and stabilize the trench walls.  Coordinate panel team and shoring team operations.  Enter the trench, treat and extricate the patient when the benefits and risks are balanced.

     Good, it’s all coming back.  When you step off the truck you see a hole in the ground that is 12 feet deep, 24 feet wide and 40 feet long.  This is an “excavation” rescue and the shoring techniques that you learned in trench rescue school are of no use.  Now what?

HISTORY

The first time this happened to me was just over fifteen years ago when our trench rescue team was sent out on a county mutual aid request.  Wanting to help our mutual aid partners, we improvised a shoring system based on our knowledge of both trench and building collapse shoring techniques.  The walls did not collapse as we performed a recovery of a deceased underground construction worker so what we did must have been correct.   Or was it?
A few years later I responded to assist a different community perform a rescue at another excavation site.  The local fire department had no trench shoring capability and if they had, they wouldn’t have been able to stabilize the excavation walls, which were more than twenty feet apart, using typical trench shoring methods.  This incident prompted me to start experimenting with the use of raker shores at excavations.  We built rakers on the excavation lip and lowered them into the excavation.  We used the design and anchoring techniques for structural collapse shoring.   After applying pressures to the experimental rakers, I found that the typical wooden raker shores used in structural collapse were not capable of restraining pressures that would be common to excavations in soil.  The biggest difference was that the greatest forces in a leaning structural wall are at the top of the wall.  With a trench or excavation the pressures are greatest at the bottom third of the wall.  The design of a typical structural raker system is not intended to resolve those forces.

SYSTEM DESIGN
Despite the set back from the wood raker tests, we were determined to develop a working excavation shoring system.  About six years ago, we started to experiment with pneumatic raker (Paratech) systems in excavations.   In our initial tests on these systems, the weak point was the shore climbing the wall as lateral pressures increased.  It took several attempts but we have now solved that problem by bolting the aluminum Paratech wales to the Finnform panels.   We use high shear strength 1/2″ bolts that thread into T-nuts which are pre-drilled and set into the panel for quick installation.  The panels, wales and struts are then secured (pinned) into the excavation wall with pickets (1” diameter  by 36” long).   We have inch and a quarter diameter holes pre-drilled into the panels for the pickets.  These pickets are spaced across the panels to provide room for swinging sledge hammers.
With the wall climbing issue resolved, our next set of tests on the pneumatic rakers showed a failure point at the base which holds the “raker junction”.   This is the point where the upper and the lower struts come together and meet in an aluminum swivel base at the ground anchor.  Our testing resulted in large forces on the lower shore and this caused repeated failures of the base connector. (you can see one of these failures at http://www.youtube.com/watch?v=glo3hZl1yVQ   Please note that we have replaced the Paratech wall plate (seen in this video) with Paratech Wales.
Currently we have developed equipment (angled “Z” base at the raker junction) and techniques that have tested the “8×8 Excavation Raker”(8′ high x 8′ wide) to withstand forces of more than 18,000 pounds  of  lateral force.  To date we have not been able to cause a failure of this system.

SYSTEM TESTING
The MUSAR Training Foundation does destructive testing on all of the trench shoring  systems that we teach.  We commonly load the wall behind the shores by “back trenching” with a narrow bucket four feet behind the trench or excavation wall.  Then we insert large air bags into the “back trench”.  As the bags inflate they exert force in the “back trench”, pushing to earth towards the trench/excavation shoring system.  With load cells on all struts in the system we can record the forces that the shores resist during testing and compare them to calculated C-60 soil loads.  We use C-60 soil pressures as the testing standard.  We have also tested shoring systems that are being taught by so called “reputable” training companies and institutions and have failed some of them at remarkably low forces.  More on this in a future blog.

BUILDING AND INSTALLING THE EXCAVATION RAKER
The entire Excavation Raker Shore system is built on ground pads on the lip.  To provide rescuers with an eight foot safe zone in a typical (8-10 feet deep) excavation you will need two Finnform panels  (4’x8’), two 8’ aluminum wales, a Paratech 610 raker kit, nailing blocks, 2×6 braces (should be pre-cut) a bunch of steel pickets (1” diameter 36” long) a 6”x6” ground anchor, and sledge hammers.
After the raker is built, it is tied off to an anchor point well behind the excavation lip (usually a couple of pickets) and carefully lowered into the hole using ropes controlled by two rescuers.  At that point a “wall anchor team” climbs the raker down into the excavation with pickets and sledge hammers to drive pickets into the wall.  Simultaneously, a “ground anchor team” drives pickets into the excavation floor (anchor block)behind the rakers.  Since the entire excavation raker system is built and installed (lowered) from the lip, this is the only exposure time that the rescuers experience.  Their exposure risk becomes less with each picket (wall and floor) that gets placed.
This year we have added the “Deep Excavation Raker” to deal with excavations of up to 12’(see picture #4).  A second set of panels, wales and rakers is built and installed similar to the “8×8” raker system.  It rests on top of the first set of vertical wales until the struts are pressured (air system @ 175 psi)and the panels and anchors are picketed into the wall and floor.   To minimize risk, both systems have to be placed then anchored at the same time. To date the “deep excavation raker” is only a prototype  because it has not been subjected to destructive testing but the concept looks very promising.

SHORING TIME
The standard for building and setting the 8’x8′ system into the trench is 20 minutes.  It takes another 10 minutes to complete the pickets and shoot the air pressure to the shores.  The fastest I have seen the 8×8 system built and installed was 14 minutes by members of the Rochester (MI) Fire Department.  At this point we have not timed the construction and installation of the Deep Excavation Raker.  Stay tuned to the MUSAR trench blog for the testing and timing on this system.