The prevailing question of trench rescue is: How do we do it faster and safer?
Trench rescues have very high morbidity rates because the forces imposed on the victims through soil weight are unforgiving. The window of opportunity to enter the trench and relieve that pressure is very small.
Additionally, the likelihood of further engulfment or secondary collapse poses such a significant risk to rescuers that we have to establish engineered systems that will truly protect us.
With this being the driving mechanism, I am a firm believer that the approach and layout for trench rescue makes all the difference in the world.
We were indoctrinated into the “technical rescue” way of performing trench rescue until we were exposed to some industrial theories and techniques that were shared with us by Dennis Hobart of Baker Corp.
There are seven essentials that emerge through blending these industrial concepts with technical rescue concepts that will radically impact the speed, safety and efficiency of a trench rescue operations.
- Consider removing the bottom of the pop sickle stick or strong back so that it is flush with the bottom edge of the trench panel.
- Acquire a significant cache of bridging, preferably corrugated aluminum or steel, to frame out the trench.
- Increase the cribbing cache to support the bridging with remote contact points.
- Use bridging material as slides when placing trench panels.
- Acquire low-pressure trench bags for slough operations and trench wall deviations.
- Stop using timber and mechanical shoring. Pneumatics and hydraulics provide a wide array of solutions that will fit a variety of budgets and are remarkably faster and more effective.
- Use techniques and tools that completely shore the trench from the topside.
These seven essentials require training and resources but yield tremendous returns. In this article we will discuss essentials one through four. Essentials five through seven will be discussed next month.
Strongback augmentation
Trench panels should include a center strong back. Some applications used around the world apply spot-shoring techniques or panel designs without a strong back. Engineering and testing data shows that these options will fail at much lower forces than panels engineered with strong backs.
Most panels are designed with strong backs (2 x 12 feet) that extend above and below the 4- x 8-foot panel by 12 to 24 inches and are fastened to the panel with recessed, engineered carriage bolts. The downside of this design is the bottom 12 to 24 inches of the trench wall is left untouched and ultimately not shored.
This is particularly evident when a slough zone is being back filled with soil and the soil continuously spills out at the bottom of the panel. The advantage of this design is that the strong back acts as a pivot point when placing the panel and facilitates manipulation of the panel during setting operations.
The proposed essential removes the lower section of the strong back providing complete coverage of the trench wall. The advantage is a safer trench.
This holds particularly true in trenches with standing water and propensities for bell pier collapses where the lower portion of the trench is a grave concern. The disadvantage of this design is the loss of a center pivot point, which can make manipulating the panel during setting operations more difficult.
Bridging and framing
Traditional approaches to trench rescue use bridging to span the trench or slough zones. Industrial applications often eliminate ground pads in lieu of bridging because it requires less material and is more versatile.
Framing out a trench is a relatively common practice on the industrial side. This is relatively unheard in technical-rescue circles where bridging is typically dimensional timber that is of adequate width to stand on and perform work (2 x 10 or 2 x 12).
The industrial side uses corrugated lightweight steel that is 12-inches wide and comes in lengths ranging from 4 to 20 feet. These bridging elements should be built up on the ends with cribbing so that the material is stable and does not contact the immediate soil surface around the trench.
Timber bridging bows excessively under lateral loading compared with corrugated metal. It also cannot be interlocked effectively, whereas the corrugated material can be married flange to flange to create greater width platforms that are stable and relatively rigid.
The proposed application follows a very systematic approach to the trench.
Step one
Approach the side of the trench where the victim is located and place three ground pads with the 4-foot edge at the trench lip. The center ground pad should be where the victim is located.
This creates a spacing template for a six-panel set and maximizes the distance from the trench for the initial placement of load-distribution material.
Once these three ground pads are established, place the rest of the ground pads to cover the work zone. Advance bridging material across the trench at each end of the 12-foot zone identifiable by the ground pad placement. This bridging should be long enough to extend at least 4 feet past the walls and lips of the trench.
Step two
Orient additional bridging parallel to the trench walls and place it on top of the perpendicular bridging already in place. Advance it until it is positioned above each trench wall so that is vertically in line with the bottom line or joint of the trench floor and wall.
This accomplishes two things. It creates a straight edge for clean horizontal and vertical placement of panels and it establishes a working platform for all of the personnel working near the lip of the trench.
When the parallel bridging rides on top of the perpendicular bridging, a slough or failure of a wall section will not result in personnel spilling into the trench. They will all be left standing on top of the bridging.
The disadvantages of this essential are the requirements for more resources and training. This also may sound more time consuming. However, a trained crew can accomplish this in less than 5 minutes.
Cribbing contact points
Place cribbing layers under the bridging joints and ends to create platforms that have limited contact with the surface soil. This limits the surface loading and greatly reduces the likelihood of point loading causing secondary collapse.
By increasing the working height of these platforms, more advanced applications are also facilitated. For example, intersecting trenches such as “L” trenches that have unstable interior corners can be spanned in a variety of ways that still allow panels to be placed or slid underneath the bridging.
Another example is advancing low-pressure airbags and hoses under the parallel working bridges. Gaps between the bridging and ground allow these placements to be done with ease. Wedge packs should also be a part of this cache to fill those necessary voids and make the platforms as stable as possible.
Panel slides
Using bridging material as slides for the panels will help ensure that the panels are placed safely, accurately and with ease. The first set of panels should go where the victim is or is presumed to be.
Place two slides into the trench that will capture the opposite side wall and floor joint and progress up to the near side wall and lip. These slides should extend above the trench lip. Use a 12-foot slide for an 8-foot-deep trench.
Place two rescuers on each side of the trench panel and one rescuer on the strong back. This panel should be oriented strong back down. All three rescuers should pick up the panel and advance it to the slides.
Have the slides spread apart just enough to accommodate the width of the strong back. Place the panel on the slides and lift the strong back while the two side rescuers control the descent of the sliding panel with the panel ropes. The panel should slide down and make optimal contact with the lower corner.
Establish a receiving crew on the far side of the trench and direct the panel into a vertical position by pushing the slides and panel to the far side crew. Once the panel is in position, the far-side crew pulls the top of the slides towards them, which redirects the bottom side of the slides to the near side lower corner.
The near side crew then picks up the second panel in the same fashion but the strong back is now oriented up. Advance the panel across the parallel bridging until the bottom edge of the panel contacts the slides. Control the descent with ropes. The panel should come to rest in the near side wall and floor corner.
Predictable performance
By simply shifting the slides back and forth across the trench and maintaining a width gap just adequate for the strong back, both panels should end up directly across from one another. The use of the top side frame work should result in vertical panels.
This is imperative for shoring to perform in a predictable fashion. There is a very limited allowance for deflection in shores both vertically and horizontally. Shoring that is not engineered correctly will fail catastrophically under load.
Additionally, losing a panel while placing it is an extremely heavy edge impacting the victim, causing significant injury if not death. Slides establish bridges above the victim, which prevent this type of mistake.
Slides also create ideal floor and wall marriages. This help reduce bowing of the strong backs and inaccurate measurements or inability to drop shores in.
Watch the video to fully understand these essentials, and then put them to the test. Take your trench team out and see if these don’t increase the speed, safety and efficiency of your operation. I’d love to hear how this impacts your approach to trench rescue.
