CHAPTER. Jones and Bartlett Publishers. NOT FOR SALE OR DISTRIBUTION

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1 CHAPTER Jones and Bartlett Publishers. NOT FOR SALE OR DISTRIBUTION 14

2 Protective Systems in Trench Operations Objectives Explain the proper use of sheeting for trench rescue operations. Explain the proper use of ground pads for trench rescue operations. Describe the proper use of shores for trench protective systems. Describe the techniques for using isolation tunneling for victims trapped in running debris, and the use of shaft tunnels to reach buried victims from remote locations. Specify the procedure for building a class C protective system. Describe the various methods contractors use to stabilize trenches and excavations. Explain the different components and materials used by contractors to shore a trench. Skills Objectives Place ground pads. Install strongbacks without panels. Install same side panel sets. Install opposite side panel sets. Install pneumatic shores. Install timber shores. Install wales as horizontal members to span openings along the trench walls. Build a class C shoring system. Install supplemental sheeting and shoring. Direct the use of sloping, benching, or other commercial shoring systems.

3 After arriving at the scene of a trench incident, you are informed by the contractor that a very deep excavation has collapsed. He explains that when he returned from lunch he noticed that two bicycles were by the construction trailer; however, no signs of bicycle riders are in the area. He further explains that they have had trouble the last couple of days with kids playing in the area. It seems they like going in and out of the waterline that was being installed. 1. What questions will you have for the contractor? 2. What considerations do you have for starting the rescue operation? 3. What resources and techniques will most likely be necessary to handle this incident safely? The equipment we use in trench rescue is fairly basic when compared with other technical-rescue disciplines. As mentioned previously in this book, trench rescue is really just glorified construction work. We build stuff, and we need to build the stuff fast and by the way, it is dangerous while we build it. There are many ways to use our basic set of equipment, and mastering its use is as paramount to your future success as understanding its limitations. Good technicalrescue technicians need to know when the incident scene requirements have exceeded their ability to impact the situation safely. In this respect, they also need a very comprehensive understanding of not only their own techniques and equipment but also the techniques and equipment that contractors use in not so serious but equally dangerous situations. Ground Pads In Chapter 9, we discussed the use of ground pads to distribute rescuer and equipment weight around the trench lip. At this point, we need to discuss the proper installation of the ground pad. In each situation, you will need to decide what kind of ground pad is best suited for the situation. For example, you may want to use a 2 12-inch board on the spoil pile side of the trench and a 4 8-foot piece of 1 2-inch plywood on the other side. Procedure: Placing Ground Pads (Skill Drill 14-1) Regardless of the type of ground pad used, you will want to first approach the trench from the corner (Step ). The corner has the greatest stability. Start by placing the ground pad on the ground at the corner, and then while standing on the ground pad, level the ground in front of you (Step ). After the ground is level, step back and move the ground pad forward (Step ). The process repeats itself until all the ground pads are in the proper position (Step ). In no case should you be in front of or off of the ground pad while you are preparing the area next to the trench lip. Sheeting Of all of the techniques that can be used to make a trench safe, you as a rescuer will use the sheeting and shoring the most. This is for a number of reasons mostly because commercial sheeting systems are designed to be installed before digging begins, or they require near-vertical walls to be effective. Trench collapses do not normally come with all of the walls straight; if they did, you would not be there in the first place. The panels used in the rescue business contain the sheeting material, usually a Shorform or FinnForm panel, with a 2 12 strongback already attached. Having the strongback attached to the panel is not necessary; however, having it already attached allows the panel to be lowered into the trench as a unit at just about any angle that allows you to get a shore from one strongback to the other. With this being the case, a trench training class produces much nicer trenches than a trench collapse call. For example, on real events, you will find that panels and shores often do not line up. Do not worry about pretty. Concentrate instead on the physical forces involved in the collapse and what you are trying to accomplish. As we mentioned earlier, the strongback is the required vertical component in the protective system if standard timber or pneumatic shoring is being used. The only exception is when you are using shoring systems with either the strongback attached, as with hydraulic Speed Shores, or pneumatic shoring, like the Airshore Multi- Shore System, which has a variation of the strongback already attached to the shore. In these situations, the shore can be installed directly between the panels ( Figure 14-1 and Figure 14-2 ). There is always much discussion about the use of panels in the first place, and the panel itself is not considered

4 Protective Systems in Trench Operations Ground Pads For size-up and ground pad installation, always approach the trench from the corners. Place the ground pad at the corner and clear the ground in front. Step back off the ground pad, and move it to the area just cleared. Ground pads in position. Figure 14-1 The Speed Shore has the strong back portion of the protective system already installed as part of the shore. Figure 14-2 The Airshore Multi-Shore system can be installed with spot strongbacks directly to panels.

5 180 Trench Rescue a part of the protective system. In many classes of soil, it is perfectly acceptable to use only the strongback. For instance, in many parts of the country, the excavation is in a class of soil that enables the walls to stand in a most vertical manner unless disrupted by some external force. In this case, it would be acceptable to just use the strongbacks ( Figure 14-3 ). Although this might be acceptable based on the class of soil and also the shoring tables, I have found that rescue personnel feel more comfortable when the panels are used in conjunction with the strongbacks. When this type of system is in place, it is stronger because of the panel and also eliminates running debris as a concern. In addition, depending on where you live, it may be difficult to find a class of soil in which the panels are not necessary. For instance, in Virginia Beach, you are not going to dig a hole anywhere that is not either moisture saturated or sand based; therefore, we elected to teach all of our rescue personnel the system using panels with the strongbacks attached. Now that I have tried to convince you to use the panels with the strongback attached, I must admit that this system makes storage and transportation an issue. When put together, the panels and strongbacks do not stack or fit together well. If storage is a problem and/or you live where there are varying classes of soils, you may want to transport and store them unattached. They will stack very nicely, and if you have predrilled for the carriage bolts, they can be assembled very quickly. The other advantage is that you can use them in any configuration that you want based on the situation presented ( Figure 14-4 ). Setting panels in a trench is accomplished using a variety of methods depending on the condition of the trench and location of the victim. In most cases, the strongback will be facing the inside of the trench with the panel as close to the wall as possible. Care should always be taken when setting panels that one or more of your Mongos do not end up in the trench! You know how it is when you get three or four of them together! Procedure: Same Side Panel Installation (Skill Drill 14-2) When setting panels, you will have the option of doing a same side set or an opposite side set. If you can do a same side set, the panel is moved into place, and the ropes that are tied on the bottom of the panel are held (Step ), while the top of the panel is pushed out and over the trench (Step ). The ropes are then used to slowly lower the panel, keeping it tight to the wall (Step ). If adjust- Figure 14-3 In hard-packed soils, the strongback can be used without the panel. Figure 14-4 Panels and strongbacks can be stored as an assembled unit or stored separately, depending on the limitations of your transport vehicle.

6 Protective Systems in Trench Operations Same Side Panel Installation Place ropes on panel and prepare for installation. Place panel on lip of trench and push out on the top while holding the ropes. When the panel is vertical against the trench wall, lower the ropes so that the panel is set tightly against the trench wall in the desired location. ments of the panel are necessary after setting, the ropes are just pulled up and the panel is moved. As a rule, same side sets are the easiest and fastest but require more room to maneuver your panel team. This ultimately could involve the moving of a substantial amount of the spoil pile. SAFETY As a rule, strive to create a safe area of 12 feet in the trench. Procedure: Opposite Side Panel Installation (Skill Drill 14-3) When it is not possible to set the panel from the same side of the trench, you can use the opposite side technique to set the panels using two 4 4-inch runners. The runners are placed against the opposite side wall with one end of each runner touching the bottom of the trench on the opposite side, and the other ends on the top of the side you are on (Step ). The panel is then flipped so that the strongback is pointing down (Step ). This will allow you to slide the panel down the runners until the bottom of the strongback is against the opposite wall. You can then push the panel upright to the other side of the trench using a pike pole or pull the panel across using a rope (Step ). TACTICAL The opposite side panel set is also a good technique when you have a victim in the trench and additional care has to be taken with panel placement.

7 182 Trench Rescue 14-3 Opposite Side Panel Installation Place runners in the trench so the bottoms are in the desired location when the panel s strongback is installed. The panel can then be pushed or pulled to the opposite side using ropes or a pike pole. Turn the panel over. Place it on the runners, and then lower it in place.

8 Protective Systems in Trench Operations 183 Although there may be some variation in how the panels are set, there is no variation in how many you set. For nonintersecting trenches, the minimum number of panels that will be needed is six. The first two panels are set on each side of the victim, and then two more are set on each side. This creates a working area for the rescue team if digging or patient care is needed. This does not necessarily mean that all six panels should be set before beginning patient care. Remember that every situation is different that is what makes this job so difficult. When you have created a safe area for rescue personnel, let them go to work. That may mean one set of panels with some combination of shores that you deem a safe environment based on all of the conditions presented. Your risk benefit analysis should determine this call. In all cases, you should try to set the first two panels on each side of your victim. Shoring SAFETY Secondary collapse potential is a very real possibility, especially after dirt removal. Make sure that your victim is protected by setting panels and shores over the victim first. After the panels and or strongbacks are set, you will want to make the system safe by installing the shores. Shores are the component of the system that will transfer the forces across the trench, through the strongback, and then into the opposite trench wall. Transferring the potential energy will complete the protective system and give you a safe area in which to work. Procedure: Installing Pneumatic Shores (Skill Drill 14-4) Commonly referred to as shooting the shore, the air system is connected to the shore (Step ). It is then lowered into place using ropes attached to either end (Step ). When the shore is lined up in the proper place, usually done best by someone at the end of the trench (Step ), the signal to shoot and hold the shore is given (Step ). The shooter will then activate the air at the pressure recommended by the manufacturer to extend the shore. At this point, the individual shore type will determine the method that you will use to lock it off. Some air shores are pinned, whereas others lock automatically or have a screw mechanism to lock manually (Step ). The final step is to toe nail the shore to the strongback. In any case, after securing the shore manually, the pressure is released by the installer indicating release (Step ). The air hose is then removed and placed on another shore. After the shores are in place, they create an overlapping zone of pressure on the trench wall. This overlapping pressure stabilizes the trench walls and prevents collapse (as was illustrated in Figure 6 6). While on the topic of what pressure to use to shoot the shores, I would like to offer the following: the manual systems used to tighten and lock shores can exert far greater pressure than the air used to shoot the shore. In some cases, this pressure can exceed 400 pounds per square inch (psi). Thus, the bottom line is that you need to adjust the air pressure based on the situation presented. Because we are trying to eliminate active potential in the soil, I have always found that a good rule is to shoot the shore at a pressure adequate enough to pin the panel or strongback firmly up against the trench wall. Do not let your workers get carried away or let Mongo operate the air. Your objective is to transfer energy, not create it. Another reason not to overpressure the shores when installing them is that when the incident is over you will have to pressurize them to an equal or greater pressure in order to unlock and remove them from the trench. SAFETY The only person who can call for the shore to be shot is the installer. This will help keep him or her from getting hurt by the shore being accidentally activated. The placement of shores in the trench is also a complicated issue. When dealing with air-operated shores and in a rescue situation, you may want to shoot the middle shore first ( Figure 14-5 ). If you think back to the physical forces discussion, you will remember that the most unstable part of the trench is about three quarters of the way down from the top; therefore, you may want to secure this area of the trench first. The other reason to consider this procedure is that in a trench less than 8 feet deep and with a rescue situation, you may want to start patient care with only the first set of panels and one shore installed. If you elect to do this, remember that one shore may be strong enough to transfer the lateral forces of the trench at these depths; however, every situation is different, and you must be absolutely confident that no potential for the soil to become active remains. The kinetic energy in active soil can snap panels and strongbacks, causing a collapse even with the shore in place. After installing the middle shore, you will move your efforts to installing the bottom shore ( Figure 14-6 ). This is the next most dangerous and unstable area and also the area closest to our patient. Following the same procedure as with the middle shore, the rescuer will climb down a ladder beside the panel and shoot the shore. Care should always be taken not to allow the rescuer to get further into the trench than waist high to an installed shore. As an

9 184 Trench Rescue 14-4 Installing Pneumatic Shores Connect air hose to shore and adjust the regulator to the desired pressure. Lower the shore using ropes until it is in the proper position. Use a spotter at the end of the trench to determine whether the shore is level and in the correct location. The installer initiates installation by saying shoot and hold. The shore is locked manually as determined by type and manufacturer. All shores should be toe nailed before the installer indicates release.

10 Protective Systems in Trench Operations 185 Figure 14-6 The bottom shore being installed. Figure 14-5 Middle shore being installed on the first set of panels. example, the person shooting the bottom shore would be allowed to enter the trench between the panels until his or her waist is even with the previously installed middle shore. It is easy then to lean over and secure the shore according to the manufacturer s recommendations. SAFETY Always have the first shoring team members in class 3 harnesses with a tag line while placing the first set of panels and shores. The top shore would follow, with care being taken not to shoot it too close to the trench lip ( Figure 14-7 ). The rule for shoring is to install the middle shore and then split the difference between the middle and top shore and the middle and bottom shore. I recommend that, if possible, three shores be shot for all trenches 6 feet deep or more, regardless of the type of soil. The reason for this is two-fold: First, when in a training Figure 14-7 of panels. The top shore completes the installation of the first set

11 186 Trench Rescue environment, we want our students to install as many shores as possible. This helps to reinforce learning because, as previously mentioned, trench rescues do not happen every day. Second, we want our systems to always be greater than what is required, rather than just meeting the standard. I am always mindful that it is our rescue personnel we are putting in danger, and every precaution should be taken not to compromise their safety. The last thing I will mention about the number of shores actually required is that if you are designing a system and the top shore can be placed within 18 and 24 inches of the trench lip and the bottom shore can be placed within 18 to 24 inches of the bottom and the resulting distance between the top and bottom shore not more than 4 feet, then only two shores would be necessary. That would satisfy the requirements for the protective system. The 4-foot rule no space greater than 4 feet between any horizontal or vertical shoring point is great for designing and building all protective systems. All of this mumbo jumbo talk about shore installation comes down to this: Rescue and training are different. If I am trying to save someone s life, one shore may be enough for me to start patient care; if I am trying to satisfy a standard, two shores with less than 4 feet of spacing between them may be enough. If I am in a recovery situation or I am training, I may put three just to make sure that my folks are as safe as possible. Making decisions like that is what makes our jobs fun. GENERAL As a rule, the best systems are those in which the maximum distance between both horizontal and vertical shores never exceeds 4 feet. done and then the bottom (Steps and ). With each installation, the rescuer is allowed to enter the trench only at waist level to the last secured shore. Because cutting the timbers for shoring is difficult at best, scabs are used to hold the shores in place. It is usually easier to nail the bottom part of both scabs to the strongbacks and to use this as a shelf on which to rest the shore while installing the top scab. Wedges can then be used to tighten the system. Keep in mind that the minimum-sized Douglas fir shore that is approved for class A and class B trenches up to 10 feet in depth is 4 6. TACTICAL Rails that are 2 4, referred to as railing the strongback, can be installed on the strongback previous to setting panels. This will make shore adjustment easier for the installer ( Figure 14-8 ). Wales are horizontal members that are used to span openings along the trench walls, and they can be of the inside or outside variety. As we discussed earlier, they can be made of timber, metal, or makeshift ladders. The length of the wale is entirely dependent on the area that needs to be spanned. Inside wales are used to span a trench panel for the purpose of creating a safe area in a T trench or to create an open space in the middle of a trench ( Figure 14-9 ). The wales are lowered into the trench on the inside of the panels and placed up against the strongback. The shores are then shot to the wales. Outside wales are placed against the trench wall before placement of the panels. They are used to span an opening that may have been created by a slough of the Now for the disclaimer: In every trench situation that involves a recovery, you should never deviate from the manufacturer s recommendation for shore installation. Generally, that means from the top down. TACTICAL Remember to always toe nail the end of all shores to the strongbacks. In this way, if subsequent shores cause the system to become loose, previously installed shores will not fall out. Procedure: Installing Timber Shores (Skill Drill 14-5) Timber shores use a somewhat different procedure for installation. Because a timber shore needs to be measured, cut, and scabbed after placement, the top shore is installed first (Steps and ). Subsequently, the middle shore is Figure 14-8 Railing the strongbacks can make the installation and adjustment of timber shores easier for the shore installer.

12 Protective Systems in Trench Operations Installing Timber Shores The top timber shore is installed. Scabs must be used to secure all timber shores. The middle timber shore is installed. The bottom timber shore is installed.

13 188 Trench Rescue Figure wall. Outside wales are used to span a slough in the trench nothing more than additional shoring put together and installed to address the void area. GENERAL If you are concerned with the stability of your protective system, you can always add additional strongbacks or wales, shorten your shoring zone, or call an engineer for advice. Figure 14-9 wall. Inside wales are used to span a slough in the trench trench wall ( Figure ). After installation of the wales and panels but before the shores are shot, it is necessary to backfill the area between the panels and the trench wall. This will allow the forces to be transferred effectively when the protective system is complete. More information about practical procedures in Chapter 15. TACTICAL All areas of the trench need to be backfilled when there is an open space between the protective system and the trench wall. If a void is not present, no transfer of forces can take place. Supplemental sheeting and shoring is necessary when an area of dirt is removed or falls from behind the panel and into the trench. This creates a void that will need to be filled if it extends more than 2 feet below the bottom of the protective system ( Figure and Figure ). To address this problem, you would construct and install supplemental sheeting and shoring. This type of shoring is Isolation Tunnels, Shafts, and Engineered Systems There is always the possibility that the soil profile will not allow you to excavate an area without the product running back in the trench as fast as you can remove it. Sand, coal, grain, and other similar products are running debris and therefore hard to sheet and shore. In these cases, special systems called isolation tunnels and shafts can be built. Isolation vessels are cylinder objects that are placed over your victim and then worked around him or her as the material is moved ( Figure ). In the case of a coal worker who was trapped in running debris, a 55-gallon barrel with both ends cut out was used. Keep in mind that objects such as the barrel are strongest in the vertical orientation and weakest if laid horizontally. Concrete pipes can also work for this method. A similar method can be used to build and install a shaft. In the case of the shaft, the system will take longer to construct than other types of systems, but this may be your only option for a worker who is trapped in running debris. The engineered class C system is a special system designed by an engineer to address problems created by the very worst type C soil ( Figure ). In this type of system, each 4 8-foot piece of sheeting panel has three strongbacks. These strongbacks are toe nailed to the sheeting

14 Protective Systems in Trench Operations 189 Figure Supplemental shoring is required if digging operations extend to four feet below the last shore. Figure Supplemental shoring is continued as digging operations continue in the trench.

15 190 Trench Rescue Figure Isolation vessels can be made out of a variety of materials and are best when used in situations where running debris is a problem. Figure In very hazardous soils consider the class C engineered system that has additional strongbacks to create multiple contact points for energy transfer. How many additional contact points are created when compared with a normal trench with wales? and then held in place using 6 6-inch wales. The shores are then shot to the point where the wale crosses the center strongback of each panel. This type of system uses many contact points in order to transfer the tremendous forces created by a type C soil surcharge. In all cases, in order to create a protective system that is different from the Occupational Safety and Health Administration (OSHA) standard, it must be certified and approved by a registered engineer. Commercial Techniques There are times when our equipment s capability to address a trench collapse situation is questionable. In these cases, professional engineers and construction people should be called in to assist you with the extrication effort. This does not mean that you give up responsibility for the situation. It just means that you recognize the situation is greater than your abilities as a rescue team. Keep in mind that we do not dig holes for a living; construction people do, and therefore, they are much better at it than we are. Consider using commercial techniques and professional help if any of the following occur: The trench is deeper than 15 feet There has been a massive cave-in Workers are trapped in running debris Environmental conditions prohibit the rescue effort Any protective system that is put in place for either rescue or commercial operations must be capable of withstanding all intended and reasonably expected loads. Predesigned systems are engineered to withstand certain forces. The decision regarding the type of protective system to use may vary based on the type of rescue operation or, in the case of a commercial situation, the type of job, location of adjacent structures, and time. Regardless of the parameters, protective systems are based on a set of factors that are evaluated during each operation. These factors may include but are not limited to the following: Adjacent structures Existing hazards Soil type Water profile and hydraulic table Depth and width of the trench Purpose of operation (rescue versus utility installations) Commercial shoring techniques can be described as either sloping the trench banks to a safe angle, which is sometimes called open cut trenching, trench box, rabbit box, or shield systems, soldier pile and lag shoring, sheet piling shoring, or modular shoring. Sloping and Benching Systems Sloping or benching are methods used for decreasing the angle of a wall to a point that it does not want to collapse. This method reduces the gravitation forces and total amount of unconfined compressive force that is present ( Figure and Figure ). It may also be applicable

16 Protective Systems in Trench Operations ' Max 1 3/4 Figure Sloping reduces the angle of the trench wall to eliminate collapse potential. 20' Max 1 4' Max 3/4 Figure Benching is another technique that reduces collapse potential.

17 192 Trench Rescue during a rescue operation or during a body recovery as a method to safe a large opening. Consider the following when evaluating the need for sloping or benching: Requires tabulated data Requires the use of heavy equipment Is time consuming Takes a lot of room GENERAL Sloping may, in some cases, be referred to as cutting back to the angle of repose. This is the point where the material can support its own weight and is not expected to flow. Keep in mind that any sloping at the scene of a trench collapse should be at least 1.5-foot horizontal to 1-foot vertical. Open-cut trenching can be used in any soil that is not sand or running mud and can be used to just about any depth. The limitations are only in the number of feet from the bottom of the excavation required to obtain the necessary slope. The advantage of this type of trenching is that it allows the contractor to work in continuous digging, laying and backfilling operations. Support, Shield, and Other Systems The trench box or shield provides workers with a safe enclosure in which to work ( Figure ). It is designed to be moved along the trench with an excavator as the trench operation advances. Using a trench box allows the contractor to cut the angles of the walls in a steeper angle than would otherwise be allowed using sloping or benching methods. This method has the advantage of requiring less backfill, although it is difficult to use on long runs with existing utilities in place. Soldier pile and sheet pile are fixed shoring systems that support trench walls. This includes sheet piles that Figure The trench box is a very stable commercial technique used to provide worker protection. can be cantilevered, braced, or tied back to provide ground support ( Figure ). Using uprights made of steel plates or timber, the piles can be pushed into the ground at a depth that is appropriate for the type of soil and depth of the excavation. Piling is installed by pushing it in with a backhoe, drilling a hole to fit the pile, or using an impact, vibrating, or hydraulic hammer. The main advantage of this type of shoring system is that it can easily be maneuvered around existing utilities ( Figure ). Modular aluminum or steel shoring can come in fixed sizes or be adjustable in size. These units come in a variety of shapes and configurations based on the size of the excavation and the type of soil that they will be installed in. In addition to fixed sizes, some of these units are air or hydraulically adjustable ( Figure ).

18 Protective Systems in Trench Operations 193 Figure Soldier pile shoring consists of a set of horizontally installed wales held in place by a set of vertically installed piles. Figure Interlocking steel sheet pile shoring is a commercial technique usually used in deep trenches with tremendous compressive forces. Figure Many commercial contractors use lightweight aluminum trench boxes for trenches of limited depth.

19 2 Trench Rescue Repair Jobs Ron Zawlocki Battalion Chief City of Pontiac Fire Department Pontiac, Michigan If the repair crew can determine the area of the break, they will minimize the amount of dirt that must be removed by digging a trench that will be nearly as wide as it is long. Trenches that are cut for the installation of new underground utilities most often have distinctive long (side) walls and short (end) walls. When cave-ins occur, they are most likely to happen in the long-wall sections. Unless the trench is very wide and unless rescuers will have to operate within the collapse zone of the end (short) walls, only the long walls will be sheeted and shored. Sheeting and shoring training and practices, therefore, focus on the stabilization of the long walls. In older communities, the underground utilities are rapidly approaching the end of their life spans. These failing systems are requiring more and more patch work to keep them running. Repair jobs create trench shapes that are much different from new construction. If the repair crew can determine the area of the break, they will minimize the amount of dirt that must be removed by digging a trench that will be nearly as wide as it is long. The holes that are created by repair crews are always dug in what is inherently dangerous previously disturbed soil. Our trench rescue team has responded to several of these repair type cave-ins throughout the metropolitan Detroit area. The lessons learned that follow are the result of three successful rescues of construction workers. Four-wall shoring. Because the side walls and the end walls are so close in these types of trenches, all four of them must be sheeted and shored to protect the trapped victim(s) and rescuers. In many cases, three of the four walls will slough. Ladder bridges. Slough-ins often leave dangerous overhanging sections of soil above the victim. This soil is unsupported and is held in place only by soil cohesion. Allowing rescuers to step on these unsupported lip areas will likely cause them to collapse into the trench. In order to set panels and place shores, we have developed a procedure that uses fire service ladders to create a safe working platform or bridge across the slough-in areas. The ladder bridge is constructed by placing cribbing on solid ground at each side of the trench lip. A fire service ladder then spans across the cribbing blocks. This keeps the ladder elevated above the overhanging lip area and allows rescuers to work close to the trench wall while installing sheeting and shoring equipment; 2 12-inch lumber is placed on top of the ladder rungs to create a solid work platform. Supporting overhanging lips. Overhanging trench walls present very precarious situations. If they are not handled quickly but delicately, they will wind up falling onto the already trapped victim(s). These sections

20 Protective Systems in Trench Operations 195 of the trench walls can be captured with low pressure air bags, panels, and pneumatic shores. They are commonly used to upright overturned commercial trucks and trailers. To keep the overhangs from falling in, it is vitally important to follow the procedural sequence outlined in Chapter 15 of this book for backfilling the slough trench.

21 Wrap-Up Hot Terms Benching: Cutting back the soil in benches of an appropriate height and width to meet the specifications as determined by soil profile. Isolation vessel: Cylinder objects that are placed over your victim and then worked around him or her as running or loose material is excavated. Rabbit box: Portable trench box made from aluminum or other material that can be set and adjusted on site. Sloping: Process of cutting the soil back to a predetermined angle based on the soil s profile. Soldier pile and lag shoring systems: Z-shaped or H-sheet interlocking piles that are driven into the ground and then held in place with vertical connections at a spacing that is appropriate for the depth of the excavation and class of soil. Supplemental sheeting and shoring: The process used to extend shoring between or under existing shoring systems. Trench box: Term used to describe a premade shielding system that can be placed and lowered as digging operations continue. Wales: Horizontal members, installed on either the inside or outside of panels, to span openings along the trench walls or create a space by spanning panels. Review: Just the Dirt Sheeting and shoring are the primary tools used to create a protective system in a trench collapse operation. Sheeting panels have a strongback connected to them that is used to place the ends of the shores. In most cases, the strongback is the only part of the protective system considered when evaluating the trench for OSHA compliance. A number of techniques are used to place panels in the trench. Two of the most effective are the same-side and opposite-side panel set. The same side set is faster and more efficient, whereas the opposite side can be used when you cannot access one side of the trench or you have a victim near the panel set site. Always set your first set of panels over the victim. A number of different shores and shoring systems are used to construct protective systems for trench operations. By far the most popular in the rescue business is the pneumatic and timber shore. Shores have a proper order in which they are installed depending on the type of shore being used. Supplemental shoring is necessary when digging operations require the removal of soil and it ends up 2 feet below the bottom of the strongback. Horizontal members that cross the strongbacks in a trench are called wales. Wales are used to span an opening in the trench wall or on the inside of the trench to create an open space. In some cases, the magnitude of the collapse prohibits the use of normal rescue techniques. In these events, commercial techniques are necessary. Deep trenches, those over 15 feet, and running debris are a few examples. In these types of events, isolation tunnels, shafts, trench boxes, and sloping/benching may be necessary to resolve the incident. Questions Some of these questions require you to use knowledge gained in other units of this book. This is where you have to start putting all of the tools together! 1. Traditional sheeting and shoring operations used by the rescue service are typically only good in trenches up to a. 25 feet b. 15 feet c. 30 feet d. 10 feet 2. The first set of panels placed at the scene of a collapse should, if at all possible, be placed a. At the weakest part of the trench b. Directly over the victim c. In the area that is easiest to access d. Each operation is different, and therefore, you cannot anticipate where panels are set.

22 Protective Systems in Trench Operations There has been a massive collapse, and you have no walls left that you feel are adequate to support a panel and shore protective system. You may consider a. Using a crane to place a trench box for protection b. Sloping or cutting back to the angle of repose c. Working without the protective system because the chance of a secondary collapse is over d. Both A and B are correct 4. When sheeting and shoring a trench, we are making an attempt to stabilize the unstable and keep the stable from becoming unstable. We accomplish this by a. Taking away the potential for the soil to become active b. Redistribution of the forces within the trench wall c. Taking away the effects of unconfined compressive force d. All of the above 5. Inside waler systems are used for a number of reasons. Considerations in the use of inside wales would be to a. Reduce the number of shores required to build the protective system b. Create an open space c. Create more upright contact points with fewer shores d. All of the above 6. If the stability of your protective system is in question, you should consider which of the following options: a. Add additional strongbacks to each panel b. Add inside wales to the system c. Shorten your shoring zones d. Call an engineer for an evaluation e. All of the above 7. The procedure for installing pneumatic shores is a. Top, middle, bottom b. Bottom, top, middle c. Middle, bottom, top d. None of the above 8. The procedure for installing the initial set of timber shores is a. Top, middle, bottom b. Bottom, top, middle c. Middle, bottom, top d. None of the above 9. When digging operations involve the removal of more than feet of soil below the strongback or panel, you are required to provide supplemental sheeting and shoring protection. a. 4 b. 3 c. 2 d The opposite side panel set is used to a. Set panels on the same side of the trench as the victim b. Protect the victim from being hit by a panel that is being set c. Set a panel from the opposite side if one side of the trench is not accessible d. Both b and c e. All of the above 11. During shoring operations, the shooting of the shore is accomplished by a command given a. By the extrication officer b. By the air supply officer c. By the shore installer d. By the safety officer 12. When placing panels at any trench collapse, you should always strive to create a safe working area by providing a minimum of feet of protected area. a. 18 b. 12 c. 20 d. 10

23 198 Trench Rescue 13. The maximum distance between horizontal shores should not exceed a. 5 feet b. 4 feet c. 8 feet d. 10 feet 14. Which of the following is not true about isolation tunnels? a. Pre-engineered structures should be used. b. An isolation tunnel is used to isolate a victim from a given environment. c. The 55-gallon welded steel drum is strongest when used horizontally. d. Placement of these devices will most likely require rigging and heavy equipment. 15. Sloping and benching is a protective system method approved by OSHA to provide safety for workers in a trench. a. True b. False 16. A variety of shoring systems are available on the market today. When using a pneumatic shore that has a T-handle device or Acme thread, the user can exert what additional levels of pressure on the wall by manually turning and securing this device? a. Not more than100 psi b. Not more than 200 psi c. Up to and in some instances more than 450 psi d. Never more than what can be gained by the pneumatic pressure of the shore

24 Protective Systems in Trench Operations The first shoring team member to enter the trench for placement of shores should be in a a. Class 2 harness b. Class 3 harness c. Class 3 harness with a tag line d. Tag line tied around his or her waist 18. Commercial techniques should be considered if a. The trench is over 15 feet deep b. There has been a massive cave-in c. Workers are trapped in running debris d. Environmental conditions prohibit the rescue effort e. All of the above