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ARK Technical Rescue Services, Inc. 5630 Flagler Drive Centreville, VA. 20120 (703)378-0855 Office (703)378-0855 Fax Also |
ARK Technical Rescue Training Services
TRENCH RESCUE-PATIENT EXTRICATIONFriday, June 29 2007 INTRODUCTION Trench rescue situations are infrequent occurrences, yet they pose significant difficulty for rescuers when they happen. These incidents are complex operations that require unique tactics, procedures and equipment. The US Federal Occupational Safety and Health Administration, (OSHA), states that accidents in excavation work occur more frequently than accidents in construction in general. OSHA also states that trench cave-in accidents are much more likely to result in fatalities then other construction related accidents, and that the fatality rate for trench work is estimated to be as high as 112 percent greater than the rate for construction in general. Trench accidents can create a myriad of entrapment problems for rescuers. The hazards associated with these operations include, cave-in of surrounding soil, hazardous atmospheres, and utility hazards to name a few. Trench rescue training programs focus a great amount of time towards proper shoring techniques and hazard mitigation requirements. These are important job performance requirements that must be met to successfully operate at a trench emergency. However, as rescue organizations develop their training programs to meet trench rescue performance requirements it is important not to overlook the actual extrication requirements associated with trench rescue. Extricating a patient from a trench emergency can be difficult and time consuming, and often times involves more then just digging dirt. PHASES OF A TRENCH COLLAPSE The collapse of surrounding soil at a trench site can occur in various patterns. It can include the sliding of spoil material or bedding rock that was placed too close to the trench opening into the trench . Trench walls can shear off in large homogenous sections, the belly of the trench can fail and fall out into the trench, or a large section of the upper lip of the trench can fall off. Soil is extremely heavy and weighs approximately 100 lbs. per cubic foot depending on the moisture content and other factors. When a cut is made in the earth’s surface the trench walls can be visualized as a column of soil that weighs 100 lbs. per cubic foot for each foot of trench depth. Thus if the trench is 10 feet deep, the column of soil that is the trench wall will weigh about 1000 lbs. and thus exert a vertical force of 1000 pounds per square foot on whatever it rests on. This column of soil also exerts a horizontal force in all outward directions that is equal to one-half the vertical force. In the case of the 10’ trench, the soil column exerts an outward force at the base of 500 lbs. per square foot. The outward force increase with the depth of the trench, and soil blocks at the bottom of the soil column theoretically tend to compress and bulge out. Prior to soil being excavated from the earth’s surface these soil columns are stable and held in equilibrium by the other surrounding soil columns. When an excavation is made, the void created, (the trench) results in de-stabilization of the trench columns along the trench walls. Due to the weight of the soil and the increased outward pressure in the trench walls as the depth increases, soil in the trench walls may not be able to support its weight and the weight of the soil above. When this occurs, the wall will fail, shearing off and breaking away from a stable position. This commonly occurs in three phases, beginning with the trench wall moving into the trench at its lowest level near the trench bottom. This initial collapse results in an undercut area of the remaining trench wall and creates a large unsupported overhang of soil. This is followed by phase two where much of the overhanging section falls into the trench, and may result in a smaller unsupported cantilever of soil near the trench lip. This unsupported trench lip is held in place only by the cohesion with the soil columns around it and will finally fail as phase three. So why is this important for rescuers to know? Because there is typically some time lapse between phases and rescuers may arrive while the collapse is still in phase one or two. This means that the rescuers will then be exposed to a secondary collapse potential during shoring and entry operations. It also means that just because you might have a partially buried patient when you initially arrive, you may have a total burial problem that occurs prior to getting shoring systems in place to control the secondary collapse problem. INITIAL HAZARD MITIGATION The potential for secondary collapse of the surrounding trench walls is not the only hazard that must be controlled prior to beginning extrication operations. Although the installation of a competent shoring system is a primary hazard control requirement, rescuers must also control the trench atmosphere to assure a safe work environment for rescuers. This is accomplished through atmospheric monitoring and ventilation of the trench. In addition, safe access and egress from the trench must be assured by placing ladders within 25 feet of where rescuers will enter and operate in the trench environment. Eliminating or controlling vibration sources such as road traffic or heavy construction equipment, which may cause a secondary collapse, is needed. Managing utility issues such as leaking gas lines or unsupported and exposed electrical conduit is also necessary. Additionally, water accumulation in the trench is to be included in the hazard control phase of the operation. ENTRAPMENT PROBLEMS As mentioned above, the entrapment problem at a trench collapse can require more then just digging dirt. Just as in the case of vehicle extrication, rescuers must be ready to utilize a variety of tools to remove the entrapping material from around the patient. These entrapment problems can include various types of soil, some of which will be easy to dig and remove by hand. However, various soil types will be found, and some very hard soil types will create difficult digging requirements. Two trench rescue events that this author engaged in required rescuers to utilize pneumatic chisels to break the soil apart for removal. Rocks and boulders can also create difficult extrication problems where lifting or chiseling will be required. Construction materials such as timbers used for shoring, pipes to be placed as utilities, or concrete from unsupported sidewalks or curbing can fall into the trench creating extrication problems. A 13-hour trench rescue operation that the author participated in included loose timbers as part of the entrapment problem. The timbers were placed into the trench by initial responders in an effort to protect the victim from further collapse, however subsequent soil movement pushed the timbers into a position that they became a hindrance to the rescue efforts. Hand tools and other equipment that are used by the construction workers in the trench may become part of the extrication problem. At one trench rescue incident the collapsing trench wall wedged a ladder, used for access into the trench, against the victim. At another trench event, the wooden handle of a shovel used by the victim was pinned against his torso by the weight of surrounding collapsed soil. Although rare, heavy equipment has been known to overturn into an open trench, which can result in a difficult lifting operation. In one similar incident that occurred in Fairfax County, (VA), a car left the roadway of a limited access highway and fell into an open trench that was supported by a steel trench shield. The driver was ejected from the vehicle and sustained fatal injuries. The rescuers were lucky that the trench shield already stabilized the trench walls, and that the victim was not pinned under the vehicle. In addition, heavy construction equipment that has overturned into an open trench has been reported in OSHA Fatal Facts publications. EXTRICATION TECHNIQUES Soil Removal The primary entrapping material at a trench collapse will be some type of soil. Whether this is a result of a spoil pile slide, a shear wall collapse, or a slough in of the trench belly, the result will be the same; the need for rescuers to uncover the victim’s head and chest area as quickly as possible, administer patient care, and then continue to remove additional soil to completely uncover the victim. Soil removal will primarily be accomplished though the use of hand tools. Small entrenching shovels, like those used for camping, work very well for this purpose for two reasons. They are small and work well in the confines of a trench environment, and their use allows for limited leverage, so that rescuers can work gently around a victim’s body that is covered by soil. Typically the soil is then placed in small buckets for removal from the trench. In some situations, other small digging tools such as hand trowels, or post-hole diggers can be advantageous for removal of a rock or soil from a confined area where a shovel won’t fit. As rescuers install shoring systems, begin to remove soil, and then are required to install additional supplemental shoring; the work area around a victim will continue to get more and more confined, limiting the use of shovels in some instances where a foot may be trapped and difficult to uncover. In these situations rescuers will be required to dig out a larger area around the bottom of the trench to increase access to the victim’s lower extremities, or utilize smaller tools for reaching and digging around a leg and foot that is still trapped. It is important to determine the positioning of the victim’s body as digging begins. If the victim is lying down in a horizontal position, it will be advantageous to square out the bottom of the trench, as the body is completely uncovered. This will allow the trench floor to remain fairly level, which will ease patient packaging as the victim is uncovered. If the victim is found in a more vertical position, standing up, the digging will be more difficult, requiring additional soil to be removed as rescuers dig down to uncover the lower extremities. This will typically result in a hole being dug around the victim. When this occurs, the removal of material around the lower extremities below the knee will become very difficult due to the limited access. Vacuum Devices In some situations soil around the victim can be removed using mechanical vacuum devices. These vacuums can be hand held or truck mounted devices and this process is known as vacuum excavation. Vacuum excavation consists of two phases, reduction and removal. Reduction is the initial phase of the operation and the intent is to reduce or fracture the soil into small pieces. This can be accomplished by using water, air, or mechanical means. At a trench rescue, the water reduction method, which is the most effective, is not very practical due to the potential hypothermic effects it may have on the patient. The air operation can be accomplished by using a device known as an air lance that uses airflow from a high volume air compressor to break the soil into small pieces. Mechanical reduction, which is the slowest method, can be accomplished by using shovels or chiseling tools to break up the soil. Reduction operations are then followed by the removal phase where the material that was reduced in size is removed from the trench by the vacuum device. These vacuum devices can be hand held devices powered by a separate high volume air compressor, or they can be fully self contained mobile units or skid load units that have their own air supply, and holding tank for the soil that is removed through the vacuum system. Manufacturers of these vacuum units offer several sizes and capacities to handle a variety of jobs, including the capability to siphon off 295 cubic feet per minute of spoil material from as far away as 200 feet from the material. Cut back Operations with Heavy Equipment Significant trench collapse incidents may result in the total burial of victim(s), which will require rescuers to remove a great deal of soil during extrication. This can be very time consuming and labor intensive for rescuers. One tactical approach that can be considered is the use of heavy equipment to perform a cut back operation. Although the use of heavy equipment such as digging with the bucket of a backhoe around a victim is typically considered taboo, cut back operations can be very effective in certain situations where it is an obvious recovery situation. This tactic has been used twice at trench collapse recovery operations that the author was involved in. Cut back operations refer to the utilization of heavy digging equipment to dig a parallel trench or a hole to create a void, so that the existing trench walls can be pulled away from the trench to lessen its depth, or to slope the walls back to the maximum allowable slope. This tactic eliminates secondary collapse hazards and allows rescuers to walk into the trench area to complete the extrication by hand. Determining the mode of operation, (rescue vs. recovery), and performing a thorough risk-benefit analysis will drive your heavy equipment use decision. When rescuers are considering cut back operations as a tactical option, it is important to consider what impact the superimposed load and the vibrations of the heavy equipment will have on the stability of the existing trench walls. It will also be adamant that rescuers confer with experienced and knowledgeable heavy equipment operators in order to make the best decisions regarding the application of this tactic. It will be extremely important to assure that the equipment operator is well trained, experienced, has a calm demeanor, and is clear on what rescuers wants accomplished. As with any digging operation, you must have knowledge of the presence of any underground utilities to avoid damaging them and creating additional problems. Chipping and Cutting Operations In addition to entrapment by collapsing soil, extrication problems as mentioned earlier may include entrapment by tools, ladders, timbers, concrete, pipes, or other construction materials. When rescuers are confronted with this situation, extrication options will include chiseling, or sawing materials to free the victim. Pneumatic chisels, electric rotary hammers, or demolition hammers can be used quite effectively to break up rock, shale, and boulders to free an entrapped foot, arm, or leg. Rocks can be reduced to smaller pieces to ease removal by buckets from the trench. In one trench collapse incident that the author managed, the victim’s ankle and leg were trapped by a boulder that shifted out of the trench wall. Air chisels were used to chip away at the rock in order to remove enough material to free the victim. Cutting with hand or power saws may be required when a victim is pinned by tools, timbers, or other materials that were involved in the collapse. Reciprocating saws work very well for this application. These tools are small enough to be used in the tight confines of a trench and can be used in close proximity to the victim by a skilled operator without causing harm. Cutting can also include the use of a knife or EMT scissors to cut a work boot, shoes, or a construction workers tool belt that may be impeding their rescue. Lifting operations Where victims are pinned by pipes, boulders, concrete, or other construction materials, a lifting operation may be the best tactical option for removal. Lifting operations in the trench can be accomplished in several different ways. Air bags can be used to lift a rock, pipe, or other entrapping item. This option presents several challenges. First, the base under the air bag must be built up in order to distribute the load over a large segment of the soft soil, so that the air bag does not sink into the trench bottom as opposed to lifting the load. This is similar to distributing the weight of the outriggers on an aerial ladder over the surface of the ground pads. This can be accomplished using a square of plywood that is larger then the air bag being used. The plywood square should be at least ¾” thick. This will require additional digging and removal of material under the item to be lifted for effective placement of the bag and ground pad. In some hydrostatic soil conditions even the use of a ground pad may not keep the bag and pad from sinking into the soil when the lift is initiated. In this situation another lifting method must be considered. Air bags can be used on the outside of the trench in combination with slings, timbers, rigging, and/or bolting devices to complete the lift of a pipe, boulder or concrete material. Rigging refers to materials such as rated fabric lifting slings, wire rope, chain, cable, and shackles that are designed for attaching to and lifting materials. Air bags are placed on each side of the trench and large timbers such as 6” x 6” s are then placed across the trench. Slings, bolting devices, and rigging materials can then be used to make an attachment between the item to be lifted and the timbers that are laid across the trench. All slack is removed from the rigging prior to starting the lift. The air bags are inflated and the entrapping material is lifted as the timbers are raised by the air bags. The use of bolting in this application is effective when the user is well trained and clearly understands the application guidelines from the manufacturer. Allowable bolting distances such as the minimum distance between bolts, distance to the edge of the materials being lifted, and minimum embedding depth are all important requirements for effective use of bolting techniques. Bolting, rigging, and slings can also be used in combination with heavy equipment for lifting. If this option is considered it is important to evaluate the impact on trench wall stability that the increased superimposed loads and the additional vibration from the machine will have. Whatever method of lifting is used, stabilization of the material being lifted, and control of the lift will be important. Cribbing must be added as the lift progresses to assure that the material will not settle back down on the victim as the lift progresses. EXTRICATION PLANNING AND SUPPORT OPERATIONS The incident commander or rescue officer must continually forecast the needs of the rescue operation. As incident information is gathered, the officer tasked with developing the rescue plan must anticipate tool needs. If the anticipated tools are not available on scene or on responding units, they should be requested early on in the event. Multiple rescue plans should be developed. The rescue officer, incident commander, and others should brainstorm potential rescue options and then set incident objectives for inclusion in the incident action plan. Rescuers must coordinate their efforts with the emergency medical personnel on the scene so that patient care can be initiated as earlier as possible. Once the trench has been effectively shored and hazards mitigated, EMS personnel should be allowed access into the trench, under supervision, to administer care to the patient prior to extrication. The rescue officer must anticipate tool usage and the area needed for tool operations and patient packaging. Make sure to shore a large enough area to allow at least two rescuers to work safely inside the trench to perform digging, extrication, and patient packaging. A common shortcoming that the author has seen at actual trench rescue events and during training is for rescuers to short cut their own safety by installing too little shoring in order to save time to perform the rescue. This has typically resulted in rescuers or victims being exposed to UN-shored areas of the trench, or victim being exposed to UN-shored areas of the trench during patient packaging and removal. Rescuers must anticipate and be prepared to install additional shoring as more trench wall is exposed during digging operations. Continuously assess the competency of the shoring system as the extrication progresses. As pipes are lifted, soil is removed, or victims relocated, exposed trench walls may need to be shored, or modifications made to the existing shoring system. Make sure that tool usage, lifting of objects, rescuer movement, or patient removal activities do not impact the stability of the installed shoring system. SUMMARY Trench rescue situations can create very complex extrication problems for rescuers. Collapsing trench walls, displaced boulders, utility piping, and other construction materials can all potentially be obstacles for rescuers to overcome. In order for a trench rescue team to perform competently, they must be skilled, creative, and prepared to mitigate a variety of entrapment problems. This preparedness can be accomplished through effective planning, and the inclusion of extrication problems as a standard part of trench rescue training programs. |
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© 1999-2006, ARK Technical Rescue Training Services, Inc.
Updated: Sunday, October 29, 2006