TRENCH RESCUE: THE BASICS

BY STEVEN MILLS

Your engine company is dispatched to a report of an injured construction worker in a trench. As the engine approaches the scene, you notice a backhoe working to remove earth from an excavation site and workers at the trench edge waving you to their location. As you approach the site on foot, you notice two ladders leading down into the trench. A construction worker is standing on each ladder; they are trying without success to pull their coworker from the mud. The victim is shouting that a coupling on a water line failed and seriously injured his leg and that he cannot free himself. He appears to be in a sitting position within a trench that appears to be about 10 feet deep. The water level has risen to the victim’s waist. There is no support for the exposed trench walls. The swarm of construction workers and spectators is openly debating various rescue methods. The commotion is drawing curious passersby; the crowd is growing, and emotion is building. You encircle the trench opening.

As the officer of this engine company, your initial actions will dictate the outcome of this rescue not only for the trapped victim but also for all on the scene, including you and your crew.

BACKGROUND INFORMATION: TRENCH RESCUE

Trench rescue, not a typical response for many fire departments, is hazardous for responding personnel. The risk for emergency personnel responding to a “cave-in” is especially high: A collapsed trench or excavation has greater than a 50 percent chance of collapsing again, particularly when rescuers are digging out the original victims. This potential secondary collapse, combined with numerous other factors such as adverse weather, hazardous atmospheres, release of gas from ruptured lines, broken water lines, the number of victims, and department capabilities, makes such a response challenging.

The Occupational Safety and Health Administration (OSHA) de-fines an excavation as “any man-made cut, cavity, trench or depression in the earth’s surface formed by earth removal.” A trench is defined as “a narrow excavation made below the surface of the ground in which the depth is greater than the width, the width not exceeding 15 feet.”

Although OSHA does not regulate trench rescue specifically, 29 CFR 1926.650-652, Safety and Health Regulations for Construction, cannot be overlooked for its usefulness as a guide for emergency personnel. Within this standard, OSHA specifies that employee(s) working in excavations shall be protected from potential cave-ins by a “protective system.” This protective system is used to prevent workers from becoming trapped or engulfed in soil or other material in a collapse.

Systems outlined in this standard include sloping and benching methods, both of which are a means of removing soil from the sides of a trench, thus reducing the weight and pressure being exerted, or a support system to shore the sides of a trench. The protective system does not have to be used if the excavation is less than five feet deep and a competent individual has examined the ground and has found no indication of a potential cave-in. An adequate means of egress, most often a ladder, is mandatory for excavations four feet or deeper and must be provided within 25 feet of lateral travel.


(1) A spoil pile. The weight of this soil, removed from inside the trench, can cause the side of an excavation to collapse if placed too near the edge of the trench sides. OSHA mandates that spoil piles be at least two feet from the excavation’s edges. (Photos by author.)

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SOIL CHARACTERISTICS

Operating at trench rescue incidents necessitates some understanding of soil and its classifications, which are based chiefly on the soil’s cohesive characteristics. OSHA typically classifies soil into three general categories: Type A (clay-type soil), Type B (granular, cohesionless soil such as silt loam and silt clay loam), and Type C (granular soil, such as gravel or sand). Industry must classify soil to ensure that OSHA’s shoring requirements for an excavation are met.

When responding to an excavation or trench collapse, keep in mind that, regardless of the soil type, a secondary collapse is likely. Soil weight is generally 100 pounds per cubic foot and increases according to water content. Effects of the excessive weight are most often apparent in the victim(s), who may experience “crush syndrome” following a cave-in. Any soil that has engulfed and entrapped a victim must be removed from around the victim’s body—obviously first the airway—so that you can gain access to the victim, do a medical assessment and provide the indicated medical care, and extricate the victim. Extricating the victim vertically (using ropes, harnesses, and other tools to extract the victim straight into the air and out of the trench) may save time, since you will have to remove less soil from the trench.

Rescuers operating in the trench must decide whether it is safer and more expedient to move the soil engulfing the victim to another area of the excavation, away from the victim, or from the trench altogether. Pushing or moving the soil to another part of the trench may create an obstruction that would have to be dealt with later in the rescue. Removed soil, often amassed near the sides of the trench by contractors, is referred to as the “spoil pile.” This removed soil increases weight and pressure on the sides of an excavation. OSHA requires that the base of the nearest spoil pile be at least two feet from the edge of the excavation.


(2) Isolating a vibration source.

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(3) Rescuers are engaged in the tasks of placing the initial ladder, positioning ground pads, and moving spoil piles.

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ON-SCENE CONSIDERATIONS

On arrival, rescuers should establish a hot zone and isolate the area (this is essential for controlling the rescue scene), determine the number and location of victims, ascertain the type of work being performed, and shut down all excavating equipment to stop ground vibration (this also prevents coworkers from trying to “rescue” the victim).

Establish a hot zone. The size of the hot zone should be based on the size of the excavation and should be extended to isolate traffic flow and railcar movement, if applicable. Standard dimensions for trench rescue zones are as follows: 50 feet for the exclusion zone (hot zone), 150 feet for the support zone (warm zone), and 300 feet for the cold zone; all equipment and traffic should be at least 300 feet away. Other considerations concerning factors that could precipitate further collapse may be involved for incidents that occur near industrial, process, or agricultural facilities.

Ladders and ground pads. Initially, rescuers should position ladders (at a trench end until the ground pads have been placed), place ground pads, and move any spoil piles that cause concern. Ground pads distribute the weight of rescuers working along the trench sides, eliminating “point loading” of the trench walls. Place the pads completely around the excavation opening, starting at the position of the initial ladder. Lumber is often used for pads, because it is easy to work with, is available, and is economical. Timbers are sturdier and do not bow, as plywood may. Often timbers are laid and covered by plywood sheeting, to provide more solid footing for personnel.

Once the pads are in position, place additional ground ladders to meet rescuers’ exiting requirements. Remove any spoil piles within two feet of the excavation edges while placing the ground pads. Moving spoil piles to a safe distance from the trench edge is often labor intensive and involves numerous rescuers using shovels and other hand tools. You must plan for the availability of sufficient personnel for this phase of the operation.

Victim information. Information about the victim(s) is needed to determine if the incident will proceed as a rescue or a recovery. Work with the foreman or other witnesses to the accident who are in the trench to determine the number of workers believed to be trapped and where they may be located. NFPA 1670, Standard on Operations and Training for Technical Rescue Incidents—1999, offers some clues for identifying probable victim locations, which include the presence of food and drink containers, tools in the trench, “cat” or tire tracks, and sounds.

Beginning the search. A good place to start a search is at the end of a pipe string. (Excavators lay pipe end to end along the side of a trench; these pipe sections are then progressively lowered into the trench and secured.) Some excavation sites require that pipes be “bedded” with stones, which are commonly dumped into the trench and spread by workers. Tire or “cat” tracks perpendicular to the trench may indicate where the loader dumped the stones and possibly hit the victim. Inquiry into the type of work being performed within the excavation is necessary so responders can prepare for such issues as hazardous materials, utility involvement, and confined spaces.

Sounds detected could also indicate that workers found a safe haven within a pipe at the time of collapse and are attempting to indicate their position.

NFPA 1006, Standard for Rescue Technician Professional Quali-fications, contains provisions for the rapid, nonentry rescues of victims at trench incidents. This can be accomplished when the size-up reveals that the victim “requires only a ladder to leave the trench or a shovel lowered to him to dig out a trapped foot.” Under these conditions, the victim would be able to leave the trench before a secondary collapse occurs.


(4) Utility system pipe within the trench. Utility companies should respond and control their services at the incident site.

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(5) A pipe string. Pipe sections laid end to end along the sides of a trench are lowered into the trench and secured. In some cases, the pipes are “bedded” with stone, in which case a loader drops the stone into the trench and workers spread the stones.

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(6) A rescuer diverts rainwater.

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Utilities. Utilities are often found running through and around trench sites. Request that the responsible utility companies respond and control their respective services. Support unbroken utilities when possible to prevent the release of product.

Environmental considerations. Anticipate that hazardous materials may be involved at every excavation. Look for indications of their presence, and ensure that you have a means of mitigating the involved material on hand. Monitor atmospheric conditions for air quality before personnel enter the trench. Acceptable limits for oxygen are 19.5 to 23.5 percent; concentrations below 19.5 percent are considered oxygen deficient; those above 23.5 percent are considered to be hazardous oxygen enriched atmospheres and pose a flammability hazard. Flammability is measured as a percentage of a material’s lower explosive limit (LEL) and upper explosive limit (UEL); and the LEL should be less than 10 percent for personnel to enter and remain in the trench.

Toxicity levels are specific to individual materials and should be assessed on this basis. Monitor carbon monoxide to ensure that exhaust from equipment and tools operating at the rescue scene is not collecting within the excavation. At-mospheric conditions within the trench may be improved by ventilating the space. Ventilation is also useful in making conditions tenable for rescuers and improving the comfort level of the victim(s). Temperatures within the trench are often cooler than those at grade level; utility companies can provide heated ventilation.

Water level within trench. Do not allow standing water (from rain or a broken water line, for example) to collect within the excavation, or the trench may collapse. The water level should never be allowed to reach to the level of the victim(s) within the trench. Support personnel should divert flowing rainwater from the rescue area and eliminate standing water from the trench.

Weather conditions. They may negatively affect rescue operations; therefore, have plans for dealing with such circumstances in place before responding. Incidents that occur during extremely cold temperatures force rescuers to deal with frozen ground and ice/snow accumulation, which typically slow progress.

Victim extrication. Ensure that the head and face of the victim in the trench are protected against falling debris and objects.

NFPA 1006 discusses the use of cribbing for stabilizing heavy loads, providing a base for lifting, or maintaining a lift. Support personnel should be used topside to prepare and ready tools needed for rescue within the trench and to anticipate and plan for lifting an object that is entrapping a victim. NFPA 1006 suggests establishing an extrication sector to coordinate preparing, assembling, and implementing tools to prevent unwarranted delays that can affect the victim’s survivability.

Sometimes, you may have to use a dirt vacuum truck or a dirt knife to help break up and remove the soil from around an engulfed victim. NFPA 1670 discourages the use of heavy or mechanical equipment and/or mechanical winches to physically lift, pull, or extricate victim(s) from a trench, but it acknowledges that there may be circumstances when heavy equipment may be necessary for accessing victims of trench and excavation collapses. Such efforts may be employed when they are appropriately supervised and after considering the negative impact these actions may have on the victim and the trench.

Disentangling and removing victims are challenging and time-consuming tasks. Completely remove the soil on and around the victim so he can be removed without sustaining additional injuries, which would be the case if you tried to remove the victim before he was completely unburied. The patient may also be pinned or trapped by objects such as large pipes and boulders. Under these circumstances, rescuers will be challenged to use their initiative and ingenuity to free the patient. Equipment such as small shovels, bottle jacks, air bags, and cribbing may be needed.

Rescuer safety. NFPA 1670 states that a rapid intervention team (RIT) consisting of at least two rescuers at or above the capability level at which the incident is operating be available to rescue a member or a team if the need should arise.

Rescuer rehabilitation. Trench rescue operations are physically demanding and are even more taxing in extremely hot or cold temperatures. Keep this in mind when preparing a schedule for regular personnel rotation. Rest and rehabilitation are needed to reduce rescuer fatigue and prevent injuries.

Implementing the incident management system (IMS) and an accountability system early in the trench rescue operation will ensure that the necessary tasks will be sectored and sufficient personnel are available to perform them. As with any intricate rescue, a strong commitment to teamwork and communications helps to ensure a successful outcome.

STEVEN MILLS is a career lieutenant with the Ridge Road Fire District in Rochester, New York. He has an associate’s degree in fire protection, is a nationally certified fire instructor I, and is a New York State-certified instructor in basic trench collapse concepts.

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