BY MICHAEL DALEY
Today’s emergency services must be prepared for any emergency that may arise within the jurisdictions they protect. Occupational Safety and Health Administration (OSHA) studies show that many workers and rescuers have been injured or killed needlessly in trenches that have collapsed suddenly, with little or no warning. The public has come to rely on the fire service to help those trapped by trench collapses. Although some first-in companies may not be trained in this area, they can take specific actions to help ensure a successful rescue.
BASIC TERMINOLOGY
First, the initial responder should understand some basic trench terminology and some safety issues that can arise when working around a trench collapse. A trench is a temporary excavation in which the length of the floor exceeds the width of the trench. It is also common for the height of the trench walls to exceed the width of the floor.
Sections of the trench are as follows:
- Wall or face—the side of the trench from the top of the lip to the trench floor.
- Lip—the top two feet of the trench wall.
- Belly—the center section of the wall, from the bottom of the lip to the top of the toe of the trench.
- Toe—the bottom two feet of the trench wall, where it contacts the floor.
- Floor—the bottom or base of the trench.
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 (3) Crews work to remove the spoil pile from the lip of the trench. Note they are working from ground pads that are moved in as the pile is removed. |
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Trenches may be dug for a variety of reasons—to install storm sewers and sanitary systems or to bring electricity, gas, water, or other utilities into homes, for example. Regardless of the reason for the trench, workers should follow OSHA 29 CFR 1926.650, 651, and 652, which outline requirements and safety regulations for operating safely in and around trenches. As examples, the OSHA regulations say that any trench deeper than five feet is to be shored for support and that an engineer-designed trench stabilization system must be installed in any trench more than 20 feet deep. If no shoring option exists, the trench walls can be dug down to the angle of repose, which will vary according to the type of soil encountered. This angle is best expressed as the ratio of horizontal distance to vertical rise of the trench (H:V). Unfortunately, many of these regulations are ignored or waived, primarily for speed and profit.
REASONS FOR COLLAPSE
Statistics show the following:
- Most fatal trench collapses occur in trenches less than 12 feet deep.
- Depending on the trench depth, soil can fall from 15 to 45 miles per hour, which is the reason most victims are found in the running position when recovered.
- Soil weighs on average approximately 100 pounds per cubic foot. Taking this into consideration, it is feasible that a victim with two feet of soil covering his torso could have almost 800 to 1,000 pounds of soil on his upper body, making it impossible for him to breathe.
Trenches can collapse for a variety of reasons. The most common is the absence of required, adequate shoring materials to render the trench safe. Soil has a natural tendency to push and compress in all directions, and the dug trench is a disruption in the soil that will result in the soil’s taking the path of least resistance and result in a collapse if the trench is not shored.
Other factors, including the following, can compound an unsafe situation and cause a collapse:
- Previously disturbed soil. Digging in such soil, even if it has been filled in for a long period of time, can cause a collapse.
- Intersection trenches. The areas at which the two trenches meet are inherently weak.
- Vibrations. Construction equipment or motorized shovels operating too close to the trench can cause collapse, as can traffic moving through the area.
- Placement of the spoil pile. If the spoil pile (soil removed from the trench) is too close to the lip of the trench, the resulting narrow right-of-way restricts working room. The spoil pile is required to be at least two feet from the trench lip.
- Drying of exposed trench walls. Moisture is needed to bind soil together. Without it, soil becomes weak and begins to fail. Dry walls are common in trenches that have been open for a while.
- Heavy rain runoff. It adds weight to a spoil pile that is close to the trench lip and can also wash away the trench walls’ cohesive properties.
INITIAL RESPONSE
First-in companies at a trench collapse with a trapped victim can help prepare the scene for the arrival of the technical rescue team. Once on-scene, the incident commander (IC) must restore order at the scene. This will be a monumental task for the IC: People will be running all over trying to help, people will be digging in the trench, and maybe even heavy machinery might be working in the trench trying to uncover a victim. No one should be working in or around the trench without the trench’s being adequately shored. It will be difficult to remove coworkers from the location where the victim may be buried. Precautions, however, are necessary to ensure that there will be no additional victims because of secondary collapses. Therefore, all personnel working around the trench area must be cleared, and all equipment working on-scene should be shut down and locked out to minimize vibration around the collapse.
After the collapse area has been cleared, a Personnel Accountability Report should be taken to verify who is on-scene and to confirm the number of victims. Responders should ask the site foreman how many workers were on-site; those who are accounted for; and what the workers, including the victims, were doing prior to the collapse.
In addition to the technical rescue team, advanced life support resources and law enforcement should be called to the scene. The police response is necessary to help control the scene. Also, if there is a fatality, the area then becomes a crime scene and the jurisdiction of the police department. Medical care should also be on-scene early to administer to the victim during the rescue operation and help minimize the severity of the injuries associated with trench collapses.
After the trench area has been evacuated, establish a hot zone for operations. All unnecessary personnel should be at least 100 feet from the trench. Next, determine the location of the sole entry point to the hot zone for the operation. No other entry point should be allowed for the duration of the rescue.
After the scene has been cleared, the spoil pile can be moved away from the lip of the trench. Workers should start from the back of the spoil pile. While the pile is being moved, responders can collect vital information such as the type of soil involved in the collapse. Soil can be categorized as follows:
- Type A has an unconfined compressive strength of 1.5 tons per square foot or greater. This soil type is very cohesive and will hold together well when compressed. Examples of Class A soil are clay, silty clay, caliche, and clay loam.
- Type B has an unconfined compressive strength greater than 0.5 tons per square foot but is less than 1.5 tons per square foot. It is a wet, saturated soil that may show water seeping from the trench walls. Examples of Class B soil include silty loam, sandy loam, and sandy clay loam.
- Type C has an unconfined compressive strength of 0.5 tons or less per square foot. It is a very loose, free-flowing soil, similar to sugar sand; it can be the most difficult to stabilize. Examples of Class C soil include sand, loamy sand, and submerged soil.
To identify the soil type, you can perform two simple field tests, a Plasticity Test and a Thumb Penetration Test.
Plasticity Test. Take a handful of soil from the top of the spoil pile, which would represent the soil at the bottom of the trench. Also, take a handful of soil from the bottom of the spoil pile, which will represent the soil type at the top of the trench. With the soil samples in hand, try to roll out the soil sample into threads as thin as 1/8-inch in diameter. If the soil sample can be rolled into threads as long as two inches, the soil is considered cohesive.
Thumb Penetration Test. Take a sample from the spoil pile, compact it as if making a snowball, and try to indent it by pushing into the sample with your thumb. In Type A soils, it would take effort to cause an indent. In Type B soils, an indentation could be made, but the soil sample would be saturated and may or may not remain cohesive. In Type C soils, your thumb can easily penetrate several inches, and the soil can be molded easily with light finger pressure.
OTHER SIZE-UP FACTORS
In addition to soil identification, other important size-up factors must be determined. Approach the trench from the end, which is more stable than the side, and put down ground pads (four-foot 2 eight-foot 2 3/4-inch plywood) around the trench lip. These pads will help distribute responders’ weight while they are working around the collapse. These pads should also travel back from the trench lip a distance equal to the depth of the trench. Once near the trench, try to determine the following:
- The number of victims involved in the collapse. If the victim is covered, look for victim locators or clues—such as a grease can and a brush used for sealing pipe joints, a hard hat, a lunch box, or tools—that might indicate where the victim might be buried.
- If a victim is visible, establish a line of communication with him. Try to find out the nature of the entrapment, any obvious injuries or disabilities that will require immediate attention, and any information about possible additional victims who may not be visible. If the victim is physically able, supply him with a digging tool so he can help with his rescue from within the trench until the rescuers can safely enter.
- Place an atmospheric monitoring device in the trench to identify the presence of any flammable or hazardous materials, such as methane gas, that may be in the trench.
- If the monitoring device doesn’t reveal any flammability issues, ventilation in the trench can begin, as long it will not increase the potential for fire or explosion.
- Assess for any entrapment problems, other than soil, that may compromise removing the victim from the trench. Large rocks, utility materials, and sewer pipes could fall in the trench, further entrapping the victim.
- Determine the dimensions (length, width, and depth) of the trench before and after the collapse.
- Are there any utility hazards? Notify the respective utility authority of the collapse so it can send resources to help you deal with the service in the trench.
- Remove any vibration hazard in the vicinity of the trench. Shut down heavy machinery used to dig the trench. It may also become necessary to divert traffic from the scene and even shut down railroad service in the area if the tracks are in close proximity to the collapse zone.
- Identify the type of collapse. Some common types include the following:
 (4) After ground pads are in place, crews perform air sampling to check for hazards in the atmosphere. |
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 (5) After atmospheric testing is complete, ventilation equipment is put in place so fresh air can be pumped into the trench. |
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 (6) Victim locators are important clues for determining where the victim may be located. Note the helmet; it gives the rescuers a starting point for the operation. |
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—Spoil pile slide: the spoil pile is placed too close to the lip of the trench and falls back into the trench, or it can be knocked back in the trench by the machine operator.
—Sidewall shear: a portion of the trench wall shears off and falls into the trench; this happens when a trench is open for a long time and loses some of its cohesiveness.
—Slough-in: the belly of the trench wall collapses under the lip, which leaves the lip hanging over the trench.
—Lip-in: workers or equipment are working next to or on top of the lip and collapse into the trench.
This information, gathered through an effective initial size-up, can help save the rescue team vital time when it arrives. On arrival, the rescue officer of the technical rescue team is responsible for performing a thorough size-up to determine the best plan for rescuing the victim. However, since the first-arriving companies obtained this information before the rescue team’s arrival and restored order to the scene, the rescue team can immediately begin to stabilize the trench and prepare to remove the victim.
MICHAEL DALEY, a 17-year veteran of the fire service, is a lieutenant/training officer with Monroe Township (NJ) Fire District #3 and an instructor with the Middlesex County (NJ) Fire Academy, where he is responsible for rescue curriculum development. He is also a rescue specialist with New Jersey Task Force 1-Urban Search and Rescue. Daley is an FDIC and FDIC West H.O.T. instructor.
