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According to the National Institute for Occupational Safety and Health (NIOSH), on average, around 35 workers die each year as a result of trench cave-ins or similar excavation-type accidents. Additionally, excavation activities cause many worker injuries on construction sites and other industrial workplaces throughout the US each year. Being aware of the inherent risks and the preventative measures can be a matter of life and death. Our construction accident lawyers understand the causes, risk factors, and possible solutions to this problem to help keep workers safe.
Causes of Excavation & Trench Accidents
Trenching is sometimes necessary on a job site. A trench is a narrow excavation where the depth of the ditch is more profound than the width, usually not extending more than 15 feet wide at the bottom. Excavations can be any man-made cut, trench, cavity, or depression in the Earth’s surface that is formed by the organized removal of earth.
Before digging can begin on a trench, a survey must be conducted to assess the location of any water, sewer, power, Internet, or other communications lines, as well as any underground piping or other services.
If a proper survey is not done, this may lead to a cave-in once digging begins, as service lines may be unintentionally disrupted, loosening the earth and causing it to cave in.
By far, the most common reason a trench caves in is due to soil sliding. This is caused by pressure on the surrounding soil combined with excessive vibrations in the area, typically due to heavy materials or equipment being used in or around the trench.
Heavy machinery and equipment, such as excavators, jackhammers, or even shoveling, can contribute to or directly cause cave-ins.
Water is another potential contributing factor to erosion and soil slides, mainly if trenches are excavated below the water table in sandy soils or soft clay or clay-like earth. Sudden weather changes can also cause pressure on the trench or change the pressure being exerted, potentially causing or contributing to a cave-in.
This is usually the case after a rainstorm or other dramatic weather change, such as freezing and thawing, or after hazards like tornadoes or other severe storms.
Risk Factors
Soil Conditions of the Trench
Depending on its composition and current or recent weather conditions, soil may contribute to a cave-in.
- Clay: Clay is soil that is very finely grained. Rainfall will generally collect on the surface and evaporate rather than absorb into the soil. However, water that has already penetrated the clay may contribute to a cave-in. Specifically, water that causes cracks or freezes and leads to separation may contribute to trench cave-ins or soil erosion.
- Sand: Sand is granular soil, but not as fine as clay. Sandy soil usually has large pores, allowing groundwater to be absorbed. When digging trenches in sand, soil erosion and sliding pose a serious risk, as sand typically lacks integrity under even moderate construction conditions.
- Silt: Silt has soil properties that combine various aspects of both clay and sand. It’s the most sensitive to moisture, but crumbles when dry. For this reason, it presents one of the most significant challenges to digging and is a major risk factor for cave-ins.
Excavation and Digging Risks
When trenches are dug more than 5 feet deep, the risk of a cave-in increases. Trenches deeper than 20 feet require professionally engineered solutions to prevent cave-ins.
Heavy equipment that is near a digging site should be kept clear of trenches. Workers and engineers should identify any sources that might negatively affect the stability or integrity of the trench before entering or working on it.
Excavated soils must be kept at least 2 feet away from the trench edges, and a test for atmospheric hazards should be done to avoid toxic fumes and gases when digging more than 4 feet into the ground.
Workers should never work under suspended or raised loads or materials, and never follow a rainstorm until the trench has been verified safe. Trenches that have not been inspected should be considered inherently dangerous and unsuitable for working in.
Lack of Personal Protection
When working in trenches, personal protection usually means either safety harnesses or engineered safety and retaining walls designed to withstand potential cave-ins. A lack of these measures could result in serious injury or death.
When these are not used, or when the retaining walls are not sufficient to protect against a cave-in, workers may be seriously injured or die.
Prevention and Practical Solutions
Prevention is accomplished through a combination of safety and preparedness protocols. One way to prevent a cave-in is an excavation technique called “shoring” or “sloping.”
Shoring
Sloping methods require workers to dig a trench with an angled entry and angled sidewalls. This is not always possible on every job site, as it may interfere with the project, damage adjacent buildings, or render equipment unusable.
When sloping is used, soil is placed 2 feet or more from the edge of the trench to prevent it from falling back into the trench while workers are working.
Hydraulic Shoring
Shoring is a process in which posts, wales, or struts are used to hold back the soil in a trench. Today, hydraulic shoring techniques are commonly used on-site. These techniques utilize a prefabricated strut or wale made of aluminum or steel. They’re light enough to be installed by one worker. They’re gauge-regulated so that pressure from the soil is evenly distributed along the trench line, and the side of the strut or wale facing the trench can be pre-loaded to take advantage of a soil’s natural cohesion – resisting soil movement or sliding. Finally, they can be adjusted to an almost unlimited range of depths and widths.
Pneumatic Shoring
An alternative to hydraulic shoring is pneumatic shoring. This process is similar to hydraulic shoring, except that pneumatic shoring uses air pressure rather than hydraulic pressure. There is an increased risk with this type of structure, however, because the worker must be in the trench when adjusting the struts.
Screw Jacks and Trench Boxes
Screw jacks differ between hydraulic and pneumatic systems in that they must be adjusted manually. When these are used, there is a significant risk to the worker since he must be in the trench to adapt them.
Single-cylinder hydraulic shores are typically used in water systems, where stability is paramount. Underpinning is a process of engineering a foundation and other structures for the trench, using it to stabilize retaining walls.
Trench boxes take an entirely different approach to prevention. Instead of shoring, they are intended to prevent cave-ins or soil slides. The space between the trench boxes (the side walls) is backfilled to prevent lateral movement. Struts are used to prevent soil from falling on workers.
A professional engineer must engineer trench boxes to withstand the external forces acting on them. If they fail, a cave-in will occur, which may result in serious injury or death.
Benching
Benching is a process of building what are essentially steps or a step leading down into a trench. A single bench is a single “step” that leads into a trench, which can be no more than 4 feet deep. Multiple bench setups consist of a series of steps; the first must be no deeper than 4 feet, while the remaining steps may be up to 5 feet deep.
Reducing Risk of Excavation Accidents
Companies concerned with the risk of cave-ins can also reduce the risk of this occurring by removing surface debris near the trench that could be hazardous, checking weather conditions before the construction project, as well as during each day of the project, and ensuring that workers are not working on job sites where rain or ice has compromised the integrity of shoring attempts or trench boxes.
Companies should examine the particle size of excavated soil to ensure it holds together before building trench boxes or digging, and they should also look for signs of disturbed soil from previous construction projects.
Consider normal vibration in the area, plus any introduced on the job site by construction equipment. Make sure that adjacent structures are stable, that workers have safe passage for entry and exit from the trench, and that an emergency response plan is in place should an accident occur.
Education and Training
Employees should be trained and educated about the risks of the job site. A designated “competent person” should be appointed to oversee the safety measures at the job site. Utility lines should be marked before digging.
A competent person, acting as a safety officer, should evaluate the soil to determine its stability. If necessary, an engineer should be brought in for further analysis. Soil conditions can change dramatically within days, so this process should be repeated every day, especially if humidity or moisture levels change.
The job site should have designated “safe locations” that are away from the trench and spoil piles for heavy equipment routes.
If trenches are more than 20 feet deep, employees should be educated about the inherent risks of trench boxes and designs intended to hold back earth in the trench. Additionally, engineered solutions should be employed to reduce the risk to all workers in the trench.
For example, workers should be made aware that engineered solutions may provide additional safety; however, trench boxes, struts, and other safety devices are not fail-safe.
A trench emergency plan should outline the steps to take in the event of an emergency. The safety officer should inspect the excavation, adjacent areas, and any protective systems used on the site every day before work begins. Workers should not be asked to work before this safety inspection.
Subcontractors who do not work for the company should be given training during orientation when they arrive on site.
Any ladders used should never be more than 25 feet from any worker in the trench. This is primarily for safety. If a worker must leave the trench quickly, the ladder is usually the only means of escape. Having it near the worker minimizes the risk that he or she will be caught in a landslide/soil slide or cave-in.
Protection and More Resources
Workers should always wear all assigned protective gear. This may include, but is not limited to, safety goggles, protective equipment and reflective gear, hard hats, gloves, respiratory gear, and durable boots with steel toe linings. When possible, personal rigs should be worn to facilitate a quick evacuation from a trench.
When a Cave-In Occurs
When a cave-in does occur, options may be limited, depending on where it happens and the nature of the soil. If a cave-in occurs, there should be protocols in place to call emergency personnel so they can help rescue trapped individuals. Rescue personnel include emergency services, fire and rescue, and, if applicable, local police.
In some situations, it may be possible to excavate the individual to safety, either by digging or by removing soil from the side of the trench to allow for a secondary cave-in away from the individual.
These methods are hazardous and may result in further injury or the death of the individuals trapped. Therefore, the safety protocol should be strictly followed in emergencies. If it does not allow for further excavation, do not excavate. In some situations, it may put more workers in danger.
There are many situations where a cave-in results in death, either immediately or within seconds or minutes, and there is no practical way to save the individuals who are trapped. This is why prevention is so crucial in trenching and excavation.
If you’ve been injured on a construction site or if you feel a site you are currently working on is unsafe, don’t hesitate to contact a lawyer and discuss the situation. You have rights, and you shouldn’t be afraid to assert them.
Additional References
Information For The Landscaping Profession
OSHA: Trenches and Excavations