Trenching & Excavation: Safety Hazards & Control Measures
Introduction to Trenching and Excavation
Working in and around trenches and excavations can be dangerous. Collapses can happen suddenly and without warning, burying workers alive beneath tons of soil. According to the U.S. Department of Labor’s Occupational Safety and Health Administration (OSHA), trenching and excavation cave-ins kill an average of two dozen workers annually in the United States.
Most trenching and excavation accidents are preventable if workers and employers follow safety rules and regulations. OSHA’s trenching and excavating standards (29 CFR 1926.650 – 656) are designed to protect workers by requiring that excavations be properly shored, sloped, or benched, depending on their depth that protective systems be used when needed.
Excavation vs. Trenching
The terms “excavation” and “trenching” are often used interchangeably, but there is a difference. An excavation is any man-made cut, cavity, trench, or depression in the earth’s surface formed by earth removal. A trench is a narrow excavation made below the surface of the ground.
Trenches are most often used to install utility lines or drains. They may be only a few inches wide and a few feet deep or much larger. Deep trenches, over 20 feet deep, are particularly dangerous because of the increased risk of collapse.
What is Excavation for OSHA?
An excavation is any man-made cut, cavity, trench, or depression in the earth’s surface formed by earth removal. A trench is a narrow excavation (in width) made below the ground’s surface. Excavations are classified according to their purpose:
- Foundation excavations are for footings and basements.
- Utility excavations are for sewers, water mains, gas lines, and other underground installations.
- Highway and road excavations are made for grading, drainage, and subbase preparation.
- Canal and ditch excavations are used for irrigation, drainage, and sewage disposal.
- Surface mining excavations are made in strip mining, open-pit mining, and quarrying.
What is Trenching for OSHA?
Trenching is defined as digging a narrow hole (in width) below the ground’s surface. The depth of a trench may vary, but most trenches are less than 15 feet deep. A ditch is defined as a trench that is greater than 15 feet in depth.
What Are The Soil Classification Categories?
There are four soil classification categories, with Type C being the least stable and Type-A the most stable:
- Type A – Soil that is cohesionless and inorganic. Includes gravel, sand, silt, or clay, free of organic matter. This soil has a high probability of caving. Protective systems must be used at all times.
- Type B – Soil that is cohesionless and inorganic with some organic matter. Includes gravel, sand, silt,, or clay with up to 12% organic matter by weight. This soil has a moderate probability of caving. Protective systems may be used when excavating 6 feet (1.8 m) or less below the ground surface.
- Type C is cohesionless and inorganic soil with a high organic matter content. Includes gravel, sand, silt, or clay with more than 12% organic matter by weight. This soil has a low probability of caving. Protective systems are not required when excavating 6 feet (1.8 m) or less below the ground surface.
- Type D – Soil that is cohesionless with a high organic matter content. Includes gravel, sand, silt, or clay with more than 50% organic matter by weight. This soil has a very low probability of caving. Protective systems are not required when excavating any depth below the ground surface.
Different Methods Of Excavation
The three most common methods of excavation are hand excavation, machine excavation, and blasting.
- Hand Excavation – The least mechanized method of excavation, hand excavation is typically used for small projects or areas where machinery is impractical. Hand excavations can be done with various tools, including shovels, picks, and mattocks.
- Machine Excavation – Machine excavation uses powered machines to excavate an area. Common types of machine excavation include backhoes, Bulldozers, and front-end loaders.
- Blasting – Blasting is an excavation method involving using explosives to break up rock or soil. This method is typically used in mining and quarrying operations.
Different Types Of Trenching
The three most common types of trenching are open-cut, pipe jacking, and box culvert.
- Open Cut – Open cut is the most common type of trenching. It is used to excavate an area to install utilities, such as sewer and water lines.
- Pipe Jacking – Pipe jacking is a type of trenching used to install underground pipes. It involves boring a hole through the earth and then jacking the pipe into place.
- Box Culvert – A box culvert is a trench used to install drainage or sewer pipes. It involves digging a rectangular hole and then installing the pipe in the hole.
What is a competent person?
A competent person is an individual, designated by the employer, capable of identifying existing and predictable hazards in the surroundings or working conditions that are unsanitary, hazardous, or dangerous to workers, and authorized to take prompt corrective measures to eliminate them.
Under the Excavation standards, tasks performed by the competent person include:
- Classifying soil;
- Inspecting protective systems;
- Designing structural ramps;
- Monitoring water removal equipment; and
- Conducting site inspections.
Factors To Consider When Bidding on a Job
Before preparing a bid, employers should know as much as possible about the Jobsite and the materials they will need to have on hand to perform the work safely and in compliance with OSHA standards. A safety checklist may prove helpful when employers are considering new projects. Factors to consider may include:
- Proximity and physical condition of nearby structures
- Soil classification
- Surface and groundwater
- Location of the water table
- Overhead and underground utilities
- Quantity of shoring or protective systems that may be required
- Fall protection needs
- Number of ladders that may be needed
- Other equipment needs.
Employers can gather the necessary information through Jobsite studies, observations, test borings for soil type or conditions, and consultations with local officials and utility companies. This information will help employers determine the amount, kind, and cost of safety equipment to perform the work safely.
Hazards Associated With Excavation
There are a total of seven deaths each year due to work in excavations, with many more people sustaining serious injuries. Collapsing soil can be an unpredictable phenomenon that threatens both workers and members of the public at large; these accidents typically happen when there’s no warning sign – shallow workings seem most prone (and dangerous) for this type of collapse because it occurs suddenly without any prior indication such as cracks appearing on ground surfaces or walls caving inward before their time!
The specific hazards associated with excavations are as follows:
Collapse Of The Sides
One of the major hazards of excavation is the collapse of the sides. If the sides of the excavation site collapse, it can be extremely dangerous for workers. In some cases, it can even lead to fatalities.
Materials Falling On Workers In The Excavation
Materials falling on workers in the excavation can pose a serious safety hazard. Even a small object falling from a great height can cause serious damage. That’s why it’s important for workers to wear proper safety gear and be aware of their surroundings.
Falls Of People And/Or Vehicles Into The Excavation
Falls of people and/or vehicles into the excavation can be extremely dangerous. If a worker falls into an excavation, it can be difficult for them to get out. And if a vehicle falls into an excavation, it can crush workers who are in the area.
Workers Being Struck By Plant Or Machinery
Another hazard of excavation is workers being struck by plants or machinery. This can happen if a piece of equipment falls into the excavation or a worker is in the way of a moving piece.
Exposure To Hazardous Substances
Excavation work can also expose workers to hazardous substances, such as asbestos. Asbestos is a type of mineral that is known to cause cancer. If workers are exposed to asbestos, it can be extremely dangerous.
Working In Confined Spaces
Another hazard of excavation work is working in confined spaces. This can be extremely dangerous because there is a risk of being trapped if the sides of the excavation collapse.
Injuries Associated With Excavation
There are a variety of injuries that can be associated with excavation work. These injuries include:
- Cuts And Bruises: Cuts and bruises are common injuries that can occur during excavation work. If workers are not careful, they can cut themselves on sharp objects or bruise themselves on heavy equipment.
- Sprains And Strains: Sprains and strains are common injuries that can occur during excavation. Workers lifting heavy objects or twisting their bodies in awkward positions can strain their muscles and ligaments.
- Fractures: Fractures are another type of injury that can occur during excavation work. If workers fall from a great height or are struck by heavy objects, they can break their bones.
- Head Injuries: Head injuries are also common in excavation work. If workers are struck by falling objects or if they fall from a great height, they can sustain serious head injuries.
- Spinal Cord Injuries: Spinal cord injuries are another type of injury that can occur during excavation work. If workers fall from a great height or are struck by heavy objects, they can damage their spinal cord.
- Death: In some cases, excavation work can lead to death. If workers are buried alive in a collapse or if they are struck by heavy machinery, they can be killed.
Specialist Equipment, Such As Pneumatic Drills
Specialist equipment such as pneumatic drills, jackhammers, and trenchers may be used in excavation work. This type of equipment can be extremely dangerous if it is not used properly.
Influx Of Ground Or Surface Water And Entrapment In Silt Or Mud
An influx of ground or surface water into an excavation can cause workers to be trapped in silt or mud. This can be extremely dangerous because they may not be able to breathe.
Working In Extreme Weather Conditions
Excavation work can also be hazardous in extreme weather conditions. If workers are working in hot weather, they may be at risk of dehydration. And if workers are working in cold weather, they may be at risk of frostbite.
Proximity Of Stored Materials, Waste Materials, Or Plant
To The Excavation If materials, waste materials, or plants are stored too close to the excavation, they may fall into the excavation and cause injury to workers.
Contact With Underground Services
Contact with underground services such as water, gas, and electricity can also be hazardous. If workers damage these services, they may cause an explosion or a fire.
Soil Erosion And Slope Instability
If the soil around an excavation is not stable, it may collapse into the excavation. This can be extremely dangerous for workers who are inside the excavation.
One of the most dangerous hazards of excavation work is trench collapse. If the sides of a trench collapse, workers can be buried alive.
Access And Egress To The Excavation
Another hazard of excavation work is access and egress to the excavation. If workers have to climb down into an excavation, they may fall and injure themselves. And if workers have to climb out of the excavation, they may also fall and injure themselves.
Fumes, Lack Of Oxygen, and Other Health Hazards
Excavation work can also be hazardous to workers’ health. If workers are exposed to fumes, they may become ill. And if the excavation is not properly ventilated, workers may be at risk of Suffocation.
Repetitive Motion Injuries
Repetitive motion injuries are also common in excavation work. If workers perform the same task over and over again, they can strain their muscles and ligaments.
If workers are working in an area where asbestos is present, they may be at risk of exposure to the deadly fibers.
If workers are working in an area where lead is present, they may be at risk of exposure to the toxic metal.
Working at Night
Excavation work can also be hazardous if it is done at night. If workers are working in an area where there is poor lighting, they may be at risk of injury.
Precautions and Controls Measures For Excavations
The following precautions and controls should be adopted:
- The person in charge of an excavation must always be conscious of their safety and well-being and those around them. They need clear instructions on how to work safely within a construction site so that no one gets hurt or killed during this process which can take hours, depending upon what needs to be done!
- The sides of the excavation must be shored up to prevent them from caving in and falling on top of the workmen. For very moist soils, stakes can also act as a protective barrier against falls by securing one side while leaving another exposed at just enough spots so that it doesn’t cause too much trouble when removed later during construction-a technique known respectively as “digging for stability.”
- To protect themselves, the workers should always wear hard hats during excavation. It’s essential to wear a hard hat if you’re around falling debris or working with heavy machinery.
- If you’re digging 2 meters or deeper, it’s best practice to provide guard rails and toe boards around the surface of your working area.
- When excavating, it is essential to take steps to prevent vehicles from getting too close to the edge of the excavation. Warning signs and barriers can help keep vehicles away from the edge. If a vehicle tips materials into the excavation, stop blocks should be placed behind its wheels. These safety measures can help prevent accidents and injuries.
- Darkness can be a detriment to any excavation site. That is why it is of the utmost importance that the area is well-lit at night, not only for the safety of the workers but also to deter potential vandals or looters.
- All plant and equipment operators must have a strong knowledge of how to safely move their pieces around, but non-operators should stay away from any moving parts.
- Operators of the noisy plants must wear PPE during excavation. This is to protect them from harmful noise levels. PPE includes earplugs or earmuffs, as well as other protective gear.
- If you are planning to excavate on or near a property, it is essential to take measures to ensure the structure’s safety. This may include shoring up nearby buildings and installing scaffolding. Excavation trenches can also destabilize neighboring structures, so it is essential to be aware of this when planning your work.
- Excavation work can pose a serious risk of flooding if not properly controlled. To minimize the risk of flooding, excavations must be adequately drained, and pumps must be used to remove any accumulated water. Additionally, the main water supply should be isolated to prevent any uncontrolled influx of water. By taking these precautions, the risk of flooding can be significantly reduced.
- One of the most important aspects of excavation safety is controlling exhaust fumes. Plants such as petrol or diesel generators should not be located near the top of the excavation, as exhaust fumes can be dangerous. Instead, place them at the bottom of the excavation or where they will not ventilate directly into the work area. In addition, make sure that any ventilation fans are properly ventilated to the outside.
- Several things need to be considered when excavating around buried services. The first is to locate the position of the services using all available service location drawings. This will help to avoid any potential hazards. Once the position of the services has been confirmed, specific excavation safety controls should be put in place. These may include using service location equipment, installing barriers, or using protective clothing. Specific trained people should implement excavation safety controls to help avoid any potential accidents or injuries.
- When working near live electrical cables, all safety precautions must be followed. This includes the correct use of personal protective equipment (PPE), the correct use of tools, and the correct way to approach and work around the cables. It is also essential to ensure that excavated materials are correctly disposed of to not pose a hazard to people or equipment.
Three Primary Protection Methods In Excavation
Three primary protection methods are available for excavation: sloping, shoring, and shielding. Each method has its own advantages and disadvantages that must be considered when choosing the most appropriate method for a particular excavation project.
Sloping is the simplest and least expensive of the three primary protection methods. It involves excavating at an angle so that the sides of the excavation are sloped. This method is most appropriate for shallow excavations and where the soil conditions are not likely to collapse.
Shoring involves installing supports around the perimeter of the excavation. These supports can be made of wood, steel, or concrete. Shoring is more expensive than sloping, but it is more effective in preventing collapses. It is most often used for deep excavations or unstable soil conditions.
Shielding consists of installing a protective barrier around the perimeter of the excavation. This barrier can be made of wood, steel, or concrete. Shielding is the most expensive of the three primary protection methods but is the most effective in preventing collapses. It is most often used for deep excavations or where the soil conditions are very unstable.
When choosing the most appropriate protection method for an excavation project, several factors must be considered, including the excavation depth, the soil conditions, the type of material being excavated, and the budget. The most appropriate method will vary depending on the project’s specific conditions.
When employers share the details of their safety and health programs with workers, they should emphasize workers’ critical role in keeping the job site safe. Employers also need to emphasize specific practices that will help reduce the risk of on-the-job injuries at excavation sites. Such practices can include the following:
- Know where underground utilities are located before digging.
- Keep excavated soil (spoils) and other materials at least 2 feet (0.61 meters) from trench edges.
- Keep heavy equipment away from trench edges.
- Identify any equipment or activities that could affect trench stability.
- Test for atmospheric hazards such as low oxygen, hazardous fumes, and toxic gases when workers are more than 4 feet deep.
- Inspect trenches at the start of each shift.
- Inspect trenches following a rainstorm or other water intrusion.
- Inspect trenches after any occurrence that could have changed conditions in the trench.
- Do not work under suspended or raised loads and materials.
- Ensure that personnel wears high-visibility or other suitable clothing when exposed to vehicular traffic.
Employers should consider establishing and maintaining safety and health management systems that provide systematic policies, procedures, and practices for protecting workers from job-related safety and health hazards.