Trenches are long, narrow tunnels in the earth dug out by heavy machinery. Many construction sites and other workplaces use trenches for building foundations or tunnel construction. Workers also use them to install or repair utility lines below the ground or other jobs requiring underground access. They differ from other tunnels in that their depth needs to be at least as long as their width.

Trenches are highly useful and versatile, but they can be hazardous for construction workers due to the risk of collapse. There are many reasons a trench might cave in, but the event can cause severe injury or even death for workers.

Because of the potential tragedies, following proper safety procedures is essential for trench work. Employers and employees are responsible for doing whatever they can to prevent possible collapses. Here’s more about what causes a trench to collapse and how to avoid these occurrences.

How Trenches Collapse

Trench collapse might occur due to a variety of reasons. Anything from the soil’s texture to outside disturbances might cause the tunnel to give. The dirt falls in very quickly, so it’s difficult to stop a collapse once it starts. The swiftness is another reason why preventive measures are so critical for trench work.

Here are some common reasons for trench collapses:

  • Too much pressure: A frequent cause of cave-ins is when heavy equipment places too much pressure on the soil. Because the machinery digs out most of the earth, it becomes quite hollow. The pressure on the trench walls becomes too intense, and the tunnel gives in.
  • Incorrect sloping: When a trench isn’t correctly sloped, it becomes unstable and maybe even unable to support the weight of workers. This danger is why following proper sloping measures is essential for worker safety.
  • Flooding: Excess amounts of water flowing through a trench causes soil instability. The walls could collapse, and the tunnel might give in entirely. Other weather events, such as snowstorms or droughts, might cause breakdowns. If any water accumulates within the trench, workers must not enter without proper safety equipment. Ideally, inspectors should remove all water buildup before workers enter.
  • Unstable soil: During the excavation of the trench, the earth might be improperly or unevenly packed. Checking the soil packing before and during trench work prevents this in most cases.
  • Nearby disturbances: Outside vibrations, like nearby construction work or other loud equipment, might shake the dirt until it gives in.
  • Neglect: In some cases, employers and workers don’t take the trench’s proper precautions and preventive measures. If inspectors don’t complete regular check-ins of the tunnel itself and surrounding areas, they might miss potential problems.

A large amount of soil might weigh as much as a car. Collapses might cause other hazards, such as falling equipment. Because of the severe dangers, all employees need to follow the proper safety protocols to prevent trench collapse. If not, workers might sustain serious injuries such as:

  • Broken bones.
  • Brain damage or head trauma.
  • Exposure to harmful gases.

In severe cases, some workers even face death by suffocation.

12 Ways to Keep Trenches From Collapsing

Preventive collapse measures are imperative for worker safety. You can take many precautionary measures to prevent a trench collapse. These precautions occur both before and while completing trench work:

  • Before: These are any preventive measures completed before workers enter the trench. These might include inspecting the area before construction and installing protective systems.
  • During: These are ways workers can reduce collapses while below ground. That might look like following safety procedures or reporting any noticeable issues with safety structures.

If you’re wondering how to avoid a trench collapse, here are some actions to prevent these incidents.

Ways to Prevent Collapses Before Trench Work

The time before construction work begins is critical for safety. A thorough pre-check might mean the difference between a successful job and an injured worker.

These are critical ways to stop potential cave-ins:

  1. Analyzing the area beforehand: Workers must study the terrain around the intended trench site before starting work. They should account for all existing utility lines and avoid them. Crews can call the number 811 to alert utility companies and ask to have the lines marked. Designers should note surrounding structures that might cause a collapse, such as other construction sites or heavy traffic.
  2. Inspecting soil: According to OSHA regulations, every soil classification has different sloping and design requirements. Designers and engineers should study the ground and designate a soil type before beginning to dig. OSHA defines the separate soil types as Type A, Type B and Type C. Type A soil is solid and packed together, such as clay. Type B soil might contain fissures or breaks but remains mostly packed. Type C soil is typically granular and looser than the other types. Inspectors use the soil type to determine the trench’s slope and depth.
  3. Sloping: Sloping is an essential part of trench work. It consists of digging the canal walls at angles so the soil’s weight rests away from trench workers. After completing the slope, the tunnel will have a funnel shape. Sloping ensures heavy amounts of earth don’t sit above workers’ heads. In addition, workers push any extra dirt away from the trench to reduce the risk of collapse further.
  4. Shoring: Shoring is another practice that prevents collapses. During this process, construction workers place metal plates on both sides of the trench. These plates keep the soil in place by matching width and height.
  5. Shielding and boxing: Typically made of steel, these four-walled boxes or shields protect workers during trench work. The box walls stabilize the trench and keep the walls from falling in. They are portable and easily moved into the trench. Professional engineers must approve shield boxes before use.
  6. Watching the weather: Adverse weather conditions, like excess rainfall or snow, might weaken trench walls and compel them to fall in. Employers should never make workers enter the trench during heavy rain or other poor weather conditions.

Ways to Prevent Collapses During Trench Work

Employers, engineers and workers can also stop collapses from occurring while trench work is underway. Daily inspections allow workers to assess the trench’s safety and ensure collapses won’t easily happen:

  1. Checking the area at the start of each shift: Responsible persons should complete a daily inspection of the trench site before workers enter the tunnel. Inspectors should study protective systems like shields and slopes to ensure correct functioning. They should also check any adjacent areas for possible hazards. Inspectors must inspect the soil quality and ensure it’s stable enough for work. If recent disasters or storms have torn through the area, they study the entire site. Supervisors also complete other inspections during daily work as needed.
  2. Testing for atmospheric issues: Before and while workers are in the trench, inspectors should test the atmospheric conditions. Because trenches are below the ground, oxygen levels and atmospheric pressures are unstable. Sites could also contain toxic gases or fumes that harm employees. If the air presents hazards, employers must take the necessary measures to bring them back to safe levels. In addition, all trench workers must have respirational masks and tools to stay safe while below ground.
  3. Keeping heavy equipment away from edges: Supervisors must monitor heavy equipment on-site while workers are in the trench. Construction machinery must be kept away from trench edges to reduce potential accidents.
  4. Using a warning system: Warning systems can alert workers to potential dangers while in the trench. These systems might consist of hand signals, loud sirens or other signs that let workers know the whereabouts of equipment and other essentials.
  5. Ensuring workers all follow standards: Worker safety begins with the right education. Employers should begin each shift by explaining the duties for the day and any potential dangers. Before entering the trench, workers need to memorize Occupational Safety and Health Administration (OSHA) standards and other workplace rules for their job. The employers are responsible for enforcing these rules, just as the workers must listen and follow the standards. By abiding by all the procedures, teams can avoid collapses.
  6. Checking equipment regularly: After each use, employers should closely inspect all pieces of equipment. They must address any potential cracks or failures in the equipment. Supervisors should also ensure construction equipment operators are fully trained and certified to handle the machinery safely.

OSHA Trenching Requirements

OSHA ensures safe working conditions for all employees by creating workplace standards. For construction workers, OSHA outlined safety precautions so workplaces respect their safety. Hazardous work conditions put the lives of workers in danger.

OSHA created a set of standards for trenching and excavation, and they became law in 1989. These documents outlined the safety regulations all trench sites must follow during work. From required personnel to precautionary measures, the standards thoroughly outline trenching requirements.

Here are some of the key OSHA trenching regulations:


OSHA standards state every trench site must have specific staff members to ensure safety. Each member has a particular role that helps with the well-being of the entire team. When crews follow their responsibilities, they reduce the number of accidents and hazards.

Here are some of the roles:

  • Competent person: This individual is responsible for identifying potential safety hazards on the site. They also take the necessary measures to get rid of the risks. If they find an unsafe aspect, they have the right to halt construction work until they resolve it. Typical tasks for a competent person include inspecting soil quality, designing safety structures like ramps, monitoring equipment and conducting inspections.
  • Professional engineer: This engineer is responsible for developing and maintaining more complicated trench designs. Some of the day-to-day duties of the professional engineer include approving new safety systems, designing precautionary measures and advising employers on how to use complex trenching systems.
  • Employer: The employer oversees the daily operations of trench workers and is ultimately responsible for their safety. They ensure all employees follow OSHA safety standards and inspect safety structures at the site.
  • Worker: Trench workers complete their daily work while also following safety guidelines. They look out for fellow employees and have a duty to follow all safety instructions.

Sloping Requirements

OSHA also outlines sloping guidelines for trenches. The angled nature of slopes could be hazardous if not constructed correctly. OSHA designates a maximum allowable slope, which is the steepest acceptable angle for the slope while still safe.

These are OSHA’s sloping guidelines:

  • Approval by professional engineer: The engineer must approve all sloping and benching systems before being created. The engineer or designer must write this information, and employers must have it on hand during the construction of the sloping system.
  • No steeper than 1.5:1: For trenches with heights of 20 feet, the slope angle cannot be steeper than 1.5:1. In other words, for every foot of depth, the trench needs to be sloped back by 1.5 feet. This structure is safe for any soil.
  • Sloping requirements vary by soil type: Professionals classify trench soil by Type A, Type B and Type C. Before designing the slope system, a competent person or professional engineer should examine the soil. Maximum slope allowances vary by soil type.

Other OSHA Standards

OSHA has several other regulations for trenching. By following these procedures, employers and workers can prevent collapses and other accidents.

Here are a few more standards for trenching sites:

  • Protective equipment: All employers must supply protective equipment for all workers. Some examples include a lifeline and harness, bright apparel visible to nearby traffic, hard hats, durable gloves and respirators. Employees must wear these protective pieces at all times while in the trench.
  • Access and egress: OSHA requires employers to supply certain equipment like steps, ramps and ladders for trench sites. All of these pieces must be easily accessible and designed so workers don’t have to move more than a few feet once in the cavern. The equipment is essential for quick exits from the tunnel.
  • Site inspections: Each day, the competent person must inspect trenches, protective systems and nearby areas to ensure safety. If the inspector finds any unsafe conditions, they halt work until they can resolve the issues.
  • Engineer approval of site: Professional engineers must approve any trench sites that pose potential hazards to workers. If the sites are not on stable rock or are below the foundation, an engineer must study the area and approve it before digging can commence.

Contact NASP for Trenching and Evacuation Safety Training

The National Association of Safety Professionals commits to providing safety professionals with intensive training. We understand how critical safety is in construction workplaces. Our team works hard to offer professional certificates and programs that create confident, competent employees. NASP differentiates ourselves from other professional training programs with our innovative training strategies. We emphasize andragogical methods that encourage student interactions. Our construction courses are thorough and dynamic, preparing you for the site.

Our Trenching and Excavation course prepares students for all aspects of trench work. You learn critical skills in site analysis, soil classification and prevention of collapses. With our competitive pricing and dynamic lessons, we provide a high-quality experience.

Purchase our training course today or contact NASP to learn more about trench safety training.

About the Author


Pete Nemmers

Pete Nemmers serves as NASP’s Director of Training Development, bringing a wealth of expertise to the organization. With a background rooted in safety and training, Pete plays a pivotal role in shaping the training programs offered by NASP. Pete ensures that NASP remains at the forefront of safety education, equipping professionals with the knowledge and skills necessary to navigate and excel in the dynamic field of safety.
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