Trenching and Excavation Hazards

While trenches and excavations are essential for many construction processes, they also present potential hazards for workers. In 2022, 39 workers died from trench or excavation-related accidents. Trenches are challenging to access, and they face the risk of collapse. They might also contain hazardous atmospheric conditions. Understand more dangers associated with trenching and excavation to prepare for them properly.

What Is the Difference Between Trenching and Excavation?

The Occupational Health and Safety Administration defines excavations as any human-made cut, cavity, trench, or depression formed by earth removal. Meanwhile, they describe a trench as a narrow excavation below the ground. Generally, a trench is deeper than its width, which is no more than 15 feet wide.

Excavation and Trenching Hazards

Trenching excavations allow construction workers to access underground areas. They might use trenches to lay utility lines or shape the foundation for a new building. Before workers can begin the excavation process, they must thoroughly inspect the area for potential dangers. Employees can start underground tasks after enacting the correct protective measures.

Even after thoroughly inspecting the surrounding area, excavations can present many risks to employees. A cubic yard of soil can weigh 3,000 pounds, almost as much as a car. Potential collapses or falls might lead to suffocation or death. All workers on a job site must be aware of the dangers of trenching and excavation to avoid accidents.

Here are common hazards associated with trenching and excavation jobs.

1. Collapses or Cave-ins

Cave-ins are among the riskiest problems for trench workers. During a cave-in, the walls collapse inward and the trench fails. The soil might bury, suffocate, or otherwise injure workers. People pinned underground could develop brain damage from suffocation or break limbs. Collapses are also excavation hazards that pose the most significant threat to workers’ lives.

These are some typical reasons for trench collapse.

• Unstable soil: If the soil in the trench can move around, it might cause the walls to become unstable and fall in. Sometimes, the soil is dry and doesn’t hold together correctly.
• Nearby vibrations: Depending on where builders construct the trench, heavy traffic or nearby construction might cause excess vibrations. These could shake the trench, causing the soil to fall and the tunnel to collapse.
• Adverse weather: Weather is a dramatic threat to trench stability. Flooding or heavy rainfall might cause water accumulation at the bottom of the trench and weaken the walls’ strength. According to OSHA standards, trench workers should not work in trenches with water buildup until they can properly remove it. Rain can also flood the trench and cause a collapse.
• Too much pressure: If workers remove large amounts of soil or place heavy equipment near the edge of the trench, the pressure might cause the walls to cave in. A minimum of two feet from the trench edge is required for ‘spoil’ (piles of dirt or debris from excavation).

Collapses threaten workers’ lives and undermine entire excavation projects. Teams must take precautions for cave-ins before beginning trench work. OSHA recommends sloping trench walls, shielding them with trench boxes, or shoring them to reinforce their stability.

2. Hazardous Atmospheres

Oxygen deficiencies and toxic air conditions are common below ground. Exposure to dangerous toxins might cause respiratory issues or diseases, so they present a severe danger to workers.

During daily inspections, supervisors should ensure air conditions are suitable before teams begin work. If they detect a hazardous substance or poor air quality, they should halt work until they can solve the issue. OSHA also instructs supervisors to provide workers with proper ventilation and respiratory tools.

Here are some examples of hazardous air conditions.

• Not enough oxygen: If workers don’t receive enough oxygen, they might reach an oxygen deficiency and struggle to breathe. Or, other gases and substances in the trench might replace oxygen. To maintain healthy oxygen levels, inspectors must remove any harmful toxins and require all workers to wear protective gear, like atmosphere-supplying respirators, which supply workers air from an independent source.
• Hazardous substances nearby: Some excavation sites are close to landfills or chemical plants. Contaminants like hydrogen sulfide or carbon monoxide could accrue in the trench. Emergency procedures ensure the air does not become too toxic in these cases.

According to OSHA, supervisors should test atmospheres in trenches and excavations deeper than 4 feet and there is a risk of a hazardous atmosphere. OSHA considers it immediately dangerous to life or health if oxygen levels are less than 19.5%.

3. Hitting Utility Lines

All trenches face the risk of striking underground utility lines. Before construction, engineers are responsible for detecting all nearby utility lines, but there’s always the possibility of missing one. The outcome could be dangerous if workers hit one of these lines or uncover an improperly insulated line. Damaging municipal lines is harmful to residents’ well-being and expensive to repair.

Here are examples of utility lines and the dangers they pose.

• Water: If workers strike a water line, they could cause the pipe to leak. In turn, leaks might reduce or contaminate the residents’ water supply. Workers might also encounter contaminated or toxic water. Any resulting flooding could cause a cave-in.
• Electrical: Striking an electrical line is highly dangerous for workers due to electrocution possibilities. The body goes into cardiac arrest if it comes into contact with too much electricity.
• Natural Gas: Natural gas utility lines are especially hazardous because of the high amounts of pressure used to run the gas through pipelines. Even a small encounter could cause an explosion.

Before starting excavation, supervisors should contact local utility suppliers (call 811) to see the specific locations of all the existing utility lines. Instruct workers to report any lines they discover while excavating or trenching.

4. Falling Materials

Many trenching materials on-site present a hazard to workers. Construction equipment like dump trucks or ramps are heavy and potentially dangerous for workers. Materials or equipment that sit too close to the trench’s edge could fall into the excavation.

Here are some dangers that could occur due to falling materials.

• Suffocation: If a large piece of equipment falls into the trench, it could cut off healthy oxygen flow for workers. Or, heavy loads of dirt or rocks might fill the trench and make breathing difficult. These materials can damage or block exits, trapping workers below.
• Head trauma or injury: If falling materials strike someone’s head, it could cause brain damage or head trauma. Depending on the size of the equipment and speed of the fall, workers could sustain serious and potentially fatal injuries.

Do not allow workers to be in the trench or excavation area if other workers are using digging or lifting equipment to handle loads above. Supervisors should also ensure workers stand away from equipment being unloaded or loaded because of the threat of falling materials.

You should keep materials and equipment at least 2 feet away from the trench edge and use a retaining device to keep them from falling into the excavation. Protect workers by instituting a rule that prohibits them from working on sloped faces unless the people below them have adequate protection from the hazards of falling or rolling materials or equipment.

5. Mobile Equipment on Site

Accidents from equipment on construction sites, such as dump trucks, are common. Employees operating equipment may have an obstructed view and struggle to see when approaching the trench. OSHA suggests that construction sites have a spotter or flagger to direct operators and prevent the equipment from falling into the trench.

Workers should also stand back when loading and unloading material and debris to avoid getting hit by flying debris or soil. Workers must wear protective gear such as vests that make them more visible to mobile equipment operators. Hard hats will also protect them from hazards such as falling material.

6. Flooding

A trench may flood if it is underneath the water table, near a watercourse bank, or in a location that experiences adverse weather conditions. It’s essential to have an evacuation plan if the job site floods.

Keep the water accumulation low to prevent hazards such as slips and falls and electrical equipment malfunctions. Water inside a trench can also make it challenging for workers to get out. OSHA prohibits workers from entering a trench with water in it unless there are adequate measures to protect them.

The following precautions can keep workers safe when water levels rise:

• Keep pumps on hand to use in a flood.
• Place soil heaps farther from the edge of the trench until the saturation levels stabilize
• Keep powered mobile equipment away from the edge of the excavation
• Watch the trench, paying attention to its walls.
• If there is soil saturation, the trench may require shoring.
• The evacuation plan must cover egress from the excavation.

If you use water removal equipment, a competent person must monitor the operation and ensure correct use. If the excavation interrupts surface water drainage, OSHA standards require diversion ditches, dikes or any other appropriate means to prevent water from entering the excavation.

Contact NASP for Trenching and Excavation Safety Training

At the National Association of Safety Professionals, we understand the importance of recognizing excavation and trenching hazards. Our mission is to provide safety professionals with innovative and thorough training on OSHA standards and more. We separate ourselves with our unique training that emphasizes dynamic learning for adults.

Learn more about our trenching and excavation safety training opportunities. Our safety course prepares you for trenchwork hazards and how to navigate them safely. The lessons address potential risks at trench sites and how to best manage them for the safety of your team. Contact us today with any questions about our safety training courses. Have a group of 8 or more that require this training? NASP is available for instructor-led trenching and excavation ‘competent person’ training as well. Call us at 800-922-2219 for details.