While trenches and excavations are essential for many construction processes, they also present potential hazards for workers. In the 2010s, about 20 workers died from trench-related accidents each year. Trenches are challenging to access, and they face the risk of collapse. They might also contain hazardous atmospheric conditions. Understand more common trenching and excavating dangers to prepare for them properly.

Trenching and Excavation 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, professionals must thoroughly inspect the area for potential dangers. After employers enact the correct protective measures, workers can start working underground.

Even after thorough inspections of the surrounding area, excavations can present many risks to employees. The soil overhead can weigh almost as much as a car. Potential collapses or falls might lead to suffocation or death. It’s important to be aware of trenching and excavation hazards so employees can avoid accidents.

Here are common hazards of trench and excavation jobs.

1. Collapses or Cave-ins

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

These are common 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 one of the biggest threats to trench stability. Flooding or heavy rainfall might cause water accumulation at the bottom of the trench and weaken the walls’ strength. According to Occupational Safety and Health Administration (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.

Collapses threaten the lives of workers and undermine entire excavation projects. It’s essential to 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 Air

Another example of trenching and excavation dangers is hazardous air. Oxygen deficiencies and toxic air conditions are common below ground. Exposure to dangerous toxins might cause respiratory issues or diseases, so they present a serious danger to workers.

During daily inspections, supervisors should ensure air conditions are suitable for workers before they 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 located near landfills or chemical plants. Contaminated air could travel from the site and accrue in the trench. This may include hydrogen sulfide gas from sewer lines or carbon monoxide from running equipment. In these cases, it’s important to have emergency procedures in case the air becomes too toxic.

According to OSHA, supervisors should test atmospheres in trenches and excavations deeper than 4 feet. If oxygen levels are less than 19.5%, OSHA considers that Immediately Dangerous To Life or Health (IDLH).

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. If workers hit one of these lines or uncover a line that isn’t insulated properly, the outcome could be dangerous. Damaging municipal lines is both 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 also 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 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. If materials or equipment sit too close to the edge of the trench, they could fall into the excavation.

These are some dangers that could occur because of 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 might also damage or block exits of the trench, trapping workers below.
  • Head trauma or injury: If falling materials strike someone’s head, this 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.

Contact NASP for Trenching and Excavation Safety Training

At the National Association of Safety Professionals, we understand the importance of recognizing trench 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.

Purchase Our Excavation Safety Training Course

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.
Home » Blog » Common Trenching and Excavation Hazards