Digging Deeper: Top Trench Safety Hazards and Ways to Mitigate

Digging Deeper: Top Trench Safety Hazards and Ways to Mitigate

Trench work and excavations are among the most dangerous construction operations and can involve serious hazards to workers. According to a Trenching and Excavation Safety publication by OSHA, “One cubic yard of soil can weigh as much as a car. An unprotected trench can be an early grave.”

However, many of the injuries that occur in trenching are preventable. With planning, precautions, and protective systems in place, trench work can be done safely and efficiently. Read on to learn more about trench hazards and mitigation.

Trench vs Excavation

Before digging into trench safety, it’s important to understand what exactly a trench is. Per OSHA, trenches comprise a subset of excavations made below the ground’s surface that are narrow (in relation to their length) and deep (in relation to their width). They are commonly used for utility installation or repair, foundation preparation, drainage, piping, and cable installation.

Excavations can be used for similar purposes but are generally broader and encompass a wider variety of digging projects. Though they are not always one and the same, trenches and excavations are both inherently dangerous and must be approached with caution and planning.

Trench Hazards and Mitigation

While not the only hazard associated with trenches, cave-ins tend to be the most fatal. Cave-ins occur when a trench wall suddenly collapses, causing soil to fall into the trench and potentially bury or trap workers within seconds. Below, we’ll explore cave-ins and other common trench hazards and how safety professionals can work to prevent them.

Hazard: Cave-ins. Per OSHA, “Cave-ins pose the greatest risk and are more likely than some other excavation-related incidents to result in worker fatalities.” OSHA reports that 40 workers die each year in the United States from cave-ins, on average.

Mitigation: Prevention of cave-ins is critical. Protective systems like sloping, shoring, or shielding must be used, and daily inspections of trenches by a competent person should take place, especially after rain or the use of vibrating equipment that may have disturbed the soil. It’s also important to keep spoil piles at least two (2) feet from the edge of the trench to reduce added pressure on trench walls.

Hazard: Falls. Though cave-ins may be the biggest hazard to those working in trenches, falls are also common; workers and bystanders are at risk of falling into the trench. This can be more likely to occur when workers cross over trenches to get to the other side, or if the area isn’t clearly marked or protected.

              Mitigation: According to OSHA, fall hazards can be mitigated by “putting up safety signs, installing guardrails for walkways that are six (6) feet or higher from the bottom of the trench or the lower level, and/or placing barriers around the edges of trenches and excavation sites.” OSHA also requires ladders to be provided in trenches four (4) feet or deeper.

Hazard: Utility strikes. Accidentally digging into electrical, gas, or water lines can cause explosions, electrocution, flooding, or other severe injuries.

              Mitigation: If you’re in the U.S., always call 811 before digging to locate underground utilities, and use safe digging practices around lines. Check out our Call Before You Dig guide for more information on safe digging.

Hazard: Hazardous atmospheres. A less obvious risk associated with trenches is hazardous atmospheres, like those with low oxygen levels, toxic gases, or flammable vapors.

              Mitigation: Always conduct air monitoring before entering a trench, especially those deeper than four (4) feet. If you detect concerning conditions, use appropriate PPE or delay entry until the hazard is resolved by a qualified professional.

Hazard: Mobile equipment operating. Excavators, dump trucks, and other equipment can cause serious injuries if they strike workers or destabilize trench walls. When equipment is closer to trench edges, accidental collapses or falls are more likely.

              Mitigation: Keep equipment a safe distance from the edge of the trench, and use barricades or stop logs to prevent overrun. Maintain clear communication between operators and ground crews, and use spotters or flaggers when needed.

The Importance of Preplanning

In addition to following OSHA’s excavation standards, 29 Code of Federal Regulations (CFR) Part 1926, Subpart P, safety professionals should also prepare for trench work by planning. Before trenching begins, a competent person should, for example, determine the soil type, plan for safe trench entry and exit, and know the estimated location of underground utilities.  

As Trenching and Excavation Safety puts it: “No matter how many trenching, shoring, and backfilling jobs an employer has done in the past, it is important to approach each new job with care and preparation. Many on-the-job incidents result from inadequate initial planning. Waiting until after the work starts to correct mistakes … slows down the operation, adds to the cost of the project, and makes a cave-in or other excavation failure more likely.”

 

 

References:

OSHA. (2015). Trenching and Excavation Safety. Retrieved from https://www.osha.gov/sites/default/files/publications/osha2226.pdf.

 

Tags: Trench Safety Trenching Trench Hazards Trenching and Excavation Safet OSHA

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