Trenching and Excavation Safety a Top Priority on Construction Sites

trenching in constructionTrenching and excavation are widely recognized as among the most hazardous construction operations, resulting in an average of two deaths per month and hundreds of injuries each year due to trench collapses. OSHA has addressed construction-related trenching and excavation hazards by developing specific safety standards for the construction industry, making the requirements easier to understand and providing construction employers with various options for classifying soil and selecting employee protection methods.

OSHA defines an excavation as any man-made cut, cavity, trench or depression in the earth’s surface formed by earth removal. A trench is defined as a narrow excavation made below the surface of the ground with a depth greater than its width and a maximum width of 15 feet at the bottom.

The primary hazard of trenching and excavation is the potential for collapse. Since one cubic yard of soil can weigh as much as a car, cave-ins pose the greatest risk and are much more likely than other excavation-related accidents to result in worker fatalities or serious injury. An unprotected trench can literally become an early grave. Additional excavation hazards include the use of heavy machinery for digging; electrical hazards from overhead and underground power-lines; underground utilities, such as natural gas; falling loads; and hazardous atmospheres.

Excavation Protective Systems

Trenches 5 feet deep or greater require a protective system unless the excavation is made entirely in stable rock. Trenches 20 feet deep or greater require that the protective system be designed by or based on data prepared and/or approved by a registered professional engineer.

A variety of protective systems can be utilized to reduce or eliminate trenching and excavation hazards, including:

  • Benching – cutting the sides of an excavation to form one or a series of horizontal levels, or steps, usually with vertical or near vertical surfaces between levels;
  • Sloping – cutting back the trench wall at an angle inclined away from the excavation;
  • Shoring – installing aluminum hydraulic or other types of supports to prevent soil movement;
  • Shielding – using trench boxes or similar types of supports to prevent soil cave-ins.

Among the many factors to be considered in the design of protective systems are: soil classification, depth of cut, water content of soil, changes due to weather or climate, surcharge loads (e.g., other materials to be used in the trench) and other operations in the vicinity.

OSHA requires safe access and egress for employees working in trench excavations 4 feet or deeper, such as ladders, steps, ramps or other safe means of to be located within 25 feet of all workers.

General Trenching and Excavation Rules

When working in or near a trenching and excavation site, the following steps should be taken:

  • Keep heavy equipment away from trench edges
  • Keep surcharge loads, including excavated soil (spoils) and other materials, at least 2 feet from trench edges
  • Know where underground utilities are located before digging
  • Test for atmospheric hazards such as low oxygen, hazardous fumes and toxic gases in trenches deeper than 4 feet
  • Inspect trenches at the start of each shift
  • Inspect trenches following a rainstorm
  • Inspect trenches after any occurrence that could have changed conditions in the trench
  • Do not work under suspended or raised loads and materials

For additional information on trenching and excavation safety, see OSHA Trenching and Excavation Fact Sheet and OSHA Working Safety in Trenches Quick Card.

About the OSHA Training Center

The OSHA Training Center at Chabot-Las Positas Community College District offers high quality Occupational Safety & Health Administration standards-based training for construction, maritime and general industry at its Center in Dublin, California, as well as locations throughout California, Arizona, Nevada, Hawaii and Guam. Programs offered include OSHA safety standards, Outreach Trainer courses, Cal/OSHA standards curriculum, environmental courses and customized on-site safety training. Upcoming courses include Excavation, Trenching and Soil Mechanics and Managing Excavation Hazards. For more information, including a complete course schedule, visit the OSHA Training Center website or call (866) 936-OSHA (6742).


  1. Nicely done. Only wish that you had noted that a protective system is required if there is potential for a cave-in when the excavation/trench is less than five feet deep. See Appendix F.

    Workman comp claims, injuries, and occasionally fatalities continue in significant numbers due to the continuing myth, mostly on the part of plumbers, mechanical, electrical, communication, and water and street municipal departments that until you are five feet or more…you do not have to do anything.

    When possible…that myth must be addressed.


  2. Delores Lyon says

    I think it is really great that you take safety seriously. It is important that any type of contractor is extremely safe. You definitely don’t want to end up causing major damage to the property around you. In fact, i wouldn’t hire a contractor unless I knew that they took safety really seriously.

  3. Knowing that there are “two deaths per month and hundreds of injuries each year due to trench collapses” is a frightening thing. I admire those who are brave enough to do this kind of work. After I read the safety requirements I found a little bit more comfort. If I worked in this area, I would be sure to never break a safety rule. Especially if it put lives at risk.

  4. I had no idea that Trenching is as dangerous as it is and didn’t even know there was that much of a hazard. I’ve seen some pretty big pipe systems put under the roads by where I live throughout the years and never thought much of it. I also thought the different ways they excavate was interesting, mostly because I was a kid that grew up playing in the sandbox and it was the worst when cave-ins happened!

  5. I didn’t know that trenches that are 5 feet deep needed a protective system! I appreciate the ideas to prevent this hazard, such as benching. I think that if I don’t use “benching” near my trench, I’ll probably use the “shielding” method. Thanks for this help!

  6. I am glad that people go to such measures to insure construction worker’s safety. Excavation can a dangerous, so the benching, sloping, shoring, and shielding methods should be utilized. Thanks for sharing the information, hopefully everyone is following these safety rules!

  7. Hello Julia!
    Your article is informative, I like how you discussed this topic. Safety should really be the top priority on ever construction site to avoid any accidents. I also like that you added the step of rules for trenching and excavation, it’s like a basic knowledge that every excavation worker/company should always keep in mind but it’s also nice to read something like this and be reminded from time to time.
    Cheers to you!

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