HR Management & Compliance

Are Your Workers Trained on this By-the-Numbers Approach to Excavation Safety?

It’s mid-June and construction season is well underway across the USA. That means this is a necessary time for training on excavation and trenching safety. In today’s Advisor, we get valuable training information from BLR® Legal Editor Ana Ellington.

All excavations are hazardous because they are inherently unstable. If they are restricted spaces, they present even more dangers, such as oxygen depletion, toxic fumes, and accumulation of water. You must ensure that you are using protective systems or equipment while working in trenches or excavations at your worksite to prevent the dangers of suffocation, fire, drowning, or being crushed by a cave-in. An unprotected trench is an early grave.
Preplanning the job is vital to accident-free trenching! It is one of the most important steps to avoiding cave-ins in excavations. Safety cannot be on the spur of the moment as the work progresses. Ensure your workers know the basic how-to’s of preplanning.
In addition, the Occupational Safety and Health Administration (OSHA) requires that you designate a competent person to inspect trenches daily before each shift and as conditions change before workers can enter the trench. Excavation site inspections must be conducted by a competent person who:

  • Has training in soil analysis.
  • Has training in the use of protective systems.
  • Is knowledgeable about the OSHA requirements.
  • Has authority to immediately eliminate hazards.

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Here are some questions that must be answered before digging.

  • Are there any underground utilities? Contact utilities (gas, water, electric).
  • What types of soil will be found?
  • What are the soil moisture conditions?
  • Has the soil previously been disturbed?
  • How large will the excavation be?
  • How long will the excavation be open?
  • What kinds of weather can be expected?
  • What kinds of equipment will be on the job?
  • Will the excavation be near structures?
  • Is traffic control needed near the excavation?
  • What sources of vibration will be nearby?
  • Will water be a problem?
  • What kind of shoring is necessary? How much?

Trenching and Excavation ‘By the Numbers’
Catherine Zinsser, Occupational Safety Training Specialist at CONN-OSHA, provided this list for training workers and planning excavations at a recent trenching and excavation training course. Though not all-inclusive, the list is very useful.
1 qualified person—Must perform an ongoing inspection of an excavation or trench.
2 days—Contact utilities 2 days before excavation.
2 feet—Spoils, surcharge, or other material or equipment must be set back 2 feet from the excavation.
2 feet—Excavating no more than 2 feet below members of support or shield is permitted, if the system is designed for the full depth of the trench and there is no loss of soil from behind or below the system.
3 feet—Ladders must extend not less than 3 feet above the top of the trench.
4 feet—Stairways, ladders, or ramps are needed in excavations 4 feet or more in depth.
4 feet—In excavations greater than 4 feet, the atmosphere must be tested if oxygen deficiency or hazardous atmosphere does, or is reasonably expected to, exist.
5 feet—Excavations less than 5 feet in depth do not require a protective system if the competent person examines and determines there is no potential for a cave-in.
6 feet—Guardrails are required on walkways that are over excavations 6 feet or more above lower levels.
18 inches—In sloped systems with vertically sided lower portions, the trench boxes must extend 18 inches above the top of the vertical sides.
19.5 percent—A minimum of 19.5 percent oxygen must be present before employees can enter an excavation greater than 4 feet in depth.
20 feet—Sloping, benching, or timber and aluminum hydraulic shoring for excavations greater than 20 feet must be designed by a registered professional engineer.
20 percent—Adequate precautions must be taken, such as ventilation, to prevent employee exposure to an atmosphere containing a concentration of a flammable gas in excess of 20 percent of the lower flammable limit of the gas.
24 hours—Simple slope excavations in Type A soil that are open for 24 hours or less (short-term) and that are 12 feet or less in depth must have a maximum allowable slope ½ horizontal to 1 vertical.


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25 feet—For excavations 4 feet or more in depth, ladders, stairways, or ramps are needed so lateral travel for employees is no more than 25 feet.
34 degrees—The maximum allowable slopes (degrees from the horizontal) for excavations less than 20 feet in Type C soil (29 CFR 1926 Subpart P Table B-1).
45 degrees—The maximum allowable slopes (degrees from the horizontal) for excavations less than 20 feet in Type B soil (29 CFR 1926 Subpart P Table B-1).
53 degrees—The maximum allowable slopes (degrees from the horizontal) for excavations less than 20 feet in Type A soil (29 CFR 1926 Subpart P Table B-1).
90 degrees—The maximum allowable slopes (degrees from the horizontal) for excavations less than 20 feet in stable rock (29 CFR 1926 Subpart P Table B-1).
In tomorrow’s Advisor, we’ll offer 12 trenching tips that could save lives.