Excavating is one of the most hazardous construction operations and the Occupational Safety and Health Administration (OSHA) has stringent guidelines aimed at protecting employees involved in the work. In particular, cave-ins rank at the top of the list of hazards facing employees.
OSHA is aware that a number of factors make it difficult to design protection against cave-ins, including soil classification, depth of cut, the water content of soil, changes due to climate and other operations in the vicinity. Consequently, the agency allows several different prevention methods including:
1. Supporting the sides of the excavation.
2. Sloping, or benching. This method involves sloping the sides of an excavation to an angle not steeper than one and one-half horizontal to one vertical (34 degrees measured from the horizontal). These slopes must be excavated to form configurations that are in accordance with those for Type C soil found in Appendix B of the standard. A slope of this gradation or less is considered safe for any type of soil.
All simple slope excavations 20 feet or less in depth in Type C soil have a maximum allowable slope of 1 1/2:1.
Another method, which can be applied for both sloping and shoring, involves using tabulated data, such as tables and charts, approved by a registered professional engineer. These data must be in writing and must include sufficient explanatory information to enable users to make a selection.
At least one copy of the information documents, including the name of the registered professional engineer who approved the data, must be kept at the worksite during construction of the protective system. Upon completion of the system, the data may be stored away from the job site, but a copy must be made available, upon request, to OSHA officials.
3. Placing a shield between the side of the excavation and the work area. Contractors also may use a trench box or shield that is either designed or approved by a registered professional engineer or is based on tabulated data. Timber, aluminum, or other suitable materials may also be used.
OSHA standards permit the use of a trench shield (also known as a welder's hut), as long as it provides protection equal to or greater than what would be provided by the appropriate shoring system.
Preliminary Work Regulations
Before excavation actually begins, OSHA requires employers to:
- Estimate the location of utility installations — sewer, telephone, fuel, electric, water lines, or any other underground installations — that may be encountered during digging.
- Contact the utility companies or owners involved and inform them of the proposed work.
- Ask utility companies or owners to find the exact location of the underground installations. If they can't respond within the time specified by local or state law, or if they can't find the exact location of the utility installations, the contractor can proceed with caution.
- Use safe and acceptable means to find the locations of underground installations. If installations are exposed, OSHA regulations require that they be removed, protected or properly supported.
Warning: OSHA cautions that: "No matter how many trenching, shoring and backfilling jobs have been done in the past, each job should be approached with the utmost care and preparation."
A Willful Employer
In one case that illustrates the penalties that can be imposed, OSHA fined a Houston construction company nearly $100,000 for violating standards to protect employees from cave-ins.
Regulators determined that the shoring system wasn't designed to protect employees working at a depth greater than 25 feet.
The agency alleged that the company failed to:
- Adequately train employees on the hazards of entering a confined space.
- Provide training on the use of protective equipment.
- Install informational signs at hazard points.
- Provide guardrails, fences or covers to prevent falling into excavation depths of more than six feet.
- Place excavated materials at least two feet from the trench's edge.
OSHA's charges included both willful and serious violations of safety standards. A "willful violation" is intentional disregard of, or indifference to, regulations set by the Occupational Safety and Health Act. A "serious violation" indicates the company knew, or should have known, that the hazard had a high probability of resulting in death or serious injury.
