Excavation safety, while being a concern of the contractor, is also of great concern to OSHA. In fact, Subpart P- Excavations of the OSHA construction regulations (Part 1926) is one of the largest sections in the Code of Federal Regulations (the OSHA regulations “codebook”). A careful review of this entire subpart is necessary before any excavation work is performed.

Cave-ins are a leading cause of injuries and fatalities to workers in excavations. Therefore this article will primarily focus on OSHA’s regulations for the protection of workers from this potential hazard.

OSHA outlines the importance of having any affected underground utilities or installations located before any excavation work can start. While this is an OSHA regulation, locating underground utilities is frequently covered by local regulations and practices. OSHA will allow excavation work to start and continue without locating being performed by the utilities – if the utilities did not respond in a timely fashion. In this event, the contractor should proceed cautiously, and with his own locating equipment, probes, or other means to prevent damage to any utilities in question. Any underground utilities uncovered are required to be protected, supported, removed, or otherwise safeguarded from workers.

When excavations are performed in stable rock, personnel protection (from cave-ins) is exempted by OSHA. However, when excavations in all other materials (soil, sand, etc.) exceed five feet (5 ft.) in depth, you are required by OSHA to have at least one of three methods of personnel protection. These three methods are: sloping (or stepping) the excavation walls, shielding the excavation walls (trench boxes), and shoring the excavation walls.

The method(s) you choose may depend on size, type and location of the excavation; soil types; equipment availability; and of course, the economics of a particular project.

Sloping or stepping excavation walls:

The degree of slope depends on the stability of the soil or material being excavated. OSHA has devised a soil rating where Type “A” soil has the highest stability, Type “B” soil (including unstable rock and granular fills) has the next highest stability, and Type “C” soil (including sand, gravel, and submerged soils) has the lowest stability. A competent person, designated by the employer, or a soils engineer must determine which type of soil or material that is being excavated before determining the correct angle of slope for an excavation. The correct angle of slope is fifty three degrees (530) for type “A”, forty five degrees (450) for type “B”, and thirty four degrees (340) for type “C”. Stable rock may be excavated with a vertical (900) wall. According to OSHA, the values given here may be increased or reduced if a registered professional engineer is used to design an alternative excavation plan. In this case, OSHA would typically accept the engineer’s decision for what slopes, if any, to use.

Shields, or trench boxes:

Shields or trench boxes are designed to protect the worker(s), not the excavation from collapse. This is because the trench box is freestanding, and it’s sides typically do not bear against the excavation’s walls. Rather these shields are placed on the floor of an excavation where work is being performed, and moved or relocated as work progresses. In the event of a collapse, workers inside the shield or trench box would be protected. Workers need to access the shielded area within the excavation (by ladder or other safe means) in lieu of walking into the unprotected area to enter or exit the excavation.

This is part one of a two part series on Excavation Safety.