Shoring

Shoring, unlike shielding, is a system that applies pressure against the excavation’s walls to prevent collapse, rather than protection from collapse. Shoring applies pressure to members placed against the excavation’s walls by use of hydraulic, pneumatic, or mechanical means creating a constant outward force. As with shields or trench boxes, shoring is set in place after excavation and before any work is performed. Shoring is then removed after work in the excavation has occurred. Access to the shored excavation needs to be within the protection of the shoring as well.

Once work starts on an excavation, a competent person needs to inspect any work performed at least daily before the work starts and throughout the day as needed. Also, when the condition of an excavation is subject to changes (such as a rainstorm), an excavation is required to be reinspected before work resumes or continues. OSHA frequently cites contractors for failure to perform these inspections, and to have a competent person onsite. Other common OSHA citations to be aware of are; not having egress points (ladders, ramps, or other means) a maximum of fifty (50 ft.) apart to allow quick exits for workers; not keeping spoils, tools, equipment, and materials at least two feet (2 ft.) from the excavation’s edge; and not having any excavation work twenty feet (20ft.) or greater in depth designed by a registered professional engineer.

While OSHA requires personnel protection in excavations more than five feet (5 ft.) in depth, OSHA regulations may also require (in certain circumstances) the same protection methods for excavations of lesser depths. OSHA regulation 1926.652(a)(I)(ii) exempts use of personnel protection in excavations less than five feet (5 ft.) in depth when “…examination of the ground by a competent person provides no indication of cave-in.”

For example, if work is being performed in a four foot (4 ft.) deep trench with vertical walls and with non-cohesive soils or where cracking, weakening, or crumbling soil conditions exist (as with type B or C soils), then a potential hazard exists for workers within the trench, especially those who may be bent over or on their knees working. This situation, therefore, would require use of personnel protection at an excavation depth of less than five feet.

Although this may seem an obscure, or rare occurrence, I found in conversation with OSHA Compliance Safety and Health Officers (CSHO’s), that citations have been issued for no personnel protection in excavations less than five feet. CSHO’s however, would likely address each situation on a case-by case basis. Therefore, all excavations regardless of depth need to be assessed by the competent person before a decision is made whether or not to provide personnel protection.

Attention to forming a work plan before excavating will benefit workers and contractors alike by creating a safe work environment free from potential hazards and liability for the worker, and the contractor alike.

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.