19 Dec 2014
Using cave-in protective equipment when working in trenches deeper than five feet isn’t just a good idea. It’s the law.
That’s what the owners of A. Lamp Concrete Contractors — a construction company in Morton Grove, Illinois — found out the hard way last week when they were fined $69,300 by the US Occupational Safety and Health Administration for failing to adequately protect its workers from cave-ins during trenching operations.
The violation stems from an incident that occurred June 4 when an OSHA inspector discovered two of the company’s employees installing a water main in Morton Grove inside an 8-foot trench without cave-in protection, according to an OSHA news release.
OSHA trenching standards require all excavation deeper than 5 feet to be protected against collapse.
Heavy and Fast-Moving
Soil is extremely heavy and can be fast moving if not supported. As single cubic foot of soil weighs about 114 pounds and a cubic yard weighs about 1.5 tons, or about the same as a Volkswagen Beetle.
A worker buried under only a few feet of soil can be crushed by so much pressure that the lungs can’t expand and suffocation can occur in as little a three minutes. Soil that is wetter and heavier can crush the body in just a few seconds.
Protective systems reduce the likelihood of soil cave-ins that can fall or roll into an excavation. They also are used to support nearby structures to prevent collapse caused by the excavation.
Types of Protection
Anytime a ditch or trench is dug between 5 and 20 feet deep, construction managers and project planners must use protective measures such as shoring and sheeting, shielding, or sloping and benching, according to OSHA regulations. If an excavation is deeper than 20 feet, a registered professional engineer is required to design a protective system.
Shoring systems are designed to prevent cave-ins and usually are structures of timber, mechanical or hydraulics that support the sides of an excavation.
Sheeting is a type of shoring that keeps the soil in position and is either driven into the ground or works with a shoring system. Driving sheeting is typically used for excavations that will remain open for long periods of time.
A shield, or trench box, is commonly used in pipe laying. It is a concrete or metal box that “shields” workers within a structure should a cave-in occur. The box is placed in the trench and then dragged along with the progress of the work.
With both shoring and shielding, workers are only protected if they stay within the confines of the system.
Sloping and benching is a method of cutting back a trench wall at an angle so that there is little chance of collapse. This is known as an “angle of repose” and the angle of the slope depends on the type of soil being controlled. For the most common types of excavations, the walls must be sloped back on each side of the excavation 1 and 1.5 feet for every 1 foot of depth.
Sloping and benching is the least used type of cave-in protection because it requires more space, which is often impractical when working in busy area.