Trenching and Excavations: Considerations for the Competent Person
There is no blanket requirement that a competent person must be present at a construction job site at all times. The competent person can periodically leave the site. It is the responsibility of the competent person to make inspections necessary to identify situations that could result in hazardous conditions (e.g., possible cave-ins, indications of failure of protective systems or hazardous atmospheres), and to then ensure that corrective measures are taken. The hazards and conditions at each work site determine whether or not a competent person is required to be present at the job site at all times. When trenching and excavation work takes place, the competent person has several important responsibilities. This Tailgate will guide you through some of the critical tasks and issues the competent person faces while striving to maintain a safe trenching environment for workers.
Competent Person Responsibilities
By definition, a competent person has the authority to make changes and stop work when safety is being compromised. In this role, you must conduct daily inspections of excavations, the adjacent areas and protective systems. Look for signs of soil distress such as fissures or cracks on the excavation face, slumping of material from the excavation face, bulging or heaving of material at the bottom of the excavation wall, sinking of the excavation’s edge, raveling and small amounts of material trickling into the excavation. As the competent person, you also must consider nearby vibrating machinery or heavy, moving loads, as well as hot, dry weather.
Another area for consideration is hazardous atmospheres. Check excavations to determine if they are near sewers, landfills or hazardous substances storage areas. If so, test the atmosphere when deeper than 4 feet. The competent person must evaluate the rescue and emergency equipment available, and also will need to evaluate if the excavation might endanger the stability of buildings, walls or other structures. Sidewalks and pavement must be assessed to confirm they have not been undermined and will not collapse on excavation workers. Make certain that proper shoring, bracing or underpinnings are used to ensure stability and employee protection.
The competent person should never allow workers in an excavation where water is accumulating without taking proper precautions such as shoring or having a shield system in place, and using a water removal system. A competent person must always be present when shoring is being used, when it is being moved frequently and when de-watering is constant. If there is risk of a cave-in, workers are required to be removed from the trench.
Other issues that you need to consider as a competent person are the marking of underground utilities and the use of warning systems and barricades. Excavations shall be no greater than 2 feet below the bottom of a shield, which is often designed to stack and can be used in conjunction with sloping and benching. No one shall be permitted inside shields when the shields are being raised, lowered or moved.
Soil Types and Hazards
The competent person must be familiar with the ins and outs of each type of soil and the hazards they present. Many companies have adopted a routine of classifying all disturbed soil as Type C. Benching of Type C soil is unacceptable and not permitted. However, classification of soil requires compressive or manual tests. It is not uncommon to test old trenches and determine they consist of Type B soil, therefore allowing benching.
Be aware that suffocation can occur even if the worker’s head is not buried because pressure from the soil restricts blood flow and respiration. Also remember that all shoring must be designed by a professional engineer and accompanied by tabulated data. A shoring system can be installed by a qualified person who, by experience or degree, recognizes the hazards of an excavation and is under the supervision of a competent person.
By the Numbers
Finally, there are several number-related rules and regulations the competent person must know and enforce when performing trenching and excavation work. Following is a list for easy reference:
• One competent person is required to perform daily inspections, classify the soil and risks, and develop and supervise a protection system.
• A spoil pile should be at least 2 feet from the trench or excavation.
• Ladders must extend 3 feet above a trench.
• Trench excavations 4 feet deep or greater require a ladder or other safe method of ingress/egress.
• Trenches 5 feet deep or greater require trench wall stabilization through sloping, shoring or shielding.
• Trenches 6 feet deep or greater require fall protection.
• A safe means of egress must be located within 25 feet of all workers.
• There must be 18 inches of shield above ground level.
About the Author: Lt. Col. Charles R. Southerland, CSC, CUSP, is director of management services for Morristown Utility Systems. He has worked in the utility industry for more than 35 years in a variety of capacities and has earned numerous safety certificates from the EPA, OSHA and FEMA. Southerland also acts as a consultant for the Tennessee Valley Public Power Association and previously served as an instructor for the Tennessee Emergency Management Agency.