Designing and Planning an Excavation
Constructing an Excavation
Working Safely in and around Excavations
29 CFR 1926 Subpart P – Excavations
1926.650 - Scope, Application & Definitions
1926.651 - Specific Excavation Requirements
1926.652 - Requirements for Protective Systems
1926 Subpart P, Appendix A - Soil Classification
1926 Subpart P, Appendix B - Sloping and Benching
1926 Subpart P, Appendix C - Timber Shoring for Trenches
1926 Subpart P, Appendix D - Aluminum Hydraulic Shoring for Trenches
1926 Subpart P, Appendix E - Alternatives to Timber Shoring
1926 Subpart P, Appendix F - Selection of Protective Systems
29 CFR 1926.50 – Medical Services and First Aid
29 CFR 1926.502 – Fall Protection Systems Criteria and Practices
Evaluate whether excavations have been designed to ensure adequate support, stability, and safe employee access/egress.
Prepare, conduct, and complete excavations without compromising adjacent structures or utility lines.
Work safely in and near excavations – minimizing common hazards, while using appropriate testing, protective, and rescue techniques and equipment.
Trenching and excavation hazards result on an average of 54 fatalities each year. 68% percent of those fatalities occur in companies with fewer than 50 workers. 46% of the deaths occur in small companies with 10 or fewer workers.
LABOR RESEARCH, NIOSH
For the utility industry, excavation work is about digging large trenches for cables, digging smaller holes for power lines or vaults. The Occupational Safety & Health Administration’s (OSHA) excavation standard requires a "competent person" to make several key determinations.
How To Determine Who Qualifies as a "Competent Person"
They must be capable of identifying existing, regular hazards in excavation work.
They must have been trained in and be knowledgeable about: soils analysis, the use of protective systems, and other requirements of OSHA’s 1926 (P) standard.
They must have the authority to take prompt measures to reduce any hazards.
Before any digging starts, a qualified person needs to create an excavation design that meets specific safety standards, established to prevent potentially deadly cave-ins. These standards include getting safely in and out; sloping and benching systems, and supports, shields, and other protective systems. Someone on a work team has to think through the situation.
Getting In and Out Safely
In any excavation more than four feet deep, a qualified person must check that there are stairs, ladders, ramps, or other safe methods of entry and exit. Structural ramps are used to get equipment in and out. The qualified person must make sure that entry and exit devices are frequent enough that no worker needs to travel more than 25 feet, laterally, to reach one. Ladders must extend at least three feet above the excavation’s openings.
When using of structural ramps instead of steps, the ramps must provide cleats, or other surface treatment, to prevent slipping. Ramps’ structural members must be connected on the bottom of the runway to minimize tripping risks on the surface.
Structural ramps—found mostly in larger excavations—must be designed by a competent person, who is qualified in structural design, and must be built to match the design. When using ramps or runways constructed of two or more structural members, the structural members must be connected together to prevent movement, and must be of uniform thickness.
Designing a Safe Excavation
Sloping and benching are two approaches to designing a safe excavation. One option is to slope the excavation at an angle no steeper than 1 & ½ horizontal, to 1 vertical. (That’s 34 degrees, measured from the horizontal.) But because utility rights-of-way are typically too narrow for trenches that wide, you rarely see sloping systems in electrical excavations.
Another option is to follow the OSHA standard’s Appendices A and B. These lay out maximum allowable slopes and allowable configurations for sloping and benching systems.
A third option is to design the sloping or benching system according to tabulated data, such as manufacturers’ tables and charts.
Supports, shields, and other protective systems provide primary defenses against cave-in’s. Some common examples include: temporary shoring with jacks and plywood, trench boxes, and aluminum hydraulic shoring. For protective systems to really protect a work team, the safety pro must ensure that these systems’ materials and equipment stay in excellent condition. Always check for flaws, use as directed, inspect damage, manage upkeep, and get an engineer’s approval if needed.
Before opening an excavation, workers must locate and protect any existing utility installations on the site.
Visual and Physical Soil Testing
A competent person must evaluate what class of soil workers are dealing with, based on at least one visual and one physical test. Do the visual test as soon as excavation starts, then, as the spoil pile grows, perform a thumb-and-finger roll , or ribbon, or penetrometer test on a dirt clod, to determine the soil’s compressive strength, elasticity, and cohesiveness. The less stable the soil, the more robust the support system you might need to construct, to handle expected loads.
Excavations create hazards if done improperly or with defective equipment. Safe trenching practices are highly encouraged. In subterranean high-risk work environments, there is a lot that can go wrong. It is worth it to follow the rules, proceed with caution, and keep a high level of awareness.
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