Access, egress, spoil and edges

A trench with a perfect protective system can still kill people who cannot get out of it quickly, who are struck by a load swung over it, who fall into it, or who are buried when a spoil pile or a parked truck pushes the edge in. This lesson covers the ground around and above the excavation: ladders and ramps, spoil and surcharge, mobile equipment, falling loads, barriers and covers, and protecting the public and nearby structures.

Getting in and out

Workers need a safe way in and a safe way out, close enough that they can escape quickly if water rushes in, a wall starts to move, gas is detected or someone is injured. Climbing the walls, riding the bucket, using shoring members as a ladder or jumping in from the edge are all prohibited.

OSHA 1926.651(c)(2) requires a stairway, ladder, ramp or other safe means of egress in trench excavations 4 ft or more deep, located so that no worker has more than 25 ft of lateral travel to reach it. Ladders must meet Subpart X: portable ladders used for access to an upper landing must extend at least 3 ft above the landing or be secured at the top with a grab rail, and must be secured against displacement. Structural ramps used only by workers must be designed by a competent person; ramps used by equipment must be designed by a competent person qualified in structural design.

Spoil and surcharge

Excavated soil, called spoil, is heavy and close at hand, which is exactly why it ends up in the wrong place. A spoil pile at the edge adds weight to the wall, can slide or roll back into the trench, and hides cracks that would warn of movement. Materials such as pipe, precast structures, bedding stone and timber, and equipment such as compactors and pumps, create the same problems.

OSHA 1926.651(j)(2) requires employees to be protected from excavated or other materials or equipment that could fall or roll into the excavation, by placing and keeping such materials or equipment at least 2 ft from the edge, by using retaining devices sufficient to prevent them from falling or rolling in, or both. Materials that add load near the edge must also be considered when choosing a protective system, and 1926.651(i) requires support systems or other protection where adjacent structures could be undermined.

These distances are minimums. Heavy surcharges such as large spoil piles, loaded trucks, cranes and stacked precast should be kept further back, and their effect on the protective system considered. A practical guide used by many engineers is that loads within a distance from the edge roughly equal to the depth of the excavation affect the walls, and that a protective system designed without a surcharge allowance may not be adequate when heavy equipment works alongside.

Mobile equipment near the edge

Excavators, loaders, dump trucks, concrete trucks and cranes are heavy, vibrate the ground and can tip into the excavation if the edge gives way. Operators often cannot see the edge from the cab.

OSHA 1926.651(f) requires a warning system, such as barricades, hand or mechanical signals, or stop logs, when mobile equipment is operated next to an excavation or must approach its edge and the operator does not have a clear and direct view of the edge. 1926.651(d) requires workers exposed to vehicular traffic to wear high-visibility warning vests.

Excavators should normally dig from the side opposite the spoil pile, track at right angles to the trench rather than along the edge, and set their outriggers or tracks well back from any unsupported wall. Trucks being loaded should stay outside the surcharge zone or the protective system should be designed for them.

Falling loads and swinging buckets

OSHA 1926.651(e) prohibits employees from being underneath loads handled by lifting or digging equipment, and requires them to stand away from vehicles being loaded or unloaded to avoid being struck by spillage or falling materials. Workers in a trench must stand clear of pipe being lowered and of the excavator bucket as it swings, and should be outside the swing radius of the machine when they are on the surface. A pipe lowered on a sling can swing, slip or drop; workers should guide it with tag lines and receive it only when it has been set down or is under control.

The bucket is not a work platform, a man-lift or a means of access, and lifting with an excavator requires a machine rated for lifting, a lift chart, approved attachment points and, in most jurisdictions, an operator trained for lifting. HSE-219 covers rigging and lifting in more detail.

Falls into the excavation

Open excavations are also fall hazards for workers walking past, for equipment operators stepping off machines and for the public. OSHA 1926.501(b)(7) requires each employee at the edge of an excavation 6 ft or more deep to be protected from falling by guardrail systems, fences or barricades when the excavation is not readily seen because of plant growth or another visual barrier, and requires wells, pits and shafts to be guarded. 1926.651(l) requires walkways where employees or equipment cross over excavations, with guardrails where the walkway is 6 ft or more above the lower level.

Protecting the public

Many excavations are dug in streets, sidewalks, yards and parks where the public cannot be expected to recognize the hazard. Children are particularly at risk around open trenches and water-filled holes. Excavations left unattended, especially overnight, should be fenced or covered with steel road plates designed for the traffic, secured against sliding, and lit or marked as needed. Traffic control on public roads follows Part 6 of the Manual on Uniform Traffic Control Devices (MUTCD) and any state supplement.

Adjacent structures

Excavating beside a building, retaining wall, utility pole, sidewalk or road can remove the soil that supports it. The structure may settle, crack or collapse into the trench, and the extra load it places on the excavation can overwhelm a protective system designed without it. Before digging near a structure, the competent person should identify its foundation depth and type, consider whether the excavation will extend below a line drawn down and out from the foundation at a safe slope, and obtain an engineer's design for underpinning, bracing or a supported excavation where needed. Utility poles near trenches may need to be braced or held by the utility before digging.

Housekeeping in and around the trench

Good housekeeping is easy to neglect in an excavation and has a large effect on safety. Tools, offcuts of pipe and fittings, rocks and clods left on the trench floor create tripping hazards in a confined space where workers often look upward at loads and equipment. Loose material at the edge can be kicked or knocked in. Hoses and cables for pumps and saws should be routed so they do not cross access points or snag on equipment. At the end of each shift, the trench floor should be clear, ladders in place, materials stored back from the edge and the excavation secured for the night.