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.

Ontario's O. Reg. 213/91 requires any ladder used to enter a trench to be placed within the area protected by the support system, so that workers never climb out through an unprotected section. Ontario's general ladder rules also apply: the ladder must be secured against movement and should extend about 900 mm above the landing so the worker has something to hold on to while stepping off. Alberta's OHS Code requires a safe means of entry and exit within 8 m of a worker in a trench deeper than 1.5 m, and requires the trench to be supported or sloped so the worker can reach it safely.

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.

Ontario requires a level area at least 1 m wide along the upper edge of each wall to be kept clear of equipment, excavated soil, rock and construction material, and requires stockpiles of material to be placed so they do not affect the stability of the walls. Alberta requires the leading edge of a spoil pile to be at least 1 m from the edge of the excavation, and the slope of the pile to be no steeper than 45 degrees from horizontal.

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.

Ontario prohibits operating or locating vehicles and machines in a way that affects the stability of the excavation walls, and keeps equipment out of the 1 m clear area. Where an operator's view of the edge is limited, a signaller should guide the machine, and stop logs or barricades can mark the limit of approach. Crews should keep track of where trucks back up to be loaded and keep them away from unsupported edges.

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

No worker should be under a load handled by lifting or digging equipment. 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. Ontario's construction regulation prohibits workers from being beneath a suspended load, and these rules apply in and around trenches as much as anywhere else.

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. Ontario requires a barrier at least 1.1 m high at the top of every wall that is not sloped, where a person could fall more than 2.4 m into the excavation. Shorter drops still need control: covers, fencing or clearly marked walkways keep people away from edges. Where workers must cross a trench, a walkway with guardrails is needed rather than a plank across the gap.

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 the provincial manual, such as Ontario Traffic Manual Book 7 for temporary conditions.

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.