Excavation and Trench Safety Toolbox Talk

In Ajax, Ontario, six workers were installing a storm sewer catch basin for a road widening project when the north wall of the excavation collapsed with four of them inside. Two workers died and two were injured. Investigators found a weak soil layer that needed shoring or sloping, but there was no support system and no engineer's opinion on the wall. The contractor pleaded guilty and was fined $250,000 in November 2024.

Source: Ontario Ministry of Labour, Immigration, Training and Skills Development

1. Trenches deeper than 1.2 m need shoring, sloping or a trench box (1.5 m in Alberta and Manitoba). Check your provincial regulator.
2. Shallow trenches kill too. A worker kneeling or bent over in a waist deep trench can be buried by one slab of the wall.
3. A competent person inspects the excavation before each shift and after rain or any change.
4. Shoring and trench boxes only work if they are installed the way they were designed. No missing struts, no gaps, and no digging below the bottom of the box beyond its rating.
5. Keep spoil, materials and equipment at least 1 m back from the edge, more in loose ground.
6. Check for underground services before digging. Never assume the plans are exact.
7. Provide a safe way in and out, such as a ladder secured at the top, close to where people work.
8. Never ride the bucket or climb the shoring to get in or out.
9. Put barriers around the excavation so people and vehicles cannot fall in.
10. Rain, water, vibration and nearby traffic weaken the walls. Watch for cracks, bulging and falling soil.
11. Keep water out of the trench. Pump it out and do not work in a trench with water building up unless it has extra protection.
12. Deep trenches can collect dangerous gases. Test the air if there is any doubt.
13. If the trench starts to collapse, get out and stay out. Rescue only with proper support in place.

1. How deep is our excavation today, and what support is in place?
2. Who inspected it this morning?
3. Where is the ladder or way out?
4. What signs would tell you the walls are moving?
5. What would we do if someone was buried, and who would we call?

• Run the talk at the edge of the actual excavation, standing well back from the lip.
• Measure the depth together and agree what protection that depth needs.
• Point out the spoil pile, the ladder or ramp, and any cracks, water or vibration sources.
• Show the competent person's inspection record for today.
• Agree the emergency plan for a collapse and who calls for help.
• Record attendance, depth and protection on the sign-in sheet.

In Ontario and British Columbia, workers must not enter an excavation deeper than 1.2 metres unless its walls are sloped, shored or protected by a trench box, or it is cut in solid rock. In Alberta the trigger is 1.5 metres: the employer must cut back the walls, install a temporary protective structure, or both before work starts. Check your own province, because the details differ.

Source: Government of Ontario