Trench, Block Stack and Inspection Pressure
At a school boundary-wall project in Sunyani, a 1.4 m deep foundation trench has been dug through sandy clay. Overnight rain has left standing water in the trench, and spoil is banked about 0.8 m from the edge. No trench inspection has been recorded since the rain. Two workers are preparing to enter without shoring; one says the trench 'looked fine yesterday.' Nearby, a delivery truck has stacked 6-inch sandcrete blocks 2.2 m high, and a labourer wants to climb the stack to guide the truck. Only one helmet is on site, and a mixer is being cleaned by a worker in open sandals. Cement dust is visible. The foreman says the client's inspection is at 3 p.m. and work must continue. You are the site supervisor.
1. Identify the hazards that justify an immediate stop-work instruction and rank them. Explain your ranking.
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The hazards that justify stopping work are:
- Unsupported trench with water and surcharge - this is the highest risk. A 1.4 m trench in sandy clay after rain can collapse without warning, and the spoil bank 0.8 m from the edge adds load to the trench wall. A collapse would bury a worker completely, so potential severity is fatal.
- Unstable block stack used as a working platform - the stack is 2.2 m high and a labourer plans to climb it. A fall or toppling stack could cause serious injury or death, and the stack is also close to vehicle movement.
- Poor personal protection and cement dust exposure - open sandals, only one helmet, and visible cement dust create foot, head and respiratory risks, but these are usually controlled before work rather than being an immediate life-threatening condition.
The ranking follows likely severity and number of people exposed: trench collapse first, block-stack fall second, general PPE and dust third. The foreman's inspection deadline does not change the ranking.
2. Set out the immediate controls you would apply before any work resumes, using the hierarchy of control.
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Apply controls from the most reliable downward:
- Eliminate: stop all entry into the trench and stop the block offloading near the trench edge. Move workers to a safe assembly point.
- Engineering controls: pump out or drain the standing water; batter back the trench sides to a safe slope or install proper shoring; move the spoil bank and block stack at least 1 m from the edge, preferably further; provide safe ladder access; barricade the trench.
- Administrative controls: a competent person must inspect the trench after the rain and before re-entry, and record the inspection. Hold a toolbox talk on trench entry, block stacking and cement dust. Set a maximum stack height and a no-climbing rule. Provide water for washing cement from skin.
- PPE: issue helmets, safety footwear, eye protection and suitable respiratory protection for dusty mixing. PPE is last because it does not prevent trench collapse or stack failure.
Work should not resume until the trench is dewatered, supported or battered, inspected and recorded.
3. The foreman insists the inspection must go ahead and asks you to 'just sign the trench off'. How do you respond, and what records do you make?
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I would refuse to sign. Signing would falsely certify that the trench is safe and would transfer responsibility for an uncontrolled collapse risk. I would tell the foreman plainly that the inspection can proceed only after the trench is made safe; the client can inspect the wall layout, blockwork or other completed work away from the trench in the meantime.
Records to make:
- a stop-work or hazard notice stating the date, time, location and the specific defects: water, unsupported sides, spoil within 0.8 m, no inspection record, block stack height and climbing;
- the control measures required and the name of the person responsible;
- a trench inspection record completed by a competent person after the controls are in place;
- a brief note of the foreman's instruction and your refusal, copied to the site manager or contractor;
- a toolbox talk attendance record for the workers.
The aim is to protect workers and to leave evidence that the decision was based on risk, not on obstructiveness.