Toolbox Talk: Excavations

Introduction

Many construction sites require excavation work, particularly trenches. If this work isn't planned or carried out correctly, it may lead to serious injury or death. There are also general hazards around excavations that should be considered on site. These include falls, tripping over equipment, hazardous atmospheres, and falling material.

What is excavation work?

Excavation work generally means work involving the removal of soil or rock/s from a site, (or from an open face, hole, or cavity), by the use of tools, machinery, or explosives.

IDENTIFY buried services

All excavation digging must be planned and carried out correctly to avoid any contact with any underground services.

• Expect to find services at any depth and consult with all service providers/owners to obtain plans showing where buried services may be present.
• Use plans, electronic location devices and hand digging to locate services prior to using mechanical plant.
• Once located, mark out where they are using location devices on the site plan.

Excavation work can occur anywhere, including:

• On construction sites
• On business premises
• In public areas

Excavation work includes:

• Open excavations
• Potholing
• Pit excavations
• Trenches and retaining walls
• Shafts and drives

Is it a HAIL site?

Hazardous materials may be in or on the ground where excavation or trench work is required. In some cases, these properties may be listed on the Hazardous Activities and Industries List (HAIL).

If hazardous materials are suspected or identified, stop work immediately, and seek professional advice.

ASSESS ground stability

While excavations shallower than 1.5 metres may not be considered particularly hazardous, they have been known to collapse, which can in turn lead to serious injury if a worker is in the trench at the time, therefore safety precautions should be considered.

However, excavations that are 1.5 metres or deeper are particularly hazardous. These excavations (where a person is required to work inside, or where there is ground cover overhead) must be notifiable to WorkSafe New Zealand and must be shored unless:

• The face is cut back to a safe slope or benched (with stepped down sides to deal with loose soil) and the material in the face will remain stable under all conditions or work and weather.
• Shoring is impracticable or unreasonable and safety precautions certified by a registered engineer to be adequate, have been taken.
• The type of work and location of workers means there is no actual damage.

MANAGE – Safe slopes or shoring

• Avoid underground services and ensure nearby structures are not undermined - use safe digging practice and dig away from them.
• Check the excavation area each day before starting work and after any event that may affect its stability. A record should be kept of these inspections.
• Provide safe access to get in and out.
• Prevent collapse - shore, bench, or batter back. Do not assume ground will stand unsupported.
• Prevent people and materials falling in - use barriers suitable for the task and strong enough not to collapse if someone falls against them.
• Remember to keep the site, and plant used on site, secure and locked away when the site is not in use.

When shoring is used as a control to manage the critical risk of an excavation, it must be:

• Designed by a suitably qualified professional engineer.
• Made of suitable material of sound quality suitable for and strong enough for the excavation site.
• Constructed with bracings, jacks, and struts to prevent accidental displacement.
• Installed with packings and wedges that are held by nails or spikes.

Quick reminders for using machinery around an excavation site

• Only use equipment you have been trained for and are competent to use.
• Take five minutes at the start of the day to check and record the machine is safe and operational. Check open trenches are stable.
• Ensure you check and locate underground services and mark their location on the ground with fluorescent paint if necessary.
• Avoid being in the trench unless absolutely necessary.
• Work safely around overhead lines; always treat them as live.
• Isolate the work area e.g., using barriers, cones and tape.
• Use a ‘spotter’ and agree on what signals will be used. The operator must stop if the spotter goes out of eyesight.
• Know the machinery limitations; operate it only in accordance with manufacturer's or hirer's instructions.
• Ensure sides of trenches and excavations are stable and well supported.
• When moving machinery between worksites, lower booms, plan the route and use a 'spotter'.
• When machinery is stationary, apply brakes and/or wheel chocks.

Q and A

• Ask your workers, contractors and sub-contractors to identify some of the major hazards around excavations. These could be:
  • The depth of the excavation
  • The soil types
  • Vibration
  • The presence of moisture, rain, or a high-water table level
  • Superimposed loading, or mobile plant working close to the edge of the excavation area.
• Ask workers to discuss shoring methods they've used or seen used before - and then compare them to the list above.