Trench safety

Excavation is an important element of most, if not all, construction projects; from installing utilities to removing old foundations and laying new ones, digging trenches and pits is a task that can’t really be avoided. But there are methods that can be used to ensure that excavations can be carried out in a way that ensures the safety and wellbeing of all involved. If those methods aren’t employed on site, the result can be very serious indeed – and sometimes fatal.

Case study:

A construction company was fined after a worker had to be dug out of a trench that collapsed onto him.

The employee suffered a broken shoulder and collarbone as well as punctures to both of his lungs and fractures to all but two of his ribs.

A trench was being dug with an excavator to help connect the drainage system of the old property with a new extension. The workers found a large boulder in their way that was stopping them from any further digging. They brought in an excavator to move it.

The injured man was trying to help guide the excavator. During this operation, one of the walls of the trench (which was nine feet deep) subsided, burying the worker under the dislodged earth.

Workers immediately started digging the soil away from the man’s head to allow him to breathe. He remained partially buried in the trench until the emergency services arrived and dug him free.

The HSE investigation found that the trench had not been supported or ‘stepped back’, to control the risk of collapse. Nobody had formal health and safety training for managing a construction site and the excavation work had not been risk assessed. As a result, workers were given instructions through verbal briefings rather than detailed, mapped-out planning.

The company pleaded guilty to breaching Sections 2(1) and 33(1)(a) of the Health and Safety at Work etc. Act 1974. The company was fined £14,000.

This case highlights just how dangerous excavations can be. If you are an employer and you have been unable to circumvent the need for actual excavation work, what precautions could you undertake to reduce or even eliminate the risks?

What employers need to do

To make sure that the precautions taken are still effective, the excavation supports or battering should be inspected by a competent person when the shift begins and at other specified times, such as after any event that may have affected their strength or stability, or after a fall of rock or earth. The inspection must be recorded and immediate steps should be taken to correct any faults that are found.

Until it has been confirmed that the excavation is safe, no work should be carried out.

Client/contractor information

If a commercial client has hired a contractor to carry out work which will include excavations, they should provide the contractor with information on ground conditions, underground structures (such as water courses) and the location of services such as water, gas and electricity which may be encountered when excavation work is carried out.

The contractor should make use of the information provided when planning and preparing to undertake excavation work.

Trenchless working

It’s worth taking the time at the design and planning stage to consider whether trenchless techniques can be employed – this will reduce the amount of major excavation and with it, the probability of accident and/or injury.

Temporary support

An assessment of the need for temporary support should be made before any excavation starts and the equipment identified should be available at the start of the job. There will then be no excuse for proceeding with the job in an unsafe fashion because of lack of safety equipment.

Battering the excavation sides

Battering is the construction of a slope up and away from the excavation. Battering the sides of the excavation to a safe angle of repose will increase the safety of the job. The angle of repose is the angle of a slope above which soil will slide downwards. Different soil types will have different angles of repose and conditions will also affect the angle (for wet ground, a much flatter slope will be needed).

Falling or dislodging material

Depending on the distance, loose spoil may slide back down into the excavation. Edge protection should be used to prevent this happening, including:

• toeboards,

• projecting trench sheets,

• box sides.

Head protection should be issued to all workers and steps taken to ensure that it’s worn.

Undermining other structures

Sufficient space should be left between the edges of excavations and

• scaffold footings,

• buried services or

• foundations of nearby buildings or walls.

A structural engineer’s advice may be needed to determine if extra support for the structure is going to be needed whilst the job is carried out.

Effect of plant and vehicles

Plant and vehicles can add a considerable amount of weight to soil that has already been undermined by excavations and should not be parked close to trenches or other such spaces.

Checklists

Managers and supervisors need to keep in mind the following:

1. Make sure workers can get in and out of the excavation easily and safely 2. Provide adequate and sufficient fencing to protect the public and other workers from the excavation 3. Supplement the safe system of work by using information, instruction and training. 4. Ensure that excavations are made safe, by trench supports, battering back, fencing or other equally effective measures 5. Be aware that there is no safe minimum depth of excavation 6. Provide training for your staff which highlights the risks