Page 84 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

8 WORKING SAFELY IN

EXCAVATIONS AND CONFINED

SPACES

Every year construction workers are killed and injured when the excavations and
trenches they are working in collapse suddenly. Deaths have occurred in both
shallow and deep excavations, so it is important that any excavation work is
properly planned, managed, supervised and carried out to prevent accidents.

Many types of ground are, to some degree, self-supporting but this should not
be relied upon when working in a trench. It is vital that precautions are taken to
ensure that excavations are adequately supported.

Working in trenches and excavations

Plumbers are fortunate in that the need for working in trenches and excavations
is limited. Most of the outside work below ground is done by others on
construction sites, such as groundworkers and the services providers such as
the gas company or the water authority. The services – i.e. water, gas, building
drainage – that plumbers may have to deal with are relatively shallow, but there
is still a need to understand the planning and working practices of working in
trenches and excavations.

Trenches and excavations

The maximum depth that a trench or excavation can be dug without support
is 1.2 m. On the average person, 1.2 m would be around waist height. The
significance here is that the chest would be above ground level and so breathing
would not be restricted in the event of trench collapse.
After this depth, the trench sides should be either:

● battered – a method by which the sides of the trench are sloped away from
the trench bottom; the angle of the slope would be decided by the type of
ground but usually 45° is considered adequate
● benched – benching simply means that the sides of the trench are cut into
steps away from the trench side
● supported using a proprietary trench support system.
The general requirements for safe trench and excavation design are as follows.

● The ladder used to gain access should be secured in position to the trench
supports, and in long trenches access should be spaced at regular intervals.
● The spoil from the trench should be at least 1 m away from the edge of the
trench to prevent trench collapse; 1 m of earth can weigh as much as a
3
tonne and the added weight against the weak edge of the trench could cause
collapse or earth slide.
● The edge of the trench must have a 2 m-high barrier placed around it, at
least 1 m away from the edge, to stop people from falling into the trench.
It must also have a toe board to stop tools and materials from being
accidentally kicked in.

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