Excavations

One of the dangers of an excavation is the possibility of its sides collapsing. One way of preventing this is to install supports of one kind or another. The decision as to whether supports are needed is through risk assessment.

Before starting excavation work it is important to decide what temporary supports will be required for the excavation. Also give consideration to precautions needed to:
·    Prevent collapse of the sides
·    Materials falling onto people in the excavation
·    People and vehicles falling in to the excavation
·    Undermining nearby structures
·    Avoiding striking underground service

Collapse of the sides – three approaches can be used:
·    ‘Batter’ (sloping) the sides of the excavation to a safe angle
·    Step the sides
·    Where the excavation has vertical walls suitable supports needed to be installed by a competent person. Where this system is used the excavation must be inspected before the start of each shift.

Other Hazards that need to be considered include:
·    Materials falling in
     1.    Spoil and vehicles should be kept well away from the edge of the excavation
     2.    Loose material may be kicked in so toe boards should be considered
     3.    Personnel in the excavation should wear hard hats
     4.    People and vehicles falling in
     5.    People – fit guard rails and toe boards along the edges
    6.    Vehicles – use timber baulks or other barriers to keep heavy vehicle away from the edge. Where lighter vehicles are to be used to tip material into the excavation wheel stops should be used.

·    Undermining structures
Before digging starts decide if a structure will need to be supported. Surveys of the foundations and the advice of a structural engineer may be needed.

·    Access / Egress into the excavation
Ensure that sufficient access / egress points with ladders or other means of safe entry are in place. If insufficient access / egress points are not provided employees may be tempted to climb in and out on the supports. Good access and egress is required legally and is important in emergency situations.

·    Fumes
1.    Contaminated ground may lead to gases accumulating in an excavation. A ground condition survey  may need to be carried out to assess this potential. Where there is a potential for fumes to accumulate suitable precautions need to be taken to keep people safe.
2.    Heavier than air toxic gases such as carbon monoxide produced by petrol/diesel engines may start to fill the excavation. Equipment that produces this gas should be kept away. Gas lighting should not be used in excavations because of the risk of explosion should equipment leak gas.

·    Striking underground services
Contact with underground services can be avoided by using:
      1.    Cable and other service plans
      2.    Cable and service locating instruments
     3.    Employing safe digging practices : Hand dig trial hole, use spades and shovels as opposed to picks and forks
     4.    Support exposed service pipes that are likely to break under their own weight once exposed.

A competent person, before the start of every shift, must inspect a supported excavation. A record of an inspection must be entered into a register every week. The excavation must also be inspected after any event that could affect its integrity. This includes falls of rock/earth and adverse weather.