EXCAVATION :Every year several people are killed or seriously injured

1) Introduction :-

 Every year several people are killed or seriously injured by collapses and falling materials while working in excavations. They are at risk from:

(a) Excavations collapsing and burying or injuring people working in them;

 (b) Material falling from the sides into any excavation; and

(c) People or plant falling into excavations…etc.

We are responsible to prevent danger to workers in or near excavations. Please note that this bulletin is a brief description about this subject and not the exhaustive list of control measures for excavation

(2) Planning of Excavation Works

We can avoid the accident at the excavations if we plan the excavation work properly from the beginning. Even a small excavation of depth of 1.5 mtr deep can lead to fatality in the absence of safety precautions. Excavation work has to be properly planned, managed, supervised and carried out to prevent accidents.

(3) The following are the general & common safety measures with regard to the excavation

 Collapse of excavations :- 

Ø Temporary support – Before digging any trench pit, tunnel, or other excavations, decide what temporary support will be required and plan the precautions to be taken. Make sure the equipment and precautions needed (trench sheets, props, etc) are available on site before work starts. As per Dubai municipality’s code of construction safety practice, excavation greater than 1.25 meter deep shall not be permitted unless a shoring system is provided. 

Ø Battering the excavation sides – Battering the excavation sides to a safe angle of repose may also make the excavation safer. This depends on the types of soil.

 Angle of Repose (or Incline) is the angle from the horizontal surface at which the excavation wall is cut.

As per Dubai municipailty’s code of construction safety practice- In open excavations, the angle of repose shall not be more than 40 ◦ unless the stability of an excavation sides at a higher slopes is determined by a professional organisation and approved by the specialised department.

Shoring shall be provided at a workplace where any excavation or earthwork is being performed and there is a risk to the health and safety of a person from the fall or dislodgement of earth, rock or other material that forms the side of the excavation or earthwork or is adjacent to the excavation or earthwork .

 Falling or dislodging material

Loose materials may fall from spoil heaps into the excavation. Edge protection should include toe boards or other means, such as projecting trench sheets or box sides to protect against falling materials. Head protection should be worn. Excavated materials shall be placed atleast 1.0 mtr away from the edge of excavation and shall not be accumulated higher than 1.5 times of this distance.

Remember: 

 No ground can be relied upon to stand unsupported in all circumstances.

  One cubic metre of soil can weigh as much as one tonne. 

Ø Undermining other structures – Check that excavations do not undermine scaffold footings, buried services or the foundations of nearby buildings or walls. Decide if extra support for the structure is needed before you start. Surveys of the foundations and the advice of a structural engineer may be required.

Ø Effect of plant and vehicles – Do not park plant and vehicles close to the sides of excavations. The extra loadings can make the sides of excavations more likely to collapse.

 Falling into excavations

 Ø Prevent people from falling – Edges of excavations should be protected with substantial barriers where people are liable to fall into them. It can be through the provision of Guard rails and toe boards inserted into the ground immediately next to the supported excavation side or fabricated guard rail assemblies that connect to the sides of the trench box or the support system itself, e.g. using trench box extensions or trench sheets longer than the trench depth.

(4) Inspection

A competent person who fully understands the dangers and necessary precautions should inspect the excavation at the start of each shift. Excavations should also be inspected after any event that may have affected their strength or stability, or after a fall of rock or earth. Any faults that are found should be corrected immediately.

(5) Before commencing the work and during the work ,you should consider the following: (Yes/No)

Have you determined the exact location of underground services such as electricity, gas, water and sewerage or the presence of naturally occurring hazards?

Have you ensured the stability of buildings, structures and roads adjacent to the excavation?

Have you organised to isolate the excavation from access by the public by using barricades, covers or fencing?

Will there be adequate support for the excavation, or will it be sloped or battered back to a safe angle?

Is a safe method used for putting in the support, without people working in an unsupported excavation?

Soil shall be removed to a safe distance from the trench edge to prevent collapse into the trench (the distance required will depend on the nature of the soil)?

Materials and plant shall be stored away from the edge of the excavation to reduce the chance of collapse?

Are there established traffic controls where required using adequate signage, personnel and lighting?

Have you ensured safe access and egress in excavations where people are required to enter (sufficiently long secured ladders installed at each end and placed at appropriate distances along the excavation)?

Do you ensure that PPE including hard hat and safety shoes are worn by all entering the excavation?

Are high visibility vests or clothing provided and worn by all exposed to vehicular traffic?

Is the excavation regularly inspected by a competent person (at the start of each shift before work begins or after any event likely to have affected the strength or stability of the excavation)?