Excavation - Hazards and its Control Measures

EXCAVATION:

 An Excavation is any man made cut, cavity, trench or depression in the earth's surface formed by earth removal.

EXCAVATION TYPES:

1. OPEN - Large and Sometimes deep excavations

2. Trenches - Linear Excavations for utilities or footings

3. Pits - Excavations for footing of one column, elevator shaft.

EXCAVATION WORK HAZARDS:

1. COLLAPSE

When the unsupported side of the excavation slip and cave in. Severe crush injuries can result from even relatively small collapses because soil is very heavy. Workers buried or entrapped in soil can asphyxiate in minutes. Workers do not have to be completely buried for asphyxiation to occur; being buried to the chest will lock the rib cage have the same effect.

2. STRIKING BURIED SERVICES:

When high voltage electrical cables, gas pipes, mains pipes or other buried services are struck during the excavation work. This can lead to electrical arcing, shock, burns and fire or gas explosion or rapid flooding of the excavation, not to maintain major business disruptions to service users.

3. PEOPLE FALLING IN

When People fall in to the excavation from an unfenced edge or whilst climbing into or out of the excavation from ladders.

4. OBJECTS FALLING IN

When tools or materials fall from an unprotected edge into the excavation and onto occupants

• Vehicles driving close to the side of the excavation
• Soil (loose soil) piled close to the sides of the excavation 

5. FLOODING

From surface water during heavy rain, ground water or a ruptured water main.

6. HAZARDOUS SUBSTANCES

The ground surrounding the excavation may contain methane or hydrogen sulphide that can leach out of the soil and into the excavation, or be contaminated with hazardous materials which have containment the land  due to previous activities.

7. COLLAPSE OF ADJACENT STRUCTURES

In digging an excavation the foundations of nearby buildings may be distributed, resulting in the destabilizing or collapse of the structure.

CONTROL MEASURES FOR EXCAVATION HAZARDS:

1. BATTERING

The sides of the excavation can be sloped back, battered at an angle that is sufficiently shallow that the soil will not slip.

2. SHORING:

The sides of the excavation can be supported (shored) with metal or timber that is fixed in place inside the excavation.

3. SHIELDING / TRENCH BOX

The side of the excavation can be temporarily supported by a metal box that can be lifted into the excavation and moved along to give a protected work area.

4. LOOSE MATERIALS

May fall from soil 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.

5. UNDERMINING OTHER STRUCTURES

Check that excavations do not undermine scaffolding 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.

6. 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.

7. PREVENT PEOPLE FROM FALLING

Edges of excavations should be protected with substantial barriers where people are liable to fall into them.

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