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Excavation Hazards and Control Measures
Site excavation is a necessary part of many construction projects, but can be an extremely dangerous job if workers are poorly trained, if the proper safety regulations are not followed, or if the construction company employer or supervisor are in any way negligent.
What is Excavation:
An excavation as any man-made cut, cavity, trench, or depression in the earth’s surface formed by earth removal. Sometime excavation is mixed up with another term ‘trench’ but technically both terms are not identical such as:
A trench is defined as a narrow underground excavation that is deeper than it is wide, and is no wider than 15 feet (4.5 meters).
From 2000 to 2009, an average of 35 workers died every year in trenching or excavation cave-ins, according to Bureau of Labor Statistics data, USA. About three in every four fatalities occurred at residential worksites.
Hazards & Risks Associated With Excavation
Excavation on a construction site requires the use of heavy machinery, proper safety measures, and the careful attention of construction workers and supervisors. Unfortunately, there are a number of factors that can lead to the occurrence of an excavation accident, which can result in serious injury and tragic loss of life. The following are hazards & risks associated with excavation:
- Cave-in or excavation collapses excavated material
- Failure of excavation machinery
- Falling person/objects near excavations
- Slip, Trip & Fall
- Hazardous atmosphere/presence of flammable gases
- Exposure to Underground facilities (electric wires, water/gas pipeline)
- Failure to properly shore an excavation site
- Poor training of construction worker
- Asphyxiation due to material flow
- Flooding/Underground water hazards/Extreme weather conditions
- Animal bites/Dengue virus
Excavation Control Measures
- A competent person who fully understands the dangers and necessary precautions should inspect the area of excavation prior starting work. Tools like geo-scanning detectors, metal/wire detectors or site layouts are used to detect underground utilities.
- Excavations should also be inspected after any event that may have affected their strength or stability, or after a fall of rock or earth.
- Inspection of excavation machinery/equipment must be done to identify any substantial faults prior to start work. A record of the inspections will be required and any faults that are found should be corrected immediately.
Safe Digging Practices:
- Excavation work should be carried out carefully and follow recognized safe digging practices. Once a locating device has been used to determine cable positions and routes, excavation may take place, with trial holes dug using suitable hand tools as necessary to confirm this.
- Excavate alongside the service rather than directly above it. Final exposure of the service by horizontal digging is recommended, as the force applied to hand tools can be controlled more effectively. Insulated tools should be used when hand digging near electric cables
- Gas testing must be done before & during the entire activity to measure O2 level and to find out the presence of other hazardous gases. The testing must be done by authorized person.
Protection to Fall into Excavations:
Edges of excavations should be protected with substantial barriers where people/object/equipment are liable to fall into them.
It can be done by:
- 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
- The support system itself, e.g. using trench box extensions or trench sheets longer than the trench depth
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.
- 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.
- 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.
Preventing Excavations Collapse:
- 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, baulks etc.) are available on site before work starts.
- Battering the excavation sides – Battering the excavation sides to a safe angle of repose may also make the excavation safer. In granular soils, the angle of slope should be less than the natural angle of repose of the material being excavated. In wet ground a considerably flatter slope will be required.
Training & Supervision & Safe Systems of Work:
- Worker must provide adequate training on Work at height, scaffolding, tools & machine operations. Activities related to excavation must be supervised e.g. provision of banks-men to guide the vehicles.
- Develop safe system of work and introduce permit to work system to carry out the activity in safe manners.
Methods for Groundwater Controlling and Dewatering:
- Sump pumping
- Well point system
- Siphon draining
- Deep well system
- Ejector system
- Safety signs must be displayed on site & they should be clearly visible and understandable
- Use luminous & reflective safety signs during low visibility or at night to prominent the hazards.
Extreme Weather Conditions:
- Workers must be provided with frequent rest breaks & job rotations. Provision of Cooling shelters, drinks & light clothing for hot environment and warm foods, insulating clothes for cold environment. In case of stormy weather or rain activity must be stopped immediately.
- Provide cover & brick edges around small excavation & trench to avoid sliding down of water during rain into excavations.
FREE Rescue Plan:
- Develop fire emergency plan and provide suitable fire equipment on site (Fire blanket, fire extinguisher, sand buckets & fire retardant suits)
Personal Protective Equipment:
- Provide adequate PPEs like hard helmet, visibility vest, hard/slip resistance shoes, respiratory equipment, fall arrest or harness, safety goggles, Face shield & Hard/insulating gloves.
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