1. BET2492/BPS3413 CONSTRUCTION SAFETY
Lecture 7 : Excavation Works and Confined Spaces

2. LEARNING OUTCOMES
Upon completion of the class, it is expected that student will be able to:
LO1: Identify hazards on excavation works
LO2: Determine suitable controls when performing excavation works
LO3: Identify hazards on confined spaces
LO4: Determine suitable controls when working in confined spaces

3. EXCAVATION WORKS - INTRODUCTION
Essential part of the construction process and one of the most hazardous
Example of work that requires excavation – building foundations and the installation of drainage, sewage and other services

4. EXCAVATION – HAZARD AND CONTROL
Accidents and injury due to work in excavations are often related to the composition and structure of the soil - the walls of the excavation.
Many types of soil, such as clays, are self-supporting but others, such as sands and gravel, are not.
The walls of excavations can collapse without any warning resulting in death or serious injury.

5. Slippage of material in a trench

6. EXCAVATION HAZARDS
The specific hazards associated with excavations are as follows:
collapse of the sides
materials falling on workers in the excavation
dangers associated with excavation machinery
falls of people and/or vehicles into the excavation
workers being struck by plant
specialist equipment such as pneumatic drills
hazardous substances particularly near the site of current or former industrial processes
influx of ground or surface water and entrapment in silt or mud
proximity of stored materials, waste materials or plant
proximity of adjacent buildings or structures and their stability
contact with underground services
contact with overhead power lines
access and egress to the excavation
fumes, lack of oxygen and other health hazards

7. Undermining of boundary wall

8. EXCAVATION WORKS
Most critical factors to be considered when planning an excavation - the nature of the soil which is to be excavated
All excavations, except the most shallow, need some support using trench sheeting
When excavation work takes place in non-cohesive soil (e.g. sand, gravels and soft clays), close sheeting will be required to prevent ground movement
Cohesive soils, such as most clays and rock, some support, use open sheeting

9. Close sheeting in excavation

10. PLANNING EXCAVATION WORKS
Address all significant hazards:
collapse of the sides
control of people and vehicles around the surface area of the excavation
the proximity of adjacent structures
the position of any underground services
access to the excavation
the protection of members of the public
Conduct site survey
Pipe or cables should be identified and isolated before work begins

11. PLANNING EXCAVATION WORKS
Organized meetings with occupants of surrounding buildings
Ensure enough trained and competent workers, supervisors and materials for support
Special PPE and safety signs should be delivered and made available on site
Proper induction to subcontractors – hazards and safety precautions
Ensure all equipment and material use for excavation work are safe

12. RISK ASSESSMENT
Risk assessment should be made by the contractor before work begins
Purpose: to identify potential hazards and determine the control measures required
The significant findings are recorded in a method statement
Method statement – describe the plant, equipment and the safe methods of working required to control the risks generated
Provide information on hazards identified:
the nature of the ground, soil structure and groundwater regime
the depth of excavation
the nature of the work required to be undertaken within an excavation
the location of the work (e.g. readily accessible public place, contaminated ground or heavily serviced urban area).

13. METHOD OF STATEMENT
Contain information about the necessary emergency arrangements:
Details regarding any site-based personnel trained to administer first aid
The location of the nearest hospital with accident and emergency facilities
The risk assessment also needs to categorize the level of risk
High risks -- the collapse of the excavation walls, contact with existing underground or overhead services, plant and materials falling into excavations and the presence of hazardous atmospheres and contaminated soil.
Medium risks -- The possibility of persons falling into the excavations
Low risks -- flooding of excavations

14. Barriers around excavation by foot path

15. PRECAUTIONS AND CONTROL
Excavations must be fenced and suitable notices are posted around work site
First form of control - to decide whether the excavation is necessary
May use new technology to eliminate excavation works (trenchless technologies)
Example:
micro-tunneling
directional drilling
impact moling
auger boring
pipe relining
pipe bursting.

16. EXCAVATION PRECAUTIONS
A competent person must supervise the work
The walls of the excavation trench must be prevented from collapsing by digging them at a safe angle or by shoring them up with timber, sheeting or a proprietary support system.
Workers must wear hard hats and safety footwear
Workers should never enter an unsupported excavations or work ahead of supports
The excavation site must be well lit at night
Personal protective equipment (gloves, overalls, boots, ear defenders and hard hats) must be worn by operators of noisy plant
Safe access by ladders is essential as are crossing points for pedestrians and vehicles.

17. Vehicle protection at the top of an excavation

18. Trench sheets with timber walings, screw props, puncheons and sole plates.

19. Timbered excavation with ladder access and supported services

20. INSPECTION REQUIREMENTS
The duty to inspect and prepare a report only applies to excavations which need to be supported to prevent accidental fall of material.
Only persons with a recognized and relevant competence should carry out the inspection and write the report
Inspections should take place at the following timing and frequency:
after any event likely to affect the strength or stability of the excavation
before work at the start of every shift
after an accidental fall of any material.

21. CONFINED SPACES - INTRODUCTION
Work should only take place in a confined space if it is unavoidable
Workers in confined spaces should be skilled and trained or specialist contractors
Definition of confined spaces - any space of an enclosed nature which has limited means of access and egress, restricted natural ventilation and is not intended for continual occupancy by persons

22. EXAMPLES OF CONFINED SPACE
Manholes
Trenches
Combustion chambers in furnaces
Sewers
Ducts
Chambers
Tunnels
Some unventilated areas
Vats
Excavations
Rooms within buildings (particularly below ground level)
Silos
Storage tanks
Holds of ships
Wells
Pits
Boilers

23. CONFINED SPACES HAZARDS
The difficult access and egress – entrapment, escape and rescue more problematic
free flowing solid such as grain in a silo
electrocution from unsuitable equipment
difficulties of rescuing injured personnel
The accumulation of vapours, gases or fumes and the lack of ventilation
drowning due to flooding
asphyxiation due to oxygen depletion
fumes from plant or processes entering confined spaces
poisoning by toxic substance or fumes
excessive heat leading to heat stress
explosions due to gases, vapours, and dust
claustrophobic effects due to restricted space
fire due to flammable liquids, vapours and oxygen enrichment
diseases from animal wastes, infected materials or micro-organisms,
fall of materials leading to possible head injuries

24. Entering a confined space

25. RISK ASSESSMENT
Essential requirement of the Confined Spaces Regulations
Must be done so that a safe system of work may be determined
Identify the hazards present in the confined space, assess the risks and determine suitable controls to address those risks
Must be done by a competent person

26. RISK ASSESSMENT Examination and investigation of the following items:
the use of cleaning chemicals and their direct effect or interaction with other substances
any previous contents in the confined space
any sources of ignition for flammable dusts, gases, vapours, plastics etc.
any residues that have been left in the confined space (sludge, rust or scale, and details of gases or vapours)
the need to isolate the confined space from outside services or from substances held inside such as liquids, gases, steam, water, fire extinguishing media, exhaust gases, raw materials and energy sources
any contamination from adjacent plant, processes, services, pipes or surrounding land, soil or strata
the requirement for emergency rescue arrangements including trained people and equipment.
any oxygen deficiency and enrichment
the physical dimensions and layout of the space since these can affect air quality

27. METHOD STATEMENT
Consists of method details, plant and equipment to be used, general precautions and any special requirements for dealing with health hazards, and the sequencing of work.
The details and procedures required for any permit to work systems should also be included.

28. CONTROL AND PRECAUTIONS
Avoid the need for employees or others to enter a confined space
If entry is unavoidable, employer should ensure that a safe system of work is available and that adequate emergency rescue arrangements are in place
Site supervisor must ensure that all necessary equipment is available on site in accordance with the risk assessment, method statement and any other planned procedures, such as a permit to work, before any person is allowed to enter a confined space
All safety equipment must be regularly checked and maintained
Specific, detailed and frequent training is necessary for all people concerned with confined spaces such as rescuers, supervisors or those working inside the confined space.

29. Training for confined space entry

30. MONITORING ARRANGEMENTS
Before any work commences in the confined space, the site supervisor must arrange for any necessary environmental surveys and sampling needed to protect the health of the workforce
Continuous gas monitoring using electronic instruments should be used
The workforce should also be given health checks periodically – ensure they are not suffering any claustrophobic effects or problems with the wearing of breathing apparatus.

31. Emergency escape breathing apparatus.

32. EMERGENCY ARRANGEMENTS
Set up contingency plans to deal with an emergency in the confined space.
Include details of rescue teams together with individual responsibilities
The contact names and telephone numbers of the local emergency services
Details of the communication arrangements from inside the confined space
The provision and maintenance of the rescue and resuscitation equipment
The raising of the alarm, alerting the rescue team and maintaining close supervision of the workforce inside the confined space
The notification of and consultation with the emergency services
The protection and safeguarding of the rescue team

33. EMERGENCY ARRANGEMENTS
The fire safety precautions and procedures
The provision and maintenance of fire fighting equipment
The control and possibly the protection of adjacent buildings, plant and equipment
The arrangements for dealing with emergencies outside the normal working day
The first aid arrangements including any special training required of first aiders
The training of rescuers and simulations of emergencies, such as fire drills
The size of access openings to permit rescue with full breathing apparatus, harnesses, fall arrest gear and lifelines.