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

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

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

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.

Slippage of material in a trench

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

Undermining of boundary wall

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

Close sheeting in excavation

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

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

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).

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

Barriers around excavation by foot path

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.

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.

Vehicle protection at the top of an excavation

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

Timbered excavation with ladder access and supported services

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.

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

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

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

Entering a confined space

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

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

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.

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.

Training for confined space entry

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.

Emergency escape breathing apparatus.

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

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.