Introduction
Demolition is the most dangerous construction. It is carried out in a structure that has been weakened either as part of the ongoing operation, or as the result of natural forces (storms, floods), fire, explosions or simple wear and tear. The hazards during demolition are falls, being struck or buried in falling material or by the unintentional collapse of the structure, noise, vibration, and dust. In addition workers may be exposed to hazardous chemical and biological agents. One of the biggest challenges is to plan, organise and conduct the work in such a manner that no part of the structure can collapse unexpectedly. The article looks at typical problems in this sector, and presents prevention and control measures.
Definitions and descriptions
Demolition in the construction sector means the bringing down of buildings and other structures that are load-bearing or otherwise related to the physical integrity of the structure. [1] Demolition is often done in combination with site clearing i.e. disposing of the rubble and waste material. In the NACE (revision II) concept, demolition is a subcategory of construction, listed as specialised construction activities (Division F-43) further subdivided into Demolition and site preparation (Group: F-43.1) - indicating that demolition may precede the building of new structures - and having finally the lowest possible subcategory: Demolition (Class: C-43.11).
As a demolition and the following site clearance may involve unearthing the foundations, also excavation activities may play a role.
Dismantling is seen as a partial demolition, i.e. the removal of a component of a structure often with a replacement by a new part (e.g. exchange of boilers).
A relatively new term is deconstruction, meaning to take a building or structure apart in order to preserve valuable elements for re-use (“green demolition"). [2]
There are three principal ways of demolition: take the structure down piecemeal; knock it or push it down; or blast it down using explosives. The choice of method is dictated by the condition of the structure, its surroundings, the reasons for the demolition and cost. Use of explosives will usually be the fastest way of demolition but may not be possible when other buildings are close by. In case demolition must not generate dust and noise usually manual processes will be applied.[3]
Statistics
According to Eurostat in the year 2006 the activities “demolition and wrecking of buildings; earth moving" (NACE revision 1.1 class within the group 45.1) were conducted by 104,000 enterprises which employed 416,700 persons in the EU-27. [4]
In a research study for the UK Health and Safety Executive (HSE) the authors noted that there are hardly accident figures for this specific sector available but concluded that provisional accident statistics provided by the HSE show that 40.6% of construction fatalities occurred on refurbishment sites. Whereby refurbishment includes demolition and dismantling but comprises also of renovation and restoration works.[5]
The German Federal Institute for Occupational Safety and Health BAuA (Bundesanstalt für Arbeitsschutz und Arbeitsmedizin) found as a result of their surveys that the risk for a fatal accident is 15 times higher during demolition work as compared to the remaining construction sector.[6]
Legal requirements
The general OSH framework directive as well as several of the daughter directives are applicable, specifically:
The Directive 92/57/EEC of 24 June 1992 on the implementation of minimum safety and health requirements at temporary or mobile construction sites request all responsible persons to establish a chain of responsibility linking all the parties involved, i.e. building owners, clients, contractors and sub-contractors. In specific cases the competent authorities have to be notified before work can start. The client or project supervisor nominates person(s) responsible for the coordination of health and safety at sites where several firms are present. A health and safety plan has to be drawn up. Dismantling and demolition both fall into the category mentioned in annex II of work involving particular risks to the safety and health of workers. The European Commission, Directorate General Employment and Social Affairs (DG Employment) has published a guide to good practice to assist in applying this directive.[7]
Other important directives include:
- Directive 2009/148/EC - exposure to asbestos at work
- Directive 2003/10/EC - noise
- Directive 2002/44/EC - vibration
- Directive 2000/54/EC - biological agents at work
- Directive 90/269/EEC - manual handling of loads
- Directive 93/15/EEC and directive 2008/43/EC, amended by Directive 2012/4/EU - explosives for civil uses
The most important hazards and risks
Demolition needs to be planned as carefully as any other construction process. The structure to be demolished should be thoroughly surveyed and any drawings obtained, so that as much information as possible on the nature of the structure, its method of construction and materials is available to the demolition contractor. Asbestos is commonly found in buildings and other structures that are to be demolished and requires contractors or sub-contractors who are specialists in handling it.[8]
Companies have to manage the risks associated with demolition work, and the first step of the responsible persons should be to identify the hazards. There are some general hazards and some special work-related hazards.
General hazards include:
- There are often several companies involved in larger demolition work: the client, the contractors and often specialised sub-contractors (e.g. asbestos removal specialists). Communication problems in usually very unclear sites can put workers at high risk of falling from height, being hit by objects, getting buried by collapsing elements etc.
- Instable structures either as part of the ongoing demolition or excavation operations, or as the result of natural forces (storms, floods), fire, explosions, or simple wear and tear. The structures may collapse unexpectedly and bury workers. There can be falling objects (smaller or even larger parts of the building, tools, etc.). Tensions in the structures or in certain objects may be released unexpectedly and exert great forces.
- The building, the structure or the ground may contain more or less hidden various hazardous agents, such as asbestos, PCBs, wood preservatives, mould, dead bodies/excreta from various species like rats, pigeons, bats. For example asbestos and PCBs may cause cancer, and bites from bats may cause rabies.
- Services including the supply of gas, water, sewerage, electricity, fuel and refrigerant in pipes may not have been cut off properly. Accidentally damaging the lines may cause electric shock, burns, fires etc.
Work related hazards include:
- Dust raised by the demolition work.
- Noise and vibration caused by the machines, hand-tools, explosives, and falling/collapsing parts of the building.
- Coldness, heat, and ultraviolet rays from the sun, as a great deal of the work has to be done in the open.
- When taking the building down bit by bit, workers would have to do arduous manual work often at elevated levels. This includes hazards such as falls from height, slip, trips and falls, electric hazards, heavy loads, constrained postures, fires and explosions while operating gas cutters, oxygen lances and similar equipment.
- Knocking or pushing down a building is normally done by using an excavator or other heavy machines. These can be become instable because of overloads or uneven ground, wire ropes may break or appliances such as a demolition ball may get trapped and trying to extricate it can be a very dangerous exercise especially when it requires a worker to climb up. Hydraulic equipment is under great pressure and failing system components can cause severe injuries.
- Using explosives may affect a wide area. There is the possibility of charges that have not gone off and the structure may not have collapsed the way it was planned and is left hanging in a dangerous state of instability.
Demolition workers can be exposed to numerous hazards that may cause serious accidents such as being buried by heavy building parts, falls from height or being hit by breaking wire ropes under excess loads. They can also be exposed to several agents and conditions that can trigger chronic diseases such as cancer byasbestos, silica dust, PCBs, dust and ultraviolet rays, MSD by working with heavy machines and carrying heavy loads.
Generally, workers engaged in dismantling face the same hazards of falling, things falling on them, noise, vibration, dust and harmful substances that are met in demolition work. Contractors who carry out dismantling require a sound knowledge of structures to ensure that they are taken apart in a sequence that does not cause a sudden and unexpected collapse of the main structure. Also excavating has comparable hazards, e.g. collapsing trenches. Ground is notoriously unpredictable; it can be caused to slip by rain, frost or vibration from other construction activities nearby. It may dry out and crack when exposed to the air. A cubic metre of earth weighs more than 1 tonne; a worker struck by only a small fall of ground risks broken limbs, crushed internal organs and suffocation.
Prevention and control measures
After the hazards have been identified, the next step is to analyse the work processes and to determine who will be exposed to these hazards and to what extent. This will then lead to the identification of the necessary prevention and control measures including the reassessment of the effectiveness of the already existing measures. The selection of measures has to follow a certain hierarchy to ensure that the most effective measures like avoidance and substitution are considered first and the least effective ones such as personal protective equipment are seen as the last resort. It is advisable to involve the workers into this risk assessment process as they have very sound knowledge about the conditions and risks at their workplaces.
A systematic approach is necessary from the very beginning of a demolition project. This includes:
- Assign clear responsibilities and appoint a health and safety co-ordinator.
- Employ, contract or sub-contract competent and qualified workers and firms.
- Install a straightforward two-way communication system.
- Plan the necessary training and instruction sessions.
- Collect plans and reports of the structure to be demolished (e.g. stability, connections, where has asbestos been used).
- Conduct surveys to fully evaluate the project, e.g. look at the need for temporary protective structures, check the location of live services, deal with environmental hazards and disposal, utility disconnects, fire protection, first aid services, and project site access.
- Plan the methods and materials needed to conduct the project.
- Plan an effective site management that keeps workers and the public as far away from the risks as possible.
- Discuss the plans with all stakeholders, contractors and sub-contractors. Agree on a plan and issue it to all involved in the project.
- Organise worker involvement.
Several institutions such as the European Demolition Association[9], Government agencies[6] [10] and insurance associations[11] have established safety guidelines and training manuals. The following paragraphs give an overview what measures could be considered in demolition, dismantling and excavation work (adapted from [12] [6] [13] [1] [11] [14] [15] [16]).
Structure stability
The planning has to identify the work sequence required to prevent an accidental collapse. The weight of removed material or machinery on floors above ground level has also to be considered. There should be suitable openings for chuting of debris, so they can be removed continuously. The structure should be maintained in a safe and structurally stable condition. Temporary braces, propping, shoring or guys may need to be added temporarily. The depth and type of foundations, wells and underground storage tanks should also be determined as should the contents of any storage tanks. Adjoining properties and structures also need to be considered.
Hazardous agents
Hazardous chemical and biological agents being part of the building
Asbestos can be present in older buildings as insulation material (pipes, valves, boilers, window boxes etc.), as ceiling tiles, in doors, on roofs, facades. It should be assumed that asbestos is present unless proved otherwise. If asbestos is there specialised companies have to be involved in the removal and safe disposal.
Polychlorinated biphenyls (PCBs) exposure is possible when dismantling electrical capacitors and transformers or when cleaning up spills and leaks of these. It has to be ensured that any spillage does not contact workers and is appropriately cleaned up and disposed of. Also elastic sealants and paints in old buildings may contain PCBs. Any equipment or parts containing PCBs should be handled by qualified workers.
Lead is found in paint, old water pipes and other plumbing fittings, sheets, solders, lead flashing, lead light windows and glass. If it is suspected that the structure contains lead based paint, a test for the presence of lead should be conducted. The precautions which should be taken when demolishing materials containing lead include: minimising the generation of lead dust and fumes, cleaning work areas properly during and after work, wearing the appropriate PPE. Similar measures should be taken for anticorrosion paints containing chromium VI.
Mould and especially their spores can be sensitising. Exposure can be high for specific work processes such as chiselling. In this case whole body protecting clothes and respiratory equipment would be necessary.
Excreta from pigeons, rats etc. can have negative health effects on workers. Care must be taken not to raise dust. Appropriate PPE must be worn.
Synthetic mineral fibres are used extensively for insulation in buildings. If these fibres are respirable and sufficiently biopersistent, they are also carcinogenic independent of their chemical identity or composition ("old mineral fibres"). However, since 2000 most commercial glass and stone wools in the EU are identified as low-risk because they disintegrate in the lung before they can cause harm. These are referred to as "new mineral fibres". Unfortunately in older structures and buildings a significant amount of biopersistent wool is still in place, and demolition workers need special precautions similar to work with asbestos; see for example the German Technical Rule for Hazardous Substances TRGS 521[17] Measures depend on the amount of fibres that can be expected based on a specific risk assessment. For more information see the OSH wiki article on Dusts and aerosols - man-made mineral fibres.
Hazardous chemicals contained in old drums, tanks and pipes
Depending on the use of the building a large variety of chemicals could have been stored at or in the building and remains could still be present e.g. fuels, solvents, acids, fertiliser. These have to be disposed of by specialised professionals. Cutting and dismantling tanks and pipes that contained combustible material need special procedures to avoid fire and explosions.
Hazardous chemicals being used for work
These may include cutting oils, cooling lubricants, hydraulic oils, de-rusting liquids, gases for cutting, explosives, expanding cement, solvents, etc. Any hazardous materials, should be clearly identified and where possible replaced by non-hazardous agents. Information about hazards and control measures can be obtained from the Safety Data Sheet (SDS). Workers should be instructed about the control measures for exposure and safe disposal.
Hazardous substances being generated during work processes
Dust development is one of the biggest problems at demolition sites. Water spraying systems should be used to contain the dust. Working with hand tools like drills and grinders may set free respirable crystalline silica (RCS) which can cause cancer. The tools should be fitted with exhaust systems. However, it might be necessary to wear appropriate respiratory protection, particularly at elevated heights. Fine dusts from flammable materials can burn or if airborne may explode. Removal of such dusts has to be done by wet mopping or by industrial vacuum cleaners.
fumes from gas cutting processes may need control measures such as local extraction systems.
Connected services
Essential services include the supply of gas, water, sewerage, telecommunications, electricity, chemicals, fuel and refrigerant in pipes or lines. Electrical power sources, whether overhead or underground, can be a major hazard. In addition to direct electric shock and possible electrocution, contact with overhead electric lines can lead to a variety of hazards including arcing, explosion or fire causing burns, unpredictable cable whiplash and the electrifying of other objects. All systems have to be located and disconnected. If this is not possible, pipes and cables must be labelled clearly and workers instructed accordingly.
Falls from height
During demolition and dismantling, workers can be injured falling from edges, through openings, fragile surfaces and partially demolished floors. The need to work at heights should be limited by performing work from ground level, e.g. by using high reach machines. If that is not possible the work should be carried out on solid construction that includes a safe means of access and egress. Fall prevention devices (e.g. temporary work platforms and guard railing), work positioning systems (for example, industrial rope access systems), or fall arrest systems such as catch platforms should be used.
Falling objects
Workers and passers-by can be injured by the premature and uncontrolled collapse of structures, by flying debris and tools. To control these risks any area where a falling object might reasonably be expected to land should be designated exclusion zones and hard-hat areas, clearly marked and with barriers or hoardings if necessary. Covered walkways need to be established. Machine cabs should be reinforced so that drivers are not injured.
Slips, trips and falls
Any debris and rubble should be removed as soon as possible to a safe place, and workplaces as well as pathways should be kept tidy.
Traffic on site
Effective traffic management systems are essential on site, to avoid workers being hit by vehicles in operation, turning, slewing, or reversing. Where possible, vision aids should be used and pedestrians and vehicles should be kept apart.
Hand tools and equipment
Workers doing manual demolition work have often to use heavy machines such as hammer drills, angle grinders, power saws, big hammers, jack hammers, demolition saws, hydraulic jacks, crow bars, concrete (rope)saws, and corers. Other machines and equipment which need extra care in handling include gas cutters, oxygen lances, personnel and/or materials hoists.
Managers and supervisors should ensure that machines and equipment are maintained properly and regularly, that they are operated only by competent workers, that appropriate guards and operator protective devices are fitted.
Big machines
The use of powered mobile plant such as cranes, excavators, bulldozers, and elevating work platforms requires strict traffic management arrangements to prevent collision with pedestrians or other mobile plant.
If cranes are used to suspend loads that are to be cut and then lowered to the ground, it is important for the loads to be accurately calculated. It may be necessary to cut samples in order to determine the weight per unit length or area. Where this occurs, the safe working load of the crane should be reduced by 50 per cent to allow for miscalculations in the test weighing. A similar approach should be followed where weights cannot be determined with reasonable consistency and accuracy.
Pulling down is sometimes done by removing floors and internal walls, attaching wire ropes to strong points on the upper parts of the building and using an excavator or other heavy machine to pull on the wire rope. There is a real hazard from flying wire ropes if they break due to overload or failure of the anchorage point on the building. This technique is not suitable for very tall buildings. Pushing over, again after pre-weakening, involves use of heavy plant such as crawler-mounted grabs or pushers. The cabs of such equipment should be shielded to prevent drivers from being injured by falling debris. The site should not be allowed to become so obstructed by fallen debris as to create instability for machine used to pull or push the building down.
The most common form of demolition is “balling" down, using a steel or concrete ball suspended from a hook on a crane with a jib. The jib is moved sideways and the ball swung against the wall to be demolished. The principal hazard is trapping the ball in the structure or debris, then trying to extricate it by raising the crane hook. This grossly overloads the crane, and either the crane cable or the jib may fail. It may be necessary for a worker to climb up to where the ball is wedged and free it. However, this should not be done if there is a risk of that part of the building collapsing on the worker. Another hazard associated with less skilled crane operators is balling too hard, so that unintended parts of the building are accidentally brought down.
Explosives
Demolition using explosives can be done safely, but it must be carefully planned and carried out only by experienced workers under competent supervision. The safe way to do it is, after pre-weakening, to use no more explosive than will safely bring down the structure so that debris can be safely removed and scrap salvaged. Contractors carrying out blasting should survey the structure, obtain drawings and as much information as possible on its method of construction and materials. Only with this information is it possible to determine whether blasting is appropriate in the first place, where charges should be placed, how much explosive should be used, what steps may be necessary to prevent ejection of debris and what sort of separation zones will be required around the site to protect workers and the public. If there are a number of explosive charges, electrical shotfiring with detonators will usually be more practical, but electrical systems can develop faults, and on simpler jobs the use of detonator cord may be more practical and safer. Aspects of blasting that require careful preliminary planning are what is to be done if there is either a misfire or if the structure does not fall as planned and is left hanging in a dangerous state of instability. If the job is close to housing, highways or industrial developments, the people in the area should be warned; local police are usually involved in clearing the area and halting pedestrian and vehicular traffic. Tall structures like television towers or cooling towers may be felled using explosives, providing they have been pre-weakened so that they fall safely.
Noise and vibration
Demolition workers are exposed to high noise levels because of noisy machinery and tools, falling debris or blasts from explosives. Frequent exposure to loud noise can permanently damage a person’s hearing. Noise can also create a safety risk if it makes it difficult for workers to communicate effectively or stops them hearing warning signals. Hearing protection will usually be required.
Vibrating hand tools used in demolition can cause hand-arm vibration syndrome (HAVS). Sitting on machines propelled by diesel engines can cause whole body vibration syndrome (WBVS). Workers exposure to vibration needs to be managed and reduced as far as possible.
Fire
Fire is a risk where hot work (using any tools that generate spark, flame or heat) is being done. During structural alteration, the fire plan must be kept up to date as the escape routes and fire points may alter. There must be an effective way to raise the alarm.
Excavating
Work in excavations deeper then 1 m needs especially careful planning and supervision. There is the risk of the ground collapsing along the side of the excavation. Before work starts, the ground should be surveyed by a person experienced in safe excavation work to establish the type and condition of the ground, especially the presence of water in order to determine a suitable method of support for the sides of the excavation.
There are special structures that would need special considerations, such as pre- and post-tensioned concrete, fire damaged buildings, basements, cellars, vaults, domes, independent chimneys, pylons, precast concrete panels, storage tanks and pipelines.
For workers conducting most of the activities mentioned in this chapter medical surveillance is required. Advice from an occupational physician is recommended.
The effectiveness of the prevention and control measures has to be checked regularly and improvements have to be implemented where necessary.
Outlook
With the aging of buildings and structures and with the aging of our society, demolition and reconstruction activity will continue to grow. As a result, a greater percentage of construction professionals will include these activities as services they provide. Demolition and dismantling are very risky activities. The existence of instable structures, hazardous materials, the need to use heavy machines, to work at elevated levels, and in unclear workplaces all demand improved safety and health planning and implementation. It is important that all stakeholders increase their efforts to protect the workers safety and health.
