Demolition Challenges at Ironbridge Power Station

Chapter 1 - Introduction

The Ironbridge Power Station cooling towers were an impressive 114 meters in height and although being set in a 350 hectare site, the site shared 2 substations that had to remain live throughout the works. Outside of the site, the access road was only one of two into the historic village commencing with its heritage museum was less that 1000m meters away, presenting a number of logistical challenges during the removal the 12,000 tonnes of asbestos containing material making up the internal packs, prior to the towers demolition, as well as the required road closures on the day of the blast. The surrounding gorge offered further constraints being home to the world heritage centre and susceptible to landslide, with the most recent of events causing the loss off a home in the days and weeks prior to their demolition, adding to the fear of locals. Structurally the 4 towers were built using 3 different construction designs and following constructional failure on other site, 2 were further subject to strengthening works and one rendered unsafe from falling materials. Finally, 2019 saw a number of other cooling towers demolished in the UK of which brought both success and failure to the eyes of the world.

Every engineering structure has a definite design life, which can range from 10 to even 100 years or more (Gehl, 2011). When this life span is surpassed, the structure may no longer be safe for human occupation however there are also a large number of structures that become the subject to end of life process due them failing to meet their economic demand or social requirement. This is when demolition or de-construction of the structure is carried out to free the space for other developments. Demolition can also be carried out to replace small structures with bigger ones. This is commonplace in towns and cities where low-rise structures are continuously replaced with high rise structures as a result of population surge. In other instances, a given building may experience some degree of structural damage, say due to a blast or fire or excessive loading, whilst in other cases, structural or engineering developments may give rise to concerns over the structures original construction design and therefore rendering it unsafe for its intended or ongoing use. Demolition ideally entails breaking down or removal of the components that tie the structure together (The demolition of structures, 2001). It is usually a systematic process given that other structures and human activities exist around the structure marked for demolition. When we consider the structures stability, its location and surroundings, the presence of hazardous materials even before applying the demolition methodology, we begin to understand some of the constraints that may be presented. For this reason, demolition needs to be approached in four distinct stages. This investigate research therefore looks into the constraints experienced, the decisions made and the lessons learnt from a number of cooling tower demolition events but first we look to differentiating between the four phases of demolition, applicable to the demolition of almost all structures. The first stage involves a thorough survey of the building (White and Kelly, 2006). First, the types of construction material used are identified - steel, timber, brick or concrete. Then, the date of construction and uses of the building since construction are identified. This helps identify the presence of any hazardous materials within and around the building and will form the basis for intrusive surveys to be carried out. Drainage conditions around the building are then assessed to predict whether demolition of the building is likely to cause erosion, flooding or water pollution. A major consideration in most projects is the local vicinity comprising of nearby schools, villages and residential housing and specifically how they will be affected by noise, dust, and vibrations, which are all common in any demolition process with limitations in their mitigation. Once a detailed assessment of the building is done, hazardous materials are the first to be removed from the building (Winkler, 2010). This is for the obvious reason that such materials can cause serious health effects as the demolition crew proceeds with its job. The most notable hazardous material in construction is asbestos. This has long been used in buildings mostly applied on steel beams and columns, and also concrete, asphalt, vinyl materials, roof shingles, pipes, siding, wall board, floor tiles, joint compounds and adhesives, due to its strength characteristics and fireproofing properties. When asbestos is damaged or crumbles, asbestos fibers get released into the air and this poses serious health problems to anyone in the vicinity.

The next stage is preparing a detailed demolition plan for the building and the individual structures that make up the building. Demolition and structural engineers go further than just the materials used, but also to examine the method of construction and load paths and connection points when they consider available methods of demolition. The distances between the structure under demolition and adjacent structures is accurately measured and engineering calculations computed to analyse the safety of the structures to be left intact (Strandholdt Bach, 2019). This methodology appraisal not only considers construction materials and methods but financial implications, programme allowances, safety, industry standards and proven practices. The outlined methods and measures are then followed during the actual demolition process. Although the process seems straightforward, demolition has been one of the most challenging activities in the construction industry (Higashi and Isobe, 2017). For small buildings and 2-3 story structures, the demolition process is not overly complicated since a combination of hydraulic attachments on common demolition spec excavators is sufficient to allow established, documented, remote, mechanical demolition techniques to be employed. The real problem comes in when large buildings have to be demolished. Hydraulic equipment may not be of much use since they all have a limited height they can reach. The use of other tools and techniques such as the implosion of a structure is then considered however; the infrequent use of explosives within mainstream demolition activities and lack of documentary case studies can present further concerns from clients, authorities and key stakeholders and as such result in additional constraints that they demolition contractor must consider and satisfy. In their journal titled Deconstruction, demolition and destruction, Thomsen, Scultmann and Kohler (2011) assert that governance has the most significant influence on demolition. Governance is herein defined as the regime made up of an intricate set of legal, financial, commercial and operational rules, drivers and barriers. Importantly, the demolition of a structure could reflect and consider best practice examples taken from projects such as the demolition of the 53-metre high brick chimney at Briggate, Leeds is reported to be one of the most complex demolition projects with communication and coordination taking place under extremely high pressures, capable of imposing mental health implications on most. During the demolition of the Cooling Towers at Didcot Power Station in 2019, debris projectile had struck a nearby powerline causing an explosion that injured innocent bystanders as well as an outage of power for more than 40,000 homes. Other notable demolitions that went wrong include the Pontiac Silverdome in Detroit of which failed to be successfully imploded in 2017 despite it being in a notoriously decrepit condition and the storage tower in Redbank, Australia is reported to have failed having remained in a leaning and structurally unsafe condition for more than 40 minutes before it finally collapsed. Present and future demolition undertakings should be well prepared to circumvent such technical constraints (Limer, 2017).

Chapter 2 - Requirements and analysis

The main aim of this research is to explore the technical, legal, planning and safety constraints experienced in a live demolition project in understanding their impact on the chosen demolition methodology and programme associated with a case study look at cooling tower demolition. To achieve this goal, the demolition project of the cooling towers at Ironbridge Power Station will be used as the predominant case study supported by a contrast, evaluation and comparative study of a number of other cooling tower demolition events. Therefore, the specific objectives of the research will include:

An in-depth literature review surrounding the demolition of cooling towers

An investigation and industry questionnaire diagnostic surrounding the technical challenges associated with the demolition of cooling towers.

An in-depth evaluation of the technical and legislative barriers associated with the demolition of cooling towers.

An in-depth evaluation of case studies associated with the demolition of cooling towers, including lessons learnt and best practices shared.

Conclusive evaluation of project lessons learnt, case study best practices and stakeholders considerations associated with the aims of this research and to allow the outcome of this project to be in demolition of future cooling towers.

Chapter 3 -Literature Review

The previous chapter introduced the research topic and outlined the goal of the current research, as well as the scope. In this second chapter ta detailed literature review has been carried out investigating the theory behind best practices in the demolition of cooling towers and review those best practices and lessons learnt. The aim is to explore the findings of other researchers regarding the research topic and use it as a platform or background for the current research however we must first consider those demolition methods available to a contractor before looking to define and explore project constraints.

3.1 Demolition Methods

Demolition methods are quite numerous and vary widely in their application, technology, efficiency, and costs.

Pitroda and Bhavsar (2015) categorised demolition methods into conventional and non-conventional. Conventional methods involve breaking down structures progressively either using hand tools or simple demolition excavators where non-conventional methods include explosives and high reach machinery. These conventional methods can also be referred to as selective or traditional demolition methods. They are mostly used when the building possesses some degree of structural integrity. These methods can also be considered progressive in their nature. Typically, such methods can also be used when only partial demolition is required. As of now, selective demolition methods remains nearly the only option regarding the refurbishment of buildings. The use of explosives or rope pulling by way of an example may not be practical because of their great destructive nature. Demolition methods can also be referred to as techniques and differentiate between hand demolition techniques, remote demolition techniques, use of rope pulling techniques and the use of conventional explosive techniques.

Use of the Rope Pull technique

Contrary to conventional explosives techniques, Able UK led the industry in 2012 when it employed the rope pull technique on six cooling towers at Thorpe Marsh Power Station. Although this method has been documented to have by hugely successful and beneficial, both financially and when considering the health, safety, environmental and ecological implications, the method has not been found to have been used by any other contractor since.

Use of explosives

It is not uncommon to have considered the use of explosives as an uncontrolled means of deconstruction as opposed to a required tool of engineers within the demolition industry. Despite being a recognised technique by the British Standards, the safe use of explosives and the controlled demolition of an oversized structure still remains a paradox to many. Naik (2018) gives the two major types of demolition initiated by explosives as Felling i.e falling like a tree and implosion i.e falling into its own footprint. The second type, also referred to as telescoping is considered to be more common where space is restricted, and vibration levels need to be reduced however more charges are likely to be used. Raadt (2000) defines three methods of demolishing cooling towers using explosives. The first being to overturn a structure, as defined by Naik (2018) as felling requires a cooling tower to initially be toppled. The toppling of the structure created by the removal of sufficient structural stability. The overturn then requires sufficient strength in the remaining ‘topple hinge’ or heel of the structure until enough kinetic energy is provided in order to overturn the structure. Raadt (2000) does however confirm that this method should not be applied to a cooling tower with a slenderness ratio of less than 4:1. Raadt (2000) defines a second collapse technique as a sideways collapse and although based on the same initial principles of toppling, it is achieved with a lesser topple and thus the structures collapse is not attained by a long way. In order for a reinforced concrete structure such as a cooling tower to be brought down using this technique, the rigidity derived from the reinforcement must be sufficiently reduced prior to or immediately after toppling. More interestingly, the substantial reduction in a cooling towers rigidity immediately after toppling is commonly seen by way of removing two thirds of a cooling towers shell using explosives milliseconds after the removal of the same two thirds of the towers legs. This method, referred to by Naik (2018) as implosion of structure is referred to by Raadt (2000) as a vertical collapse and dismissed as a method to be explored in the Netherlands as being the least reliable method as well as the most explosive-consumptive method of demolishing a cooling tower and was therefore not discussed further in the study, Despite the vertical collapse method being dismissed by Raadt (2000), in 1977 demolition of the first of the four cooling towers in Heerlen, in the Netherlands resulted in failure when the heel or topple hinge failed prematurely and the cooling tower effectively sat on its ring beam with its intended sideways collapse not being effectuated. The solution to this failure was to provide additional support to the remaining legs of the structures heel by way of underpinning the topple hinge, middle and end sections. Applying this design change to the remaining three cooling towers on the side resulted in their successful demolition with only 340 boreholes being drilled into each of their shells, loaded with approximately 20kg of AG-2, a medium strength explosive being divided equally between the shell holes. The chosen collapse design is therefore understood to be based on two predominant factors; slenderness and rigidity based on a ratio between the cooling towers height and base diameter.

Explosive Demolition Failure

Ramaswamy (2015) highlights the possibility of incomplete demolition and irrespective of the structure type, when using explosives as a methodology, demolition failure is always possible.

During the demolition of the Red Roads Flats in Glasgow in 2015, two of the eight multi-storey blocks remained partially intact, rendering the planned explosive demolition of the structures a failure. Reasons for the demolition failure were explored and had included

high strength of the tower or;

too little explosive.

The preparation for the implosion by DSR Demolition had taken place over a number of months and even with such detailed preparation, the vast experience of the contractor, and with all the knowledge on explosives, the possibility of the explosives malfunctioning remains. The author concludes that in the end, the structure does what it wants to do. Despite the extensive planning by the demolition contractor, the use of a structural engineer and those explosive engineers to carry out test blasts prior to the main event, failure can still happen with the demolition not taking the direction or form it was intended to. Foruzesh (2016) advises that after the building comes down, the explosives engineer should review the site and ensure all explosives were detonated. Due to the fallen debris stockpiles this can prove difficult and common practice is therefore for sufficient information and training by way of an on site toolbox talk be provided to the demolition machine operators of whom will be responsible for processing of the resulting debris material. The Civil Engineering (2011) journal expounds the risk of partial demolition when using the Athlone cooling towers as an example, the twin towers were earmarked for demolition following a structural failure in 2010 where top ring of one of the towers had failed. This structural failure rendered the tower unsafe and as both were constructed based on the same design and at the same time, both were subsequently fully demolished. The Athlone cooling towers were believed to be the world’s first explosive demolition of such strengthened cooling towers with 3000 boreholes being drilled into their shells, in addition to those used on the legs and learning of the impact the stiffening ring could have on the success of the implosion was key. If one of the two towers failed to fully collapse, it would have been unstable and would have left the cooling tower in a tilting position and at a dangerous angle. Although this risk will always remain on the demolition of any cooling towers, with the passage of time, and following the successful completion of other similar cooling towers, the risk of failure has almost all be diminished. In investigating the technical constraints associated with demolition works, it is imperative to also consider not only the demolition method employed but also those industry standards and then the legislative requirements that dictate the very nature of what we do.

3.2 The basis of Demolition Industry guidance in UK

In the UK, the demolition industry is guided predominantly by the British Standards 6187 for Demolition of which its latest edition was published in 2011. There are a number of supporting and relevant British Standards including but not limited to noise and vibration however these are applicable to all construction activities and we we look below at the demolition specific standards and industry guidance that we frequently rely upon. (Note that this is not intended to be an exhaustive list). Demolition industry guidance, over and above the British Standards are predominantly provided by the National Federation of Demolition Contractors (NFDC), the UK’s longest established and largest and network of accredited demolition contractors and as a result, frequently issues guidance to its members. Despite the Health and Safety Executive (HSE) repeatedly categorising demolition work as a construction activity and receiving fierce opposition from the industry, its guidance cannot be ignored. The 4 main guidance documents therefore considered to be predominantly applicable to the demolition of cooling towers are;

BS6187:2011 Code of practice for full and partial demolition

BS5607:2017 Code of practice for the safe use of explosives in the construction industry

NFDC – Exclusion zones in demolition

HSE guidance on Establishing exclusion zones when using explosives in demolition.

The provisions of each of these publications are discussed below.

BS6187:2011 Code of practice for full and partial demolition

This is a code of practice that addresses the demolition process, from early design stage upto and including the physical demolition process itself. It covers both partial and complete demolition of all scales, large and small alike as well as providing an overview of demolition methods available to the typical demolition contractor. It also gives recommendations on efficient management of the demolition process, how to ensure structural stability during demolition, providing examples of direction and intended collapse of structures, typical responsibilities in all stages of demolition, how to examine a given site for important information during the planning stage to ensure smooth demolition, advice on enforcing health and safety standards during demolition, risk evaluation and developing effective working plans, establishing and maintaining exclusion zones, and how to ensure the demolition activities remain environmentally friendly.

BS5607:2017 Code of practice for the safe use of explosives in the construction industry

This code of practice gives recommendations on how to handle, store, and use explosives during various construction activities. When using explosives as a demolition method thus to initiate a controlled collapse, the code of practice states that explosives can be used for both partial and full demolition concrete and masonry structures, steel structures, structures with a combination of concrete, steel and masonry, destruction of objects such as concrete foundations, beams, and columns, and detachment of erroneous structural elements. Explosives should typically be used to adequately weaken a structure so that it may collapse on its own. Explosives are therefore used to remove key structural elements of a building before structural stability is compromised and gravity prevails. Explosives can be fed into pre-drilled holes to allow the shattering of concrete or mounted on the surface of structures for cutting style demolitions used on steel structures, with or without the use of structural pre-weakening.

NFDC Guidance – Exclusion zones in demolition

These regulations by NFDC specify that demolitions of structures ought to be done in a way that prevents danger or reduce danger as much as possible if it cannot be wholly prevented. Additionally, all plans for demolishing buildings must be written down on paper before the demolition works commence. Although the NFDC does not produce any guidance on the use of explosives as a demolition method, the guidance document in relation to exclusion zones does refer to their use and as such, when designing and establishing an exclusion zone require all stakeholders to take the necessary steps to ensure no worker, passerby or spectator is injured as a result of an explosive event.

HSE guidance on Establishing exclusion zones when using explosives in demolition

This guide provides critical information regarding the establishment of exclusion zones during the demolition of structures generally and specifically when using explosives however, consistent with other guidance quantitative references are nor referenced. An exclusion zone is essentially an area of a given radius around a structure under demolition meant to shield people from flying projectiles as these are considered the primary impact where explosives are used. Secondary impact must also be considered when determining the size of the exclusion zone. In summary the determined extent of the exclusion zone should be of ample size to ensure that nobody outside of it is at any risk of harm.

It is required that at the time of the blast, nobody should be within the exclusion zone. Only where necessary, subject to a risk assessment and where blast protection can be provided can the explosives engineer or firing officer be permitted into the exclusion zone.

The exclusion zone is described as being made up of 4 critical areas;

the plan area of the structure under demolition

the area where a greater volume of the structure is intended to collapse

the area beyond the drop area where excess debris is predicted to fall

the buffer area between the predicted debris area and the peripheral of the exclusion zone.

The extent of the exclusion zone is dependent on factors such as the designed collapse mechanism, the type and strength of explosives used, the detonation sequence, the structural form of the building, contractors previous experience with explosives, the location of neighboring structures, the site topography, and the outcome of a risk assessment. Having looked initially at the guidance available to the demolition industry we are now able to briefly assess the applicable legislation.

3.3 Applicable UK Legislation

In the UK, demolition is identified as a construction activity and therefore requires adherence to an abundance of general construction legislation where these become relevant to a project or activity. The planning, organisation and control of any construction and therefore demolition project is the Construction (Design and Management) Regulations (CDM 2015) of which became enforceable on the 6th of April 2015 having superseded the 2007 version of the same. The regulation largely emphasizes on identifying the dutyholders (CDM 2015 parts 2 and 3) in any given project and their subsequent responsibilities during the planning and construction phases of the project. The regulations are understood to have been developed with the aim of reducing accident and ill health in the construction industry. This was done by identifying duty holders and assigning responsibility for any project both in its planning pre-construction phase, construction phase and post-construction handover. Up to now, little research has been done on the effectiveness of the CDM regulations specifically on the demolition industry. In 2004, the National Federation of Demolition Contractors lobbied for adequate coverage of demolition works withing the CDM regulations in an attempt to improve standards as little reference was made to demolition so far with the latest revision (2015) containing only one paragraph of specific guidance in part 4, section 20 of the regulation.

Other UK legislation applicable to demolition depending on the nature and extent of the works can include:

Control of Substances Hazardous to Health Regulations (COSHH) 2002

Health and Safety (Consultation with Employees) Regulations 1996

Health and Safety at Work, etc Act 1974

Lifting Operations and Lifting Equipment Regulations (LOLER) 1998

Management of Health and Safety at Work Regulations 1999

Provision and Use of Work Equipment Regulations (PUWER) 1998

Work at Height Regulations 2005.

All these are on a national scale and the list is non-exhaustive but a mere representation of the non-specific legislation that will apply itself to the industry on a generic basis. Pitroda and Bhavsar (2015) highlights the inadequacy of demolition standards. While construction regulations are several in any given county or country and are usually greatly detailed, the same is not true with standards concerning the demolition of buildings. As the project was located in Shropshire, West Midlands, the demolition of the cooling towers at Ironbridge power station must comply also with the regulations and requirements imposed by the Shropshire Council Building Control.

3.4 Defining and understanding project constraints

According to Young (2013), project constraints are any factor, be it material or immaterial, that impacts on the operations of the project team. To better understand these restricting factors, Chatfield (2015) proposed the project constraint model which features three major highly interdependent constraints, namely cost, time, and scope, at the 3 peaks of a triangle. If any of these restraints is altered in one way or the other, one of the other restraints must also be altered. While time and cost have been widely accepted by scholars, the scope has often been interchanged with terms such as goal, product, deliverable, and quality. Which such ambiguity, Brown (2009) added a fourth restraint to advance the triangle model into a diamond model, with the fourth restraint as quality. Further onwards, PMBOK (2009) advanced the model into a 6-point star that separated the input and output factors for the project from the factors dealing with the project process. As such, the first triangle had the original time, cost, and scope at the vertices, while the second triangle had risk, quality, and resources at the vertices. In construction, to which demolition is largely managed by, there are 8 major constraints, according to Lau and Kong, 2006. These are outlined below and where examples of these can be found to have impacted on the demolition of cooling towers, these have been identified.

Design constraints

Design constraints refer to issues that lessen the number of possible design solutions that can be used in a given project. Some of the most common design constraints include the equipment and technology owned or readily available to a firm as well as the original construction or design of the cooling tower. These design constraints have seen cooling towers demolished using traditional methods using demolition high reach excavators, rope pulling although more commonly being imploded using explosives. According to Foruzesh (2016), one of the main public concerns is the stability of the structure following the primary weakening and that it may collapse prematurely, at a time when no one around is prepared. As such demolition contractors are required to provide stability calculations with the aid of a structural engineer to prove such stability up until the point the collapse is purposely initiated. Failures have been recorded and include a 275ft tower at the Old Mad River Power Plant in Ohio which resulted in the cooling tower falling in the wrong direction in November 2011. The incident was reported to have been due to an undetected crack in the towers shell and caused spectators to run for their lives which property damage was recorded and power lines were taken out. The structural failure of cooling towers have been known in the UK with the most notable failure being recorded at Ferrybridge Power Station in November 1965 when 3 cooling towers collapsed during a period of high winds. Where precise calculations are sometimes required, demolition is further described as “50 per cent joining the dots and 50 percent creativity, because you’re dealing with a structure that’s full of unknowns”. (Sims, 2012).

Technical constraints

Technical constraints refer to factors that make it difficult to complete various demolition activities. These usually relate to how practical it is to use certain methods of demolition while at the same time conforming to applicable legislation and guidance. Technical constraints can include the demolition or subsequent construction sequence, the requirement to ensure sufficient space to safely carry out the demolition works as well as subsequent processing, ongoing accessibility of the site as works progress, availability of storage facilities as well as any demands or requirements imposed by the clients themselves. An example of this can be taken again from the ‘185-K3’ Cooling towers who reported to have presented 3 different implosion designs during the tendering stage and were further constrained by the cooling towers height which resulted in the contracts having to design a custom made crane lifted man basked to execute the drilling work and the subsequent placing of the explosive charges. The major technical constraints experienced with this type of demolition method include the risk of projectiles. With explosives, even the most trained specialists cannot guarantee that there will be no projectiles flying away from the building under demolition. As much as several control measures are put in place, projectiles flying from the building can travel to considerable lengths and wreak havoc on neighboring properties or passers-by. Of late, demolition companies have resorted to wrapping using geotextile membrane and chain-link to minimize debris and fly. (Ramaswamy (2015). After detailed consideration of all options and methods that could have been used for the demolition / deconstruction of the Calder Hall Cooling Towers in the UK, Williamson (2008) states that the ejection of high velocity small fragments was one of the top most hazards during the demolition. The cooling towers were located only 40 m from the UK's only nuclear Fuel Handling Plant and the Sellafield site has a number of other sensitive structures. Whilst implosion is the most common form of demolition for cooling towers, Thorpe Marsh Power Station in Doncaster was home to 6 103m tall cooling towers which were demolished using wire ropes in 2012, anchored and pull until the rope itself until the wire rope itself cut through the concrete until the tower lost all structural stability and ultimately the structure failed and collapse. This method, although successful and could be done without the need for explosives, required much more space than that of implosion and required more post demolition work by way of machine power the ‘finish the job’ from the ring beam and below. Contractors termed this the ‘pull down method’ and enabled each tower to be demolished less than 2 days post removal of all of its internal packing, hazardous or otherwise substantially reducing costs.

Economic constraints

Economic constraints refer to limiting factors in relation to the accessibility of funds throughout the project as well as the availability of plant and labour resources, collectively enabling successful completion of the project. In the event that the budget is insufficient, the construction project will likely be negatively impacted in terms of quality, safety, and efficiency. The absence of industry case studies is understood to have hindered demolition contractors in understanding the material arisings from the demolition of a cooling tower. The absence of information can impact the tendering process and even the project itself. This investigate study has however found that each cooling tower at Chapel Cross , standing at 90m produced 6400 tonnes of concrete and approximately 600 tonnes of rebar each whilst those at Ironbridge recorded 7500 tonnes for those original built towers each standing at 114m and 11500 for those towers strengthened in recent years in addition to 200 tonnes of rebar per tower for those original constructions with the strengthened towers producing more than double at 500 tonnes before finally recording some 4000 tonnes of asbestos cement pack and pipework per tower.

Management constraints

Management constraints refer to pre-existing site, client or local policies that restrict the tproject in some way and ultimately impact on time, cost or scope of the works. Such policies may include documentation review periods, thirds party authorisation, restricted working hours, overtime guidelines, the division or allocation of supervision, safety standards, workplace rules and an organisational working or operational culture.

Legal constraints

Legal constraints include those existing regulations and practiced legislation that the project must be compliant with to operate within UK law. These include health and safety regulations predominantly however environmental and waste permitting regulations, hazardous waste regulations, building act, employment law and local authority regulations are very much applicable. Non-compliance can have serious consequences for a business beyond any financial penalty imposed by the court and could include more far reaching consequences such as permit or license withdrawal and even the loss or cessation of the project contract itself. We consider legal constraints, over and above those existing safety requirements to those concerning the section 81 of the Building Act 1981 of which provides any contractor with permission to demolish and concerns itself with public safety. A huge concern for all issuing authorities and exasperated by the absence of documented industry case studies and the need to protect the public. With little knowledge of the impact of the proposed demolition works, exclusion zones sizes come into question as concerns for public safety increases. Foruzesh (2016) suggests that the radius of the exclusion zone should not be anything less than 2.5 times the height of the structure. Considering a 60 m tall structure, the radius of the exclusion zone should be 150 m upwards. Williamson (2008) states that during the demolition of the 88 m Calder Hall Towers, the exclusion zone was set to 200 m whilst the 114m towers at Ironbridge Power Station were demolished within a 350m exclusion zone. Foruzesh (2016) additionally suggests that a debris netting should be used around structures under demolition to trap dust and small pieces of demolition debris so as to safeguard the public and ease concerns. Applying this logic to the perimeter fencing of a normal demolition site is common however in more sensitive locations, screens are also used however when we consider large structures such as cooling towers being brought down in such instantaneous circumstances such as when using explosives, the erection of such netting is rather impractical. First, the scaffolding will be too high so as to cover the entire height of the structure. The scaffolding structure is likely to be free standing and as such unstable at such height presenting a greater risk that the dust itself. Any perimeter netting may need to be very large and prove ill-effective as in the case of water cannon sprays being used where height and rate of dust generation become difficult to manage. As such, many implosion demolitions will not make use of control measures. The demolition of the 138m cooling tower in South Carolina, America did however record very typically that the demolition of the cooling tower, where executed as an implosion, resulted in 1% of the cooling towers debris falling outside of the cooling towers own footprint. The client themselves recording that the falling of the cooling tower into its own footprint was indeed textbook and the resultant debris pile was not only well fractured by also neatly contained. Foruzesh (2016) also highlights the possibility of underground utility lines being damaged. It is a legal requirement to assess risks associated with live services and it is common, prior to demolition that services are isolated if not disconnected. This however is not always the case, certainly when we consider the location of cooling towers and as such designs for protection are likely to be considered.

Time constraints

Time constraints refer to the inevitable delays that mean key project deadlines will not be met. Whereas the contractor may be responsible for the delays at times due to insufficient planning, there are other instances when the delays cannot fairly be placed upon the contractor. Examples could include a clients request for additional work, delays associated with issuing local or legal permissions required, the absence of information, the discovery of hazardous materials or contaminated ground as well as any other unforeseen project event. The use of explosives is a highly effective demolition method in that it produces an instantaneous result, post planning and preparation and as such significantly saves on time and costs. It is a popular method for bringing down multi-storey buildings, especially those that pose critical hazards were they to be demolished by other methods. Pitroda and Bhavsar (2015) argue that implosion is capable of reducing the demolition period by nearly 80%. The remaining time being used during the preparation stage and subsequent post blast processing of the materials. The clients (Brady,2012) of the SRS ‘185-k3’ cooling tower demolition recorded in their post blast interview and evaluation that the use of explosives for such a structure and in order to initiate a collapse was not only safe but “on schedule, controlled and efficient”. He goes on further to conclude that they chose the method of implosion as it was considered the safest approach to reducing man hours at risk in demolishing the unique structure of a cooling tower. Contrary to this opinion, Able UK recorded the use of the pull down technique being used at Thorpe Marsh Power Station cooling towers as being almost entirely machine work thus reducing risk and man hours considerably with each tower shell being ready for demolition within 48 hours, depending on local weather conditions.

Environmental constraints

Environmental constraints comprise those environmental concerns that a demolition project must take into consideration to enable the successful completion of the project including air quality being the most visual however also surrounding land stability and pre-existing geo-technical considerations, weather, presence and type of wildlife, presence and nature of existing water courses, topography of the surrounding area. The use of explosives in order to initiate a structures collapse has for long been characterized by huge volumes of dust and other air-borne particles released into the air. If it happens that the building under demolition is in a densely built area, the surrounding residents may be put at risk of respiratory illnesses. Naik (2018) states that though asbestos may have been previously removed by licensed asbestos removal contractors, traces may still be present. As asbestos fears amongst the public gain momentum, reassurance is therefore required and can include the use of air monitoring at the boundary of the exclusion zone. The extent of local and surrounding development including its demographics can greatly impact on a projects permitted noise, air, water and waste tolerance or acceptability levels. The collapse of any structure is known to cause considerable amounts of ground vibration to a given radius around the building under demolition and the effect can be compared to that of a tremor or earthquake. Depending on the amount of explosives used and the size and weight of structure under demolition, the resulting vibration is frequently feared to be of a level that destroys the structural integrity of adjacent properties. Today’s standards of construction however are more likely to lend themselves to cosmetic cracks and the breaking of windows, particularly where they are single glazed or poorly mounted. Environmental damage is also of great concern however there is little evidence obtained during this investigation to suggest that any falling dust is harmful to either flora and fauna as it disperses although arguably it can appear to be unsightly. Despite best efforts, failure does happen and the demolition of the six cooling towers at Drakelow power station in July 2006 ended in disaster after the towers remained standing following a detonation failure. To the disappointment of many, the towers demolition was rescheduled to September of the same year, however disaster struck once again as three of the six towers had failed to collapse. An investigation quickly discovered that rabbits had chewed through the detonation card and some 50 mins later, the final three towers were brough to the ground. Dust and air quality are constraints applicable to most cooling tower demolition projects however little is documented of any measurable results. America was home to the successful demolition of the world’s second largest cooling tower ever demolished in 2010 known as the ‘185-3k’ cooling tower in South Carolina. Despite standing at 138m the contractors had however recorded that the 26,000 tonnes of concrete created a dust cloud that dissipated itself harmlessly within 12 minutes. As wind conditions on the day of any blast largely dictate the impact of any explosive event, Sims in 2012 puts forward the idea that the same amount of dust is generated whether a building is demolished by piecemeal or by more dramatically blowing it up however it is argued that at least during a pre-planned implosion, the inevitable dust is generated at a known time allowing for any necessary preparation. It can therefore be argued that the inevitable demolition dust will freely float into the air of the surroundings and the contractor should commit itself to a clear up operation, post the event. Able Demolition of whom successfully demolished the six cooling towers at Thorpe Marsh in 2012 reported that the use of their wire rope pull down technique had reduced the impact of ground vibration, dust and noise in comparison to the use of conventional explosive techniques of which are key environmental and ecological constraints on nearly all cooling tower demolition projects.

Social Constraints

Social constraints comprise issues likely to raise public concern over the proposed demolition activities and can lead to negative press, mass opposition and even project delays and abandonment. Social constraints are often borne from a lack of desire for change, certainly in a established or historic community where new development is frequently opposed to, or due to fear or uncertainty over the impact of the works on local community.

Chapter 4 - Methodology and Design

Whilst various research methodologies were considered including qualitative, quantitative and a mixed methodology xxx it was decided that the research investigation relating to the demolition of the Cooling Towers at Ironbridge Power Station would be better evaluated using a qualitative case study methodology. For the purpose of this research, the Ironbridge Power station will be predominantly used for the case study, supported a number of other smaller case studies identified during the literature review. This initial desktop study will include therefore an extensive literature review and case study evaluation. Detailed questionnaires will then follow and of which will be sent to a database collected of those participants of whom have opted into receiving information in respect of the blowdown events at Ironbridge and include local residents, local parish council members, local businesses and affected organizations. To complement the questionnaires, direct interviews will be carried out, especially on the main stakeholders of the demolition project. These include representatives from the principal contractor, the principal designer, the client, the local authority, representatives of the HSE, members of Institute of Explosive Engineers, those of the Institute of Demolition Engineers. (2 from each organisation or member body)

Justifying the use of the case study for the research

Yin, Merriam and Stake (2015) discusses the three main conditions that make it justifiable to use the case study as a research tool. The first instance is when the nature of the question is typically exploratory. That applies to investigation of constraints involved in demolition. It would be rather impractical to explore such constraints through laboratory experiments. The most reasonable approach is to use a real-life demolition project. Secondly, case studies are appropriate where the researcher is not able to control the site and participants. Demolition involves quite a number of stakeholders, from the government, the local authorities, the environmental authorities, health and safety authorities, the local dwellers around the area of demolition, the current occupants of the structure to be demolished, Heritage bodies, professional bodies and legal entities among others. There is no practical way in which the investigator can have control over all these participants, thus justifying the use of the case study. The third scenario is when the phenomenon under study is contemporary and the context is real life. ‘Demolition challenges’ is a real-life subject. One can’t explore the challenges unless the demolition is on course and constraints are being encountered. For these three reasons, the case study is an appropriate research tool for the investigation into the constraints faced during demolition exercises.

Research Strategy

Two basic methods will be used for collection of data for the current research.

Desktop Study

Detailed Questionnaires

Desktop study will be used for diagnostic investigation into the experiences, decisions and outcomes predominantly Ironbridge Power Station. In the researcher’s possession are documents such as the methodology appraisals for the demolition, guidelines from the Health and Safety Executive (HSE) regarding removal of asbestos, industry guidelines, regulatory legislation from local authorities regarding demolition of structures, and detailed technical designs of the power station. All such information is supported by the analysis of similar case studies and will include but not limited to the Calder Hall Cooling Towers Demolition. Secondary data is of huge importance and no research should be done without first searching for existing secondary resources related to the study. Secondary data helps the researcher to define the population in which the relevant persons can be identified of whom will later be subject to detailed questionnaire and interview. A detailed questionnaire will then be designed and issued to those persons identified. Questionnaires are a useful tool in investigating the expectations and perspectives of different people. In such demolition projects, each stakeholder or team member would have had expectations which would have had either been met or not. Every participant also encountered some constraint, which may be different from the other one. Questionnaires also allow the researcher to contact a larger population sample at a fairly low cost. They also enable the researcher to save on time since different respondents can fill the questionnaire simultaneously. They are also very effective when discussing sensitive topics which the participants may not feel comfortable sharing with the researcher. It may be to some a bit difficult to openly discuss the constraints faced for fear of victimisation. To complement the questionnaires, direct interviews were planned to be carried out, especially on the main stakeholders of the demolition project. These include the principal contractor, the principal designer, the client, the local authority, representatives of the HSE, members of Institute of Explosive Engineers, those of the Institute of Demolition Engineers. This will would give the researcher an in-depth understanding of the constraints faced during the demolition and the approach of the different stakeholders towards solving the challenges however as a coronavirus pandemic struck the world, the practicalities of this became difficult and as a result an additional questionnaire was drawn up for the key stakeholders.

Scope, restraints and limitations

This research should ideally involve all stakeholders in the demolition project as detailed above, representing those persons directly and indirectly involved in the demolition of the cooling towers of the Ironbridge Power Station. In addition, the local dwellers of the area around the power station will be asked to discuss their experiences during the demolition exercise. The major limitation of this research is the fact that it is taking place when the entire world is struck by the deadly coronavirus pandemic. The viral disease has resulted into partial and total cessation of operations for many businesses and departments. As it is not yet clear when the restrictions will be relaxed, there is a great likelihood of failing to reach some of the key stakeholders scheduled for interviews. Another limitation may be the fact that some stakeholders would restrain from openly discussing the constraints faced as it may be seen as a form of failure on their part.

Chapter 5 - Case Study Analysis

5.1 Ironbridge Power Station

Introduction

Ironbridge Power Station is located on the banks of River Severn in Shropshire, England. It was back in 1927 that the Electricity Authority of that time identified the area as suitable for power generation. The river waters would be used for cooling purposes while the connecting railway lines would be used for transportation of coal to the site. The presence of flat land across the area was also seen as very suitable for setting up the large turbine hall. The construction took place in 2 major phases. Ironbridge A came to completion in 1932. Electricity generation however began later in 1939 when all equipment was in place. The output then was about 200 MW. Further on, after the second world war, the Electricity Authority made the decision to set up Ironbridge B as a response to the increasing demand for electricity. The second station was set to produce 100 MW of electricity. The power station was designed by architect Alan Clark and landscape specialist Kenneth booth to perfectly blend into the environment. It came out as one of the most unique coal power stations in the UK. The cooling towers form the main attraction in the area with the structure being made from primarily red-pigmented concrete. These iconic structures saw schools and business taking on their name and shape into their names and logos. Later, the use of coal for power generation got into strong criticism by environmentalists because of the high degree of pollution associated with it. Despite the decision, made around 2012 to modify the station for use of biomass fuel, the power station had reached the end of its economic life and was subsequently sold to housing developers. The cooling towers were imposing and iconic for the small Shropshire village, a tourist attraction for many, appreciating the industrial revolution of the area and the uniqueness of their red pigmentation. Not necessarily visible to the eye, the four cooling towers were built using three different construction designs as well as additional structural support being added due to the structural failure and collapse of other cooling towers around the time of their construction. Having no use of the cooling towers, they were earmarked for demolition, amidst fierce protests by the locals who saw the structures as a great cultural heritage. The English Heritage did not find the concerns valid and amidst the cooling towers structural failing and concerns over the financial commitment from the local authority to maintain them in a safe condition, permission to demolish was granted and the towers were subsequently demolished in December 2019. The proposed demolition caused huge fears for the local authority, village and client as the gorge in which the power station and village was built on was susceptible to landslides. Furthermore, the power station was home to a substation and numerous powerlines, proving power to 5 counties and of which were unable to be turned off. This forms a great case study for exploring the legal, technical, planning, and safety constraints experienced in a live demolition project.

Planning

As part of the demolition of Ironbridge Power Station it was the intention to demolish the redundant cooling towers (Tower no 1-4) by the controlled use of explosives. The towers are of reinforced concrete construction, approximately 114m high, pond diameter 88m (approximate diameter at cut location 80m). Due to the collapse of Ferrybridge cooling towers redesign and strengthening works were carried out on the towers. This has led to three different leg and shell configurations. Planning commenced in July 2019 and it took some five months to achieve an execution date with meetings being held with Shoropshire and Telford Council of whom imposed 106 conditions in their section 81, unheard of in the industry from the members of the project management team and those key stakeholders. Nonetheless, the planning and co-ordination meetings dealt with each and every one of them and finally a date was set. During this planning stage, over a sixteen week period, averaging four weeks per tower, collectively 16,000 tonnes of asbetsos cement sheeting had been removed. This made up the packs in each tower, impossible to be removed manually they were arranged in a double layer banking system, were in poor condition and the structure, independent of the towers was considered to be unstable and therefore careful and progressive working was required. A large scale wet and drop method was carried out with daily perimeter reassurance monitoring being carried out and well as further personal monitoring bring carried out on the machine operators with no adverse readings being reported.

Demolition Methodology

Having analysed the structures and carrying out a comparative methodology and risk assessment with regard to the feasibility of the use of explosives to affect a mode of collapse against the risk to personnel from working at height during hand demolition or the possible risk to plant operatives and plant due to use of a high reach machine, demolition using the controlled use of explosives is considered the safest method to be adopted. Explosives are frequently used within the industry with their purpose to offer one of the safest way to remove key elements of a structure in order to initiate a gravitational collapse whilst at all times being able to maintain a safe exclusion zone. Using explosives in this way allows us employ a well-documented method of demolition referred to as telescoping. Described in more details below, this technique has been used by the team on other cooling towers with 100% success. Telescoping describes a near vertical collapse of a structure, caused by initiating enough compressive stress at the base to make the disintegration at the bottom a continuous process as the structure descends. This technique requires the explosives to cause sufficient movement to initiate the collapse, after which the gravity provides the main source of energy for the fragmentation. The design of these collapse mechanism has followed well-established principles employed on many previous successful demolitions of concrete cooling towers of this type. The collapse will be initiated by the explosive removal of 24 pairs of concrete legs (two thirds of their circumference) and 24 steel leg plinths on towers 1 and 2. Plus the formation of a slot by explosives two thirds the circumference of the towers in direction of fall made up of 2100 boreholes being pre-drilled and loaded with 52.5kg of explosive on towers one and two as these had historically been strengthened, 33.6kg of explosive on tower three and four, collectively requiring 172.2kg of explosives in their shells alone. When using any explosive material, the aim is to break the concrete only enough to cause structural failure and never cause excess or uncontrolled overblast. The explosive material (referred to as charge weight) can only accurately be established having completed one or more test blasts. The use of test blasts is a mandatory requirement of DSL for the use of explosives on reinforced concrete structures. Test blasts allow the explosive and structural engineer to ascertain the size, type and density of any reinforcing bar and concrete strength, type and condition

Overview of constraints

The demolition of the four cooling towers was an iconic event within the local area. The geographical location of the power station has caused a great deal on contention within the local community and with the local authority, namely due to its close proximity to Ironbridge village. Ironbridge village is a traditional tourist village, steeped in history for which the cooling towers are consider central to the working history. The village located approximately one mile away from the power station, along with its season accommodation and pre-existing traffic (access and parking) constraints led to a number of design considerations. Irrespective however of their location, there was without question only one way in which to demolish these 114m high concrete structures, and that was with the aid of explosives. The use of explosives themselves did not come into question during the consultation and design stage of this project but namely the secondary public protection concerns that arise from carrying out such works.

The design stage had concerned itself namely with the following:

The location of oil filled power cables, underground between cooling towers one and two

The close proximity of the WPD Electricity Pylon (65m in an elevated position behind cooling tower two and a second some 100m away from cooling tower one)

The generation of dust as a result of the proposed demolition works

The ground vibrations predicted and their impacts as a result of the demolition works

The air over pressure predictions and its impact as a result of the works

The traffic implications on Buildwas Road itself, the impact (if any) on the village and the need to create a safe viewing area in order to mitigate the impact.

Local and frequent land slides were also the cause for huge concern and a geo-technical engineer was tasked with understanding the impact the works would have on the surrounding geology.

Finally, the outcome was the devising of an exclusion zone of which would satisfy the concerns raised and ensure that any risk of impact (incident or harm) was to be eliminated outside of the designated exclusion zone.

Summary Outcome

The exclusion zone was put in place as planned and extended to 350m and requiring 46 sentries to maintain its exclusion. A further four persons were used in two motorised boats to ensure that the section of the river of which was captured in the exclusion zone, equally remained excluded from all personnel. Following the blast itself, initial success was evident by the falling of the towers almost instantaneously to the eye, reports soon came back from National Grid and Western Power to confirm that no impact or damage was caused to the underground oil filled cables that lay between cooling towers one and two, the closest electricity pylon which stood in its elevated position, no more than 65 meters away and the 400kv substation itself which shares the site at Ironbridge. Post blast, the geotechnical engineer carried out checks of the surrounding landscape for evidence of landslide or movement and an all clear was eventually received. No evidence of damage to trees were reported as sentries were required to inspect the area around them. Building surveys carried out post blast inspections on those residential properties from which the residents were evacuated and reported no damage had been caused. As not even a window was broken, the glazier on standby was able to be sent away. As promised during the planning stages, a road sweeper was mobilised, window cleaner put to works and the local scouts group opened a free car wash. Dust was inevitable however the demolition contractor was committed to doing all it could to minimise its impact. The blast was finally considered a huge success to the contractors, despite earlier concerns from the stakeholders with all 4 towers collapsing as intended and without damage. The collapse of the towers was considered a huge credit to the industry having, in recent times and even in the months prior, suffering from accidents and incidents being reported on similar projects.

Case studies

Given the current study involves an exploration of the technical constraints experienced during the demolition of the cooling towers at Ironbridge power station, it was imperative to consider in more detail other cooling towers that have previously been demolished and how the demolition works progressed. Four demolition projects were considered namely.

Calder Hall Nuclear Power Station

Didcot Power Station

Ferrybridge Power Station

Richborough Power Station.

5.2 Calder Hall Nuclear Power Station, Sellafield

Introduction

Calder Hall, located in Sellafield, was the world’s first commercial nuclear power station. It was commissioned by Queen Elizabeth in October 1953 and successfully generated electricity up to 2003. The power station was decommissioned after increasing concerns of the inadvertent collapse of the cooling towers due to aging.

Planning

The power station had 4 cooling towers in total, each rising to a height of 88 m. Each tower comprised 64 raking legs of 7.3 m height with a pond structure beneath the shell. A project team was put together to assess the best demolition method that would be both safe for humans and the environment and be cost-effective. The team settled on the use of explosives. The preliminary exclusion zone was set to 70 m for people and 110 m for any glassed structure. On the day of demolition, the exclusion zone was extended to 200 m, fully manned by 61 sentries.

Methodology

Surrounding utilities of significance were first identified. This was followed by the removal of all redundant plants. Other plants around the structure, such as the pump pits and water treatment plants, were demolished. All internals, including supporting columns, beams, 260 tons of timber framework, 6000 m3 of plastic packing, and 75 tons of asbestos pipes were then removed. Nearly 6,000 holes were drilled around the four cooling towers in a horizontal stitch pattern, as well as three 10 meter high vertical slots. After a successful test blast, explosives were loaded over a 10 day period and detonated. The two towers to the north were demolished simultaneously. After four minutes, the two towers to the south were demolished.

Overview of constraints

Some of the major constraints experienced in this project included i) protecting the nearby reaction towers from damage, ii) protecting the process waste line and interceptor sewer line next to the towers from debris damage, iii) protecting UK’s only nuclear Fuel Handling Plant which was only 40 meters away, iv) containing ground vibrations to protect other sensitive structures within the Sellafield site, and v) minimizing the amounts of radioactive waste released to the environment.

Summary Outcome

On the day of demolition, Saturday 29, 2007, each pair of the towers took about 4 seconds to fall to its footprint, as designed. Debris spread around the towers to a radius of 20 meters. On carrying out the post demolition checks, it was discovered that the windows of the reactors adjacent to the cooling towers had broken in the process.

5.3 Didcot Power Station

Introduction

Didcot power station, located in Sutton Courtenay, Oxfordshire used to generate electricity from coal and natural gas. It was rated the second most polluting establishment in Britain. It was closed in 2013 following heated protests by the public and environmental activists. The station had a total of 6 hyperbolic cooling towers. The first three were demolished in 2014 and the final three in 2019.

Planning

The first three towers, each rising to a height of 114 m, were set for demolition between 3 am and 5 am on Sunday, July 2014, but slight delays saw it demolished shortly after 5am. Devastatingly, during preparations for the demolition in 2016, a large volume of the boiler house collapsed as it was being weakened for explosive demolition by cutting into the structure. The incident killed 4 men, injured 5 men, and resulted in approximately 50 people being reported to have been exposed to high concentrations of dust. Following the clean up, investigation and resultant demolition works, the final three towers were demolished some years later at 7a.m. on 18th August 2019 however reached havoc once again as 40,000 people were reported to have lost power to their homes and three people suffered from minor injuries as demolition material had reported to have hit the overhead power lines.

Methodology

The detonation was carried out by demolition contractors Brown and Mason. The exclusion zone was set within the boundary fence of the power station. A small section of the nearby A4130 was closed for about 2 hours. The structures were washed down before demolition to reduce dust emission. Explosives charges were placed into pre-drilled holes throughout the circumference of the towers and upon initiation, the cooling towers successfully imploded, falling onto their own footprints.

Overview of constraints

One of the major constraints experienced during the demolition was the protection of the nearby pylons and transformer station from damage During the demolition of the towers in 2019, the transformer exploded and caused more upto 49,000 area residents to go without power until it was restored a short time later. Another constraint involved pressure from the public to shift the time of demolition to daytime hours to allow them to view the demolition, but the concerned authorities refused to give in to the pressure.

Summary Outcome

The demolition of the first 3 cooling towers was largely successful, without major accidents and pollution concerns. The major incident that had occurred with the boiler house causing the premature collapse of the boiler and ultimately the death of 4 men. The demolition of the final 3 cooling dowers was similarly subjected to the both accident and incident as the power line was hit by what was can be seen on video footage as the chainlink protection itself being released as a result of the charges being initiated, and quite simply, the ties used appeared to have failed at one side rendering the demolition event yet another failure for the former Didcot Power Station. Structurally the towers fell as indeed they were intended.

5.4 Ferrybridge Power Station

Introduction

The Ferrybridge power stations are a combination of three plants powered by coal on the River Aire in West Yorkshire, England, at the junctions of the A1 (M) and M62 roads. The first station operated from 1920 to 1976, the second station from 1950 - 19990, and the third station from 1960 to 2016.

Planning

The power station comprised a total of 8 cooling towers. The average height of the cooling towers was 114 m. The first one was demolished on 28 July 2019. Later on 13 October 2019, another four cooling towers were demolished. The remaining three cooling towers are still standing up to date.

Methodology

All the towers took about 10 seconds to collapse totally. On the demolition day, about 100 homes were evacuated to prevent any risk of injury arising from flying projectiles and undue vibrations. Roads were closed using rolling roadblocks. An exclusion zone was set to about 328 yards around the cooling towers.

Overview of constraints

The major constraint experienced during the demolition was the close proximity to major roads and residential homes. With such, the risk of injury was high if the demolitions went wrong. Containing dust was typically difficult and the exclusion zone was required to take consideration of this. The incidents having occurred at Didcot earlier in the year was industry news.

Summary Outcome

The controlled demolition of the cooling towers at Ferrybridge power station went on smoothly without major incidents and eventualities on 13th October 2019 when 4 of the towers were brought to ground level. The remaining cooling towers are set to be demolished by end of summer 2021.

5.5 Richborough Power Station

Introduction

The Richborough Power Station was located in northeast Kent, about 4 kilometers to the Southwest of Ramsgate and 3.5 km to the north of Sandwich. It was built next to the mouth of the River Stour and used to generate 336 MW of electricity. Having successfully operated from 1962 to 1996, the station was closed due to public pressure regarding the harmful environmental effects of the Orimulsion fuel used. The 3 cooling towers of the station were among the structures to be demolished. demolished on 11th March 2012.

Planning

The three cooling towers rose to a height of 97 meters. The demolition project was fiercely opposed by locals who termed the towers as a key part of the historical landscape given that they long acted as a landmark for boats navigating the River Stour. Preparation work for the demolition was carried out between May and June 2011.

Methodology

The three cooling towers were first stripped of all mechanical plant. The removal of asbestos by professional asbestos contractors followed. To demolish the towers, the contractor first got rid of the two slots in the shell through the use of explosives to make way for a rotational collapse in one direction. Other techniques such as basting, use of wrecking balls, and use of high reach excavators were ruled out citing unacceptable health and safety risk to the workers at the site, including noise, vibration, and dust. An exclusion zone of was set and was patrolled by the Police and contractor sentries.

Overview of constraints

Some of the constraints encountered in this demolition project included i) the need to pump out adjacent water ponds and discharge to the River Stour, ii) the need to divert traffic to the A2 and A299 roads as alternative routes to Ramsgate and Dover, iii) containment of the 17,000 tonnes of waste debris, iv) preservation of reptiles, birds, bats, water vole, otter, great crested newt, and peregrine falcon that are common to the area, v) prevention of contamination of the nearby water resources and soil, vi) suppressing dust.

Summary Outcome

The three cooling towers were finally successfully demolished on 11th March 2012. They were detonated in sequence with a three-second interval between the collapse of each of the structures.

Chapter 7 - Review of Findings

The findings of this research will be of great use to demolition contractors around the UK. Although it is expected that most of the contractors understand the challenges likely to be faced during demolition, not all of them have had first-hand experience in demolishing structures over 100 m tall using explosives and in such village locations. This case study will help them comprehend the nature of such demolition projects and be in a better position to handle such contracts if they are awarded in the future. The regulatory and local authorities will also find the research useful as they struggled to understand the true implications of the project as historical case studies were either not documented or not easily obtainable in a level of detail that provided reassurance, confidence or even guidance as to project specific requirements that should have been met in order to ensure that the resultant demolition event was free of accident and incident.

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