The spectacular sight of an industrial chimney demolition is something to behold, often attracting millions of views on YouTube. However, these impressive events demand the application of highly specialist technical knowledge and safety expertise to protect workers, members of the public and surrounding structures and facilities. The minimisation of noise, dust and potential site run-off (especially any residue materials with the potential for environmental harm) is a further factor in the delivery of a successful chimney demolition.
Where space permits, arguably the simplest way to demolish an industrial chimney is by ‘felling’ – either via cutting or imploding using carefully placed, sized and timed explosives. Of course, in reality, there is almost always nearby infrastructure that requires protection, such as property, roads, rail tracks, utilities or waterways. These often require safeguarding not just from falling debris, but from vibrations too.
DEMOLITION
Where demolition using controlled explosives is feasible, the top priority is safety. Indeed, the Health and Safety Executive (HSE) specifies that principal contractors are responsible for planning, managing, monitoring and co-ordinating health and safety issues during demolition work, while site managers must ensure the supervision of workers and that they follow safe working practices.
“Site preparation for demolition is detailed and thorough, regardless of the proposed method,” explains Nikki Wallace, business development manager at the demolition contractor Hughes and Salvidge. “Activities include removing internal structures, drilling holes for the placement of explosives – and wrapping columns with fabric and fencing before firing the explosives.”
Although using explosives as a method to demolish indicates that the building or structure will be ‘blown up’, this is not actually the case. “Controlled demolition employs a serious of small explosions, strategically placed within a structure, progressively detonated to encourage a collapse by weakening or removing critical supports,” continues Wallace. “Explosives on the lower floors then initiate a controlled collapse and the chimney fails under its own weight, succumbing to gravity.”
Controlled demolition is applicable to virtually any type of structure but is commonly used on buildings of particular height, such as industrial chimneys and cooling towers. “The use of explosives in a controlled demolition is essentially the quickest, safest and most economically viable method of bringing down such a building,” states Wallace. “However, the use of this method all depends on the surrounding area – whether other buildings are in close proximity and if tenants and/or residents occupy those buildings. We must also take the local environment and wildlife into consideration.”
Hughes and Salvidge carries out all demolitions to BS6187:2011 and its work complies with applicable legislation, Guidance Notes, Acts, British Standards and Approved Codes of Practice that include the Construction Design and Management (CDM) regulations and the National Federation of Demolition Contractors (NFDC) regulations. The company also operates an integrated management system that addresses all areas pertaining to health, safety, quality and the environment. The system is subject to audits by a UKAS-approved organisation.
NERVES OF STEEL
Another demolition contractor with extensive experience in this area is S Evans & Sons, which recently completed the successful explosive demolition of the former batteries chimney at DLCO (Dawes Lane Coke Ovens), British Steel, Scunthorpe. As part of an upper tier COMAH (Control of Major Accident Hazards) site, the project also included the demolition of the preheat tower, former ovens, cooling towers and various associated bi-product processing facilities. As the site remained live throughout the demolition, special consideration was required at planning stages to phase the demolition and avoid impacting production. S Evans & Sons therefore co-ordinated the works around a methodical decommissioning strategy.
The first phase of the works included the demolition of the redundant preheat tower, a steel-framed 65m-high structure. Removal of the tower took place using two explosive demolitions. A design and cutting sequence developed and executed by highly trained and experienced personnel prepared and pre-weakened the structure to ready it for explosives.
On each day of the blowdowns, it was necessary to evacuate British Steel staff and neighbouring businesses to a 500m radius, requiring the movement of more than 200 people and the assistance of the local police and Humberside Fire and Rescue, as well as liaison with Network Rail due to the proximity of its infrastructure.
The remainder of the demolition at Dawes Lane used cut and lift and mechanical demolition techniques to remove further structures, including two chimney stacks.
DISMANTLE WITH CARE
There are many ways to dismantle – rather than implode – brick and reinforced concrete industrial chimneys. The most basic of these is manual disassembly. Here, it is necessary to give special attention to the competent organisation and safety of workers, who will start disassembly operations at the top of the chimney. They will typically use rope access and specialist rigging techniques, working with equipment such as sledgehammers, perforators and jackhammers to disassemble the chimney into fragments.
Sometimes it is possible to contain debris within the chimney structure itself using scrupulous planning and protective strategies. Contractors can work at a pace that maintains process efficiency while minimising vibration and dust to ensure surrounding areas remain relatively free of fugitive airborne contaminants.
For shorter chimneys and towers it may be possible to use an excavator mounted with hydraulic shears. Alternatively, hybrid manual/machine approaches include the use of diamond wire and demolition machines supported by mast climbers. This approach is popular for large diameter chimneys or stacks with thick walls.
COOL UNDER PRESSURE
In 2021, demolition and decommissioning company DSM demolished eight, 11,000 tonne, 80m-high redundant cooling towers at Eggborough power station in North Yorkshire on behalf of its real estate regeneration client, St Francis Group. DSM’s approach was to demolish the cooling towers in two lots of four by means of high-velocity explosives. The company appointed a pre-selected bona fide explosives engineer to design the complete mechanism. In close consultation with the local authority, HSE, the Police and statutory undertakers, DSM successfully delivered the works without accident or incident.
To achieve this outcome there were a number of project constraints and challenges to overcome. For instance, it was necessary to create a 350m diameter exclusion zone around each of the two blast events, in effect establishing a ‘sterile’ working area. DSM also organised major road closures around the exclusion zone involving guarding by company sentries and North Yorkshire Police. Another requirement was making contact with all potentially impacted third parties in and around the exclusion zone. Here, the works demanded detailed planning between Northern Gas Networks, National Grid (main sub-station only 65m from the demolition) and nearby business Saint-Gobain Glass to ensure measures were in place to protect their live assets.
Extensive cleaning of adjacent roads was also required post-demolition, although the exclusion zone and road closures reopened 90 minutes afterwards. DSM reports it received no complaints from any third-party stakeholders during either blast event.
In July 2022, the DSM saw its last two remaining structures at Eggborough Power Station demolished in a controlled process with the use of high-speed explosives. The 50,000-tonne steel-framed boiler house and 20,000 tonne 200m-tall reinforced concrete chimney succumbed over a 10 second period.