Prepping for power plant demolitions

Many risks are associated with the demolition of power generation plants, such as premature collapse, falling debris or unexpected environmental release while demolishing various types of structures.

To avoid such events, significant planning is required before commencing a power plant demolition project, and crews must understand the requirements of the job and any potential hazards. With this information, the appropriate demolition methodology can be selected.

While a detailed understanding of the infrastructure and associated risks will help to plan for safe demolition work, demolition stakeholders need to recognize the potential for unforeseen conditions and the need for procedures and processes to communicate and manage changes identified during demolition.

Assessing the job

Before starting demolition operations, the U.S. Occupational Health and Safety Administration (OSHA) requires that an engineering survey of the structure be conducted by a “competent person,” defined as “one who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous or dangerous to employees and who has the authorization to take prompt corrective measures to eliminate them.”

According to OSHA, the purpose of this survey is to determine the condition of the framing, floors and walls and the possibility of unplanned collapse of any portion of the structure being demolished.

Given the nature of demolition activities, site conditions constantly are changing. This could necessitate frequent reevaluations of site conditions by competent persons, including support from professional engineers.

For completeness and contractual protection, adjacent buildings or infrastructure that could be impacted by the demolition also should be included in the survey.

Some of the general requirements to be addressed in the engineering survey include:

• reviewing existing architectural, structural and as-built drawings for completeness and accuracy and/or developing as-built sketches as deemed necessary;
• identifying building materials, substances and wastes that will be generated by the demolition and associated proper handling techniques;
• identifying personnel with sufficient plant knowledge, such as the maintenance manager and/or environmental manager of the facility, who can provide relevant information regarding the plant operation and history that may impact methodology;
• identifying confined spaces, exposed edges, voids or underground tanks and structures;
• identifying hazardous chemicals, gases, explosives, flammable materials or similar dangerous substances that may have been used or stored on the site;
• addressing instances where historical events could have damaged and weakened the structure (for instance, past boiler explosions); and
• identifying the presence of ongoing underground services that may impact equipment selection or protection requirements for the project.

Laser scanning and BIM models

In addition to reviewing existing as-built drawings, other tools are available to evaluate the structure and prepare design drawings for demolition. Several methods can be applied to create structural drawings, including working with an engineering firm to prepare drawings, three-dimensional laser scans or imaging of the structure to develop a geometric model.

The laser scanning or imaging can be done from multiple fixed points on and around the structure or using drone technology, depending on the structure accessibility. A 3D laser scan of the structures can provide an accurate representation of the facilities, which can be used to help manage the planning process and reduce the risk involved with the project.

Completing a 3D laser scan could be appropriate where the existing drawing set is inaccurate, incomplete or difficult to read. Undocumented changes also could have been made to the structures during the operational life of the facility being demolished.

Having a complete 3D model of the facility results in a more accurate representation of the structure for planning, analysis, visualization and stakeholder engagement. These types of scans are particularly relevant for more complex structures such as boiler houses.

Having a complete building information model (BIM) dataset allows for:

• quantity take-offs and volume assessments for waste and recyclables, etc.;
• dimensions and geometric properties, which, in turn, provide better information for the selection of equipment and planning of work areas;
• improved accuracy on the building’s structural analysis and assessment;
• a better understanding of the facility and, therefore, reduced unknown conditions or modifications; and
• information to assist with comparing actual structural behavior to calculated behavior.

A BIM survey does not replace the need for site inspections, condition assessments or other preplanning activities. While the BIM can provide information regarding member sizes, it does not provide information on corroded or overstressed members. To ensure a usable dataset, stakeholders should collect a high density of data points to create a point cloud dataset with sufficient information to help identify the structural member sizes.

Additionally, it’s important to define the time that the modeling company will need to convert the point cloud data to a complete 3D model and include that in scheduling.

Addressing hazardous substances

Throughout the operation of the power plant, chemicals could have been used as part of the process and might have been in contact with building materials. Regulated building material inspections are performed to understand any substances that could be present in the power plant from when it was in operation.

Inspections can be done by reviewing all safety data sheets to understand the chemicals used and stored on-site. Inspections, inventories and sampling typically will include asbestos, silica, lead, fluids, residues, lighting, radiation sources, batteries and wastes in addition to any specific regulated materials identified by the owner.

The inspections also should consider operational processes, maintenance practices and any historical events such as fires that could have used chemicals in the management of the event.

It also should be determined if any type of hazardous chemicals, gases, explosives, flammable materials or similarly dangerous substances have been used in any pipes, tanks or other equipment on the property. When the presence of any such substances is apparent or suspected, testing and purging shall be performed and the hazard eliminated before demolition is started, according to OSHA.

Examples of hazardous materials that can be found in power plants are polyfluoroalkyl substances and perfluorooctanoic acid, polychlorinated biphenyl (PCB), oils and solvents, and chemical residues that might have come in contact with building materials.

Environmental inspections and sampling

Environmental inspections should be completed and abatement and materials management plans prepared to address worker exposure, define handling and disposal of regulated materials, specify actions that will be implemented for spill prevention and control and confirm that evaluations performed incorporate the duties of building and facility owners to determine where these materials may be present.

An investigation of asbestos-containing materials by a registered asbestos consultant is required to produce an asbestos register and management plan suitable for demolition. This plan will provide guidance on industrial hygiene requirements, handling and disposal.

Exposure to chemicals and materials, including inhalation, ingestion, skin absorption or contact with dust or any material or substance at a concentration above those specified by OSHA, should be avoided.

If hazardous or toxic materials such as lead or cadmium are identified, specific standards must be followed. Refer to Standard No. 29 CFR 1926.62 for lead and 29 CFR 1926.1127 for cadmium for those requirements.

OSHA also provides a publication for lead in construction that provides a useful overview of lead standards-related topics.

Complex chimneys and stacks

Chimneys, or stacks, and the internal flues, or liners, have unique considerations that could impact their demolition. These conditions include construction materials, geometry and third-party installations.

Concerning construction materials, additional considerations should include the properties of the stack and liner material, and documents reviewed should include design drawings and historical stack inspections.

Specifically, the review of historical documents minimally should consider steel and concrete properties as well as the annulus space and connectivity between inner flues and outer reinforced concrete wind screens; the location of support for liners or flues and connection to the foundations or the outer stack; and exterior cracks or spalling for the stack or masonry liner.

Masonry liner material also should be assessed for contact with process chemicals, regulated building materials and residues.

The presence of breach openings, windows or doors in both the stack and the liner should be documented and compared with original drawings to identify any changes that have been introduced after initial construction was completed.

This information will be essential for cases where 3D structural modeling is necessary. Stacks frequently have navigation lighting and markings on them that might have to be maintained until the structure is demolished; therefore, consultation with Federal Aviation Administration and Federal Communications Commission authorities could be required depending on the size and location of the stacks.

This article is an excerpt from the National Demolition Association’s white paper titled “Considerations for Demolition of Power Plants,” published in September 2023. To view the full document, visit chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.demolitionassociation.com/Portals/0/Considerations%20for%20Demolition%20of%20Power%20Plants%209-24-23_FINAL.pdf.