Intumescents in focus

With the use of intumescent coatings growing year on year, James McGilligan provides an overview of this vital tool from the passive fire protection toolbox.

As architects and designers relentlessly explore the boundaries of building design, they propel the demands of the supporting elements of the building to reach new heights of excellence. Open plan layouts, extensive use of glass façades, and the integration of green spaces are redefining spatial dynamics and promoting a sense of connectivity with the surroundings. However, this modern architecture often necessitates innovative load-bearing structures, and with its exceptional strength-to-weight ratio and quick erection times within a fast-paced environment, steel is a popular material within the structural frame of any building. However, steel does not inherit a resistance to fire like other materials and requires structural fire protection in order to comply with the Building Regulations.

The call for intumescent coatings has grown significantly over recent years, from having a 20% market share of fire protection systems in 1992 to having almost 80% of the market share in 2012. Intumescent coatings are designed to protect steel from the damaging effects of heat and fire. When exposed to elevated temperatures, intumescent coatings undergo controlled charring and expansion and this charred layer serves as an effective insulating barrier, therefore slowing the heat transfer to the substrate.

So, what makes intumescent coatings a popular choice when it comes to structural fire protection?

  • Aesthetics – Intumescent coatings can be formulated to have a smooth and aesthetically pleasing finish. With the developments in architecture, it is becoming more popular for the structure of a building to be exposed, which is relatively easier with intumescent coating protection.
  • Versatility – Intumescent coatings are a versatile product, which can be adapted to suit a diverse range of projects.
  • Application – Intumescent coatings are easy to apply both on-site and off-site and can be applied using conventional methods such as spraying, brushing, or rolling. With quick application times, intumescent coatings can be applied to suit any project programme.

However, intumescent coatings can only be effective under fire conditions when appropriately specified, applied, and maintained correctly.

Specifying intumescent coatings

It is normal for building designers to see structural steel within their design and state “Intumescent Coatings to achieve 60 minutes fire resistance”, however, this is not always the most practicable method when reviewing the design on site. Intumescent coatings need expansion room in order to be effective; this expansion zone is usually fifty times the dry film thickness, or 50mm. Therefore, if the structure of the building is protected with intumescent coatings, the structure needs 50mm adjacent clear space. This is not always the case on site, with designers trying to maximise space, sometimes the services within the building run tight to the steel or walls are built up tight to the structural steel and doing so sacrifices the effectiveness of the intumescent coatings.

Other scenarios include when the structural steel runs in line with a compartment wall. In this case, intumescent coatings are not the correct fire protection method, as Approved Document B states that compartment walls are to achieve Stability, Integrity, and Insulation ratings (REI). Intumescent coatings do not achieve the insulation rating, and therefore when steel is in the line of a compartment wall, an alternative method to structural fire protection is required.

It is imperative for fire consultants and building designers to conduct a comprehensive review of service support methods. In certain instances, services are reliant on structural steel elements protected by intumescent coatings. It is important that these connections are handled with due diligence, aligning closely with the guidance provided by intumescent coatings manufacturers.

Applying intumescent coatings

Applying intumescent coatings involves a meticulously orchestrated process that encompasses substrate preparation, consideration of environmental conditions, minimum dry film thickness (DFT), thorough measurements and recording, and adherence to the Golden Thread principle.

  • Substrate preparation: Prior to applying intumescent coatings, the substrate surface must be clean, dry, and free from contaminants, such as rust, grease, or loose debris. Poorly prepared surfaces results in the intumescent coatings failing to be effective during fire conditions. If the substrate surface is not properly prepared, the adhesion of the intumescent coating will be adversely affected, resulting in the intumescent coating peeling off post application.

  • Environmental conditions: When applying intumescent coatings, it is imperative that the required environmental conditions specified by the product manufacturer are adhered to. Deviations from the temperature, humidity, and ventilation parameters can lead to the intumescent coatings failing under fire conditions, or even falling off the structural steel post application. It is crucial to constantly monitor the environmental conditions during application, with comprehensive records kept and provided to the client upon completion.

  • Compatibility: If a topcoat is required due to environmental conditions or architectural reasons, it is imperative that the applied topcoat is compatible with the intumescent coatings. If the incorrect topcoat is applied, this may have an adverse effect on the performance of the intumescent coatings. It is vital that the correct system is installed by third-party accredited contractors.

  • Dry film thickness and recording: Accurate dry film thickness is crucial to achieving the intended fire protection. The DFT is specified by the manufacturer and varies depending on the required fire rating and steel sizes. To ensure consistency and uniformity, specialised thickness gauges are used to verify the coating’s thickness throughout the application process. The dry film thickness requirements should comply with the guidelines provided in Section 4.7.3 of ASFP Technical Guidance Document 11, with at least 10% of the steel members surveyed as per Section 4.7.4 of the same document. Comprehensive records should be kept of the dry film thickness measurements, including coating thickness, date, time, location, and steel size. This documentation not only serves as a quality control measure but also provides a traceable record ensuring compliance with the Golden Thread.

The Golden Thread principle is a fundamental concept in fire safety that entails maintaining a clear and unbroken line of information and responsibility from the design and specification stage, through to construction, maintenance, and eventual decommissioning. In the context of intumescent coatings, this means that the specified fire protection requirements, including dry film thickness and application procedures, must be seamlessly communicated and consistently executed at every stage of a building’s life cycle. This ensures that the intended fire safety measures remain effective throughout the structure’s existence.

Maintenance and repair

When intumescent coatings are applied in accordance with the manufacturers’ guidelines, it is generally accepted that it will provide the required fire protection for the lifespan of the building. However, inspections and product maintenance are still important, as damage to the coatings can occur through other forms of building maintenance. 

Regular inspection should be carried out by the building’s responsible person, and should be carried out in line with the product manufacturer’s specification. There are other factors that can also impact the inspection schedule that should be considered:

  • Products used and manufacturer recommendations

  • Location of the protected steel work (i.e. above a ceiling)

  • Type and use of the building (i.e. a car park, warehouse, or commercial office building)

  • Environmental considerations (i.e. a highly corrosive environment such as high humidity and temperatures in swimming pools).

Where there appears to be damage to the intumescent coating, a professional coatings inspector should be employed to inspect the severity of the damage, and recommend any remedial work required. The remedial process of intumescent coatings is a timely and complex process which should be completed by accredited contractors only. The process involves stripping the existing coatings, applying new primer, intumescent coatings, and topcoat. Carrying this out in an existing live building comes with great challenges and an expert should be consulted.

Advances and accreditation

With the increased scrutiny on the effectiveness of fire protection strategies and the performance of the products used within the construction of buildings, building owners are now more than ever being urged to act and put the safety of building occupants first.

Some product manufacturers have heavily invested in product identification tools and processes to be able to guarantee traceability of their products. This technology means the product manufacturers are able to identify that the products installed on site meet the requirements of the building specification, reducing risk for both building owners and building occupants.

Product manufacturers have additionally invested in new coating systems that can be applied in adverse weather conditions. This advancement means that the intumescent coatings can be applied in colder temperatures, and whilst these products ensure that project programmes can continue and deadlines can be met, they do come with a financial cost implication.

Third-party accreditation serves as a catalyst for encouraging best practices in the installation and upkeep of passive fire protection products. It demands the implementation of rigorous quality assurance procedures embracing competence, documentation, and processes. This ensures that certified companies meticulously execute and document their quality control measures, affirming the appropriateness and reliability of their fire protection systems.

When tendering for the application of intumescent coatings, it is advised that a third-party accredited company is employed, in order to ensure reliability, accountability, and traceability of the application.

For a successful specification and application of intumescent coatings, the following steps should be considered:

  • Familiarise yourself with the fire resistance rating and Building Regulations requirements applicable to the specific project.

  • Consult with the project design team to ensure they specify and approve the correct intumescent coating to meet the requirements of their design.

  • Ensure the correct application method is adhered to (i.e. number of coats, substrate coating, topcoats, and drying times).

  • Ensure the environmental conditions are as per the manufacturer requirements.

  • Implement a stringent quality control process during application to ensure the correct coverage. Regularly inspect for any defects, irregularities, or areas of insufficient coating thickness, especially on a live construction site.

  • Check whether any subsequent finish will affect the performance of the intumescent coatings (i.e. ensure a compatible topcoat is applied when required).

  • Maintain thorough records of the coating specifications, application methods, test results, DFT, and environmental conditions.

  • Employ a maintenance programme to inspect and maintain the intumescent coatings during the life cycle of the building.

For further information, visit Crossfire Specialist Contracts.

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James McGilligan is an Engineer at Crossfire Specialist Contracts.