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Clad or Coat? Strategies for structural steel fire protection

Coral Morgan, Product Manager – Fire Protection at ROCKWOOL UK, discusses how non-combustible insulation can help to balance design demands and deliver a seamless structural steel fire protection strategy.

When designing structural steel buildings, consideration must be given to performance in the event of a fire. Ensuring a building meets the requirements of Approved Document B (ADB), passive fire protection is integral when safeguarding structural stability and safely protecting occupants and firefighting teams. That said, in modern building standards, acoustic and thermal performance are also increasingly coming to the fore. With these criteria often considered later in the build programme there are common challenges faced which impact project timescales and costs. Coral Morgan, Product Manager – Fire Protection at ROCKWOOL UK, discusses how non-combustible insulation can help to balance design demands and deliver a seamless structural steel fire protection strategy.

Structural steel buildings have long been used in architectural design based on their ability to support the creation of lighter, more versatile spaces that facilitate efficient and effective construction programmes.

As the urban landscape becomes more densely populated with homes and commercial buildings, the need for flexible and secure premises is fundamental.

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ADB emphasises that when designing buildings with a structural steel core, structural elements should be capable of withstanding the effects of a fire for appropriate periods of time, without loss of stability.

The requirements of ADB differ depending on varying building factors such as its size, height, use and occupancy, but ultimately the building is required to maintain its resilience for a reasonable period.

Whilst this is essential when approaching construction, navigating additional building performance factors at design stage can contribute to overall performance, whilst reducing delays to site programmes.

Addressing additional requirements

In areas of increased urbanisation, the acoustic performance of a building is becoming a major factor. Reducing the transfer of noise and vibrations through steelwork to create more comfortable internal spaces is a requirement architects are needing to negotiate on a larger scale.

Additionally, as net zero and carbon reduction are high on the construction agenda thermal performance is not only integral to meeting Approved Document L (ADL), it is also a key consideration for increasing energy efficiency.

“Ensuring that fire protection is specified at the design stage can minimise the requirement for non-standard applications and can lower the risk to buildings.”

With passive fire protection measures not generally considered in the initial stages of design and specification, additional implications such as lack of space, acoustic impacts and thermal bridging can be encountered further into the build programme.

This poses challenges within the overall process as contractors may be required to revisit already completed work to satisfy further requirements – causing site delays and impacting on project cost. Situations such as these can be mitigated by balancing all design, compliance and performance standards from the early design phase.

Insulating performance

Thermal and acoustic demands are becoming increasingly complex factors within structural steel building design. However, common fire protection strategies do not always support the seamless application or navigation of acoustic and thermal criteria.

For example, intumescent coatings are typically specified for fire protection in structural steel buildings. Applied directly to the structural beams, when exposed to fire this triggers a chemical reaction which provides insulating protection to the beam to maintain structural integrity. Although effective for protecting the steel under ADB by supporting it to maintain stability, the coating process does not provide any acoustic or thermal insulation.

Another consideration is in areas of the building where steel beams interrupt or connect to thermally performing constructions as thermal bridging can occur – reducing the designed performance of a building and allowing heat losses to take place.

Thermal bridging is prevented in buildings through the application of thermal insulation. Although, where an intumescent coating has been used, further consideration must be given to the wider thermal performance, resulting in the need to retrospectively install further insulating materials to navigate this challenge. Contractors must ensure that any additional measures applied do not detract from the fire performance of the intumescent coating.

To avoid delays to site programmes and simultaneously deliver fire protection, thermal and acoustic insulation, best practice is to consider how to satisfy these requirements from the design stage. One way this can be achieved is by cladding the structural steel beams using non-combustible insulation from the outset.

Stone wool insulation in particular, addresses additional specifications by offering structural fire protection, thermal performance and acoustic benefits in one solution.

Testing stability of structural steel systems

Although stone wool has the ability to satisfy wider building needs, when installing passive fire protection, product solutions are currently required to be tested in accordance with current EN standards.

The harmonised regulations were introduced by the Construction Products Regulation for the marketing of products across the EU, to ensure high safety standards for consumers. As a result, current UK product solutions are transitioning to the enhanced EN Standards being the more onerous, and contemporary testing regime.

Specifically in structural steel construction, the harmonised standards provide product manufacturers with a method that demonstrates a product’s ability to comply with relevant EU legislation.

The performance requirements examine various aspects of the product to measure its behaviour in application, and presumed conditions for the design and execution of fire protection.

When compared with the British standards, the EN testing scope provides improved and more stringent test conditions, ensuring products that pass are extensively tested and proven to perform for the intended application.

BS EN 13381-4, a far more recent standard when compared with BS 476 Part 21, tests a range of structural steel elements of varying sizes and loading with individual protection methods applied in order to obtain scope of performance. The tests have been designed to capture specific criteria in order to offer a more comprehensive analysis. As such, in comparison to its counterpart, BS EN 13381-4 collates a range of temperature data between 350-750°C to support structural modelling of steel sections based on specific limiting temperatures in application. This variance in test methodology is integral to understanding how structural steel elements will perform in situ, as dependent on mode of application, beams will have differing limiting temperatures and may fail at lower levels.

Importance of testing scope

When considering passive fire protection for structural steel buildings, having an awareness and understanding of the test conditions and product performance are integral to safeguarding the building in the event of a fire.

As such, being able to verify the product has been tested under appropriate and correct conditions is essential.

There are a number of ways in which performance can be verified and the suitability of the material determined. Assessments, classification reports, CE marking, and third party certification are examples of key documentation which should be available on request from the manufacturer. This documentation will be instrumental in providing architects, specifiers and contractors the exact parameters of product use, whilst demonstrating the product’s performance and understanding of its evidential results.

Installing insulation

Once a system has been specified, installation of structural passive fire protection is recommended to be undertaken by accredited or third party approved installers. Accredited or approved installers will have been independently assessed and audited to ensure their standards of workmanship and processes meet the minimum requirement levels.

Learning and training support is accessible through dedicated industry bodies, such as the ASFP, and UKAS accredited installer schemes are also available, such as third party installer scheme FIRAS.

As well as this, manufacturers of structural fire protection products can provide training and development sessions, if requested by specifiers, to educate stakeholders on specific product performance and application appropriation.

Helping to instil industry best practice, installers will be aware of a system’s performance in the event of a fire and will only work with systems that are tried, tested and comply. Forward planning and design allows for standard tested details to be specified and formulated into construction works, ensuring compliance of tested systems.

If a building requires any deviation from tested specification, guidance should be sought from a qualified fire engineer and, in some instances, may require additional support from the system manufacturer or even additional testing. Ensuring that fire protection is specified at the design stage can minimise the requirement for non-standard applications and can lower the risk to buildings.

Passive fire protection is integral in structural steel buildings. Ensuring the construction meets the requirements of ADB and the facility stays secure enough to allow for the egress of occupants and entry of firefighting teams is the driving requirement behind building design. That said, with increased focus on internal environments and a building’s acoustic and thermal performance, having a passive fire protection solution that delivers additional benefits from the outset can seamlessly navigate design challenges whilst balancing compliance criteria.

Cladding structural steel beams in non-combustible insulation, that has been tested to harmonised EN standards, can help to safeguard performance in the event of a fire and maintain performance during operation from an acoustic and thermal perspective.

 

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