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CROSS Safety Report

Beam and block floors fire resistance

Report ID: 1072 Published: 13 December 2021 Region: CROSS-UK


Overview

A report has been received about unsubstantiated claims of fire performance and the unavailability of test data for a specific form of construction.

Key Learning Outcomes

For designers and specifiers:

  • When using a system as part of a design solution, make sure that it meets the criteria necessary for the situation in which it is being used
  • Ensure that for every solution chosen, all product information related to performance claims is available

For manufacturers and suppliers:

  • Ensure that, for products that offer fire resistance, it is made clear if they provide all the necessary performance characteristics, including integrity, insulation
  • If these products do not provide the necessary characteristics, they should be clearly marked as not suitable in certain situations

For the construction team:

  • Consider introducing a quality assurance process that covers the correct use and installation of fire protection products and components

Full Report

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A report has been received about unsubstantiated claims of fire performance and the unavailability of test data for a specific form of construction.

Since the Grenfell fire, an architectural practice has been undertaking ‘due diligence' checks on all the products used in their designs. This includes locating all the test reports and data provided by manufacturers on products that have any fire performance requirement. It was a cause of shock to realise the lack of test data and the ‘quiet disappearance’ of fire resistance claims from product information in the market literature.

shock to realise the lack of test data and the ‘quiet disappearance’ of fire resistance claims from product information in the market literature

This report is on a project employing a beam and block flooring system. Such systems are comprised of concrete or steel beams upon which blocks are supported to form a slab. The blocks can be made out of concrete based materials or expanded polystyrene blocks when a thermal insulation function is desired. An indicative cross-section of such a system is shown in Figure 1 below.

beam and block construction cross section_free use
Figure 1: cross-section of a beam and block flooring system

Their usual field of application, according to the reporter, are as flooring on ground floor slabs in residential projects. However, the need arose for the same system to be used for the construction of upper floors due to site restrictions. This means that the floor will now be a compartment floor and has to satisfy the functional requirements regarding the limiting of fire spread and ensuring structural stability. The technical guidance in Approved Document in such cases recommends a fire resistance rating of 60 minutes in a furnace test.

The reporters claim that they enquired with manufacturers to substantiate some of their claims such as that “the concrete beams are ‘fire rated’ for either 30 or 60 minutes depending on depth” but were never provided with a test certificate that supported such claims, and when they insisted the general response was that “that’s someone else’s issue”.

Third Party Schemes

A source of further confusion was that such structural systems are presented in third party schemes that assure conformance with the requirements for Acoustics, and Approved Document E. The reporters employ the guidance of this scheme as part of their detailing work to satisfy requirements that ensure no need for site testing for Acoustics. This, to them, is an indication that such systems are being detailed for and constructed in multi-storey buildings, in which case they ought to have some role in the fire design and a performance rating is needed. The reporters implicitly assumed that by the inclusion of these systems in such handbooks “they must have some fire resistance”.

However, when the CROSS team investigated the aforementioned Approved Document, it was found that it did not deal with fire detailing issues, and instead directed the designers to the requirements of Part B of the Building Regulations. It follows that it explicitly deals with the requirements of Part E for Acoustics, and following this guidance is no guarantee that it satisfies Part B for Fire Safety.

Expert Panel Comments

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The reporters are correct in recognising and reporting the worrying trend of unavailable performance certificates, along with the inability of manufacturers to provide definitive answers.

A beam and block system may be supported by a number of structural forms such as, but not limited to, masonry walls, steel beams or frames, or other Reinforced Concrete or Precast Concrete beams and frames. It should have adequate fire resistance to meet the building regulations as part of a system – the latter includes any necessary additional fire protection such as ceiling boards or intumescent paints.

Past engineering standards, and now the Eurocodes, deal with fire requirements by prescribing the concrete cover to the reinforcement and minimum beam width, for simply supported beams, which can be an explanation of how some manufacturers’ claims originated. Fire resistance is a metric for three performance components; loadbearing capacity, integrity, and insulation. The practice of standard cover tables can address the loadbearing capacity of the beams but ignores the presence of blocks and their influence on the system performance in terms of integrity and insulation. Performance issues have to also be addressed with the block selected and the gaps between beams and blocks, which may or may not be filled. Finally, the choice of the ceiling finish, along with any lighting sockets, and the presence or absence of a floor screed, is needed to properly understand how the floor performs and the most appropriate construction methodology to be employed.

Gaining substantiation for manufacturers' claims

When in doubt about using beam and block products for upper floors, confirmation should be sought from the manufacturer that their product has been tested as a system (beam and block). This is the most formalised way to substantiate their claims in the absence of any secondary means of providing fire resistance. Designers and specifiers are encouraged to request the fire performance information of floor systems from their manufacturers and suppliers. This information could also be provided by a third-party approvals body or a ‘Notified Body’, which should be able to provide a confirmation of fitness for purpose. In any case, it is crucial that appropriate quality control should be ensured on-site so that the system is constructed according to the manufacturer’s specifications.

Design guidance for this form of construction is available and it provides three options for the calculation of fire performance:

  • Evaluation of a product or system by testing,
  • The use of calculation methods for resistance, integrity, and insulation,
  • The employment of available tabulated data.

However, the interpretation of a testing certificate, the use of simplified or advanced calculation methods, and the choice of the appropriate tabulated case are the remit of a fire engineer. The structural system chosen might appear simple, but fire testing and performance are not; hence the need for specialist advice. The fire strategy of a building should be conducted by a competent fire engineer, who will be able to assist in the navigation of the issues that arose within this report.

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