Concerns have been growing that the fire performance of some innovative construction systems is unknown or not properly understood. Debbie Smith introduces a new test standard, launched last month, which aims to provide more information on innovative construction methods.

The primary objective of LPS 1501 is to provide insurers, fire service and regulatory authorities with evidence that innovative building systems can maintain acceptable levels of fire performance in the event of a fire.

It has been developed by BRE Global to enable LPCB certification of innovative building systems in different building types, such as offices, hotels and schools in collaboration with and to address concerns of key industry stakeholders including insurers and the fire service. This standard provides a means of assessing performance for novel forms of building systems that do not have a proven track record in relation to performance in fire.

LPS 1501 covers these different building types by defining alternative nominal fire loads and floor loading, dependent on the intended use.

LPS 1501 has been developed to cover a range of different building types and a range of different applications. The principal objective of the standard is to identify modes of failure within the system that might prevent specific forms of construction (such as modular or panellised systems) from achieving the presumed performance in fire, based on regulatory compliance for structural elements with the current standard means of test and assessment. Potential weak links could include the premature failure of connections or a breach in compartmentation due to inadequate fire stopping.

The standard provides a performance and classification system for modern buildings based on the results of a full scale fire test. The objective of the test is to demonstrate the performance in a fire of innovative building systems. The performance relates to the interaction between floors and walls, fire stopping around openings and the correct functioning of cavity barriers in a purpose built test building. The current standard fire test procedures for elements of construction required for building regulation compliance do not generally consider interactions between different elements, or the performance of the system.

Test method
The test building comprises three individual units (see Figure 1) constructed with all internal and external finishes but excluding building contents. The test compartment is constructed with a similar unit adjoining the property connected through a party wall, and a similar unit above the fire compartment.

Figure 1 Basic layout for large scale fire test

The units adjoining and above the fire compartment will be lined in accordance with the manufacturer’s specification. The unit above will be loaded uniformly over the floor area to provide a value of imposed load, consistent with the fire limit state value appropriate for the specific occupancy. Each building unit will be supplied with cable and service penetrations appropriate to the end use.

Ventilation will be provided by unglazed windows within the fire compartment. The size and location of the windows will reflect, as far as reasonably practicable, the end use application. The fire load will be provided by a number of softwood cribs distributed uniformly on the floor of the fire compartment. Each crib will be ignited by applying a flame to strips of paraffin-soaked porous fibre board. The fire load density (fire load per unit area of floor) will be specified by LPCB and will be dependent on the nature of the occupancy.

Measurements during the test will include atmosphere temperatures within the fire compartment, the surface temperature of the unexposed face of the party wall and the surface temperature of the floor above the fire compartment. Additional temperature measurements will be made on either side of all cavity barriers to assess performance. Additional instrumentation may be installed at the request of the manufacturer to provide information on the response of the floor, wall and connecting elements.

Performance and classification
The performance of the system will be evaluated in relation to integrity, insulation and stability criteria. The integrity of the building system will be demonstrated if the fire is restricted to the compartment of origin for the duration of the test. Any break through of the fire into the adjoining units will constitute a failure. The insulation criteria will be met if the temperature on the unexposed surface of the party wall or the floor of the unit above remain below an average value of 140ºC and a peak value of 180ºC for the duration of the test. The stability criteria will be met if the floor above continues to support the applied load for the duration of the test, or exhibits deflections not exceeding span/20 for the duration of the test.

To assist with regulatory compliance and to provide information in a language understood by many building professionals, the severity of the natural fire exposure shall be evaluated with respect to an equivalent period in a standard fire test. The equivalent period of fire resistance will be determined either by calculation or direct measurement, or a combination of the two.

Performance will be classified with reference to grades relating to the specific purpose group(s) against which the construction system has been assessed.

The introduction of LPS 1501 will assist key stakeholders, including the fire service, regulatory authorities and insurance companies in the commercial property sector, by providing a credible property based fire performance test for innovative methods of construction. Specification of LPS 1501 approved building systems will provide interested parties with a high degree of confidence that the buildings in question achieve satisfactory levels of fire performance over and above that required for compliance with the minimum standards of the Building Regulations for life safety.

Debbie Smith is director of fire sciences at BRE Global