LPS 1501 Issue 1.1 Fire test and performance requirements for innovative methods of building construction
This Standard provides a specification for fire testing and classification of innovative building systems used for building construction in the UK.
The standard is intended to include the following types of building systems:
Hybrid systems Panellised systems Volumetric systems
For the purposes of this standard, the following definitions taken from “Modern methods of house construction – A surveyor’s guide” by K Ross shall apply:
Closed panel systems
Types of panellised systems that can have services, windows, doors, internal wall finishes and external claddings fitted in a factory.
A combination of both volumetric and panellised systems.
Open panel systems
Types of panellised systems that comprise a framing system delivered to site before insulation, services etc are fitted.
Flat panel units produced in a factory that are transported to site for assembly. These include open panel systems and closed panel systems.
Three – dimensional units produced in a factory. All necessary internal finishes, services and potentially furnishings can be installed at the factory. However, furnishings or contents are outside of the scope of this standard.
PERFORMANCE IN FIRE
The requirements given below are specifically in relation to the method of test described in this standard. The basis for performance criteria are;
- to minimise the effect of fire on the building itself;
- to limit the effects of interruption to the use of a building;
- to allow the building to be re-occupied as soon as possible after a fire incident.
Passive fire protection requirements
The building system shall have adequate fire protection to prevent collapse or partial collapse and exhibit restricted deflections.
The building system shall be constructed in such a manner that, if a fire starts, the extent of fire and smoke damage will be minimised. Fire shall not enter into an adjoining property and shall, as far as possible, be prevented from entering concealed cavities or roof voids. If fire does enter any cavities or voids, its spread shall be minimised by appropriate design and /or fire protection measures. Consideration shall be given in the design of the building to limit the spread of smoke into adjoining properties.
Note: although smoke densities are not measured as part of this test and do not form part of the acceptance criteria, fire spread routes will provide a good indicator of potential smoke spread routes.
Active fire protection systems
The building system shall comply with the acceptance criteria in clause 4.2 without any active protection during the test.
Full-Scale Natural Fire Test
Due to the inherent risks involved with large scale fire tests, great care shall be taken at all stages of the procedure (including, but not exclusive to, build and preparation, loading and unloading, test, monitoring and inspection, and dismantling). A full risk assessment and method statement shall be prepared and agreed by all parties for each system test undertaken.
In order to demonstrate performance in fire of innovative building systems, including the interaction between floors and walls, fire stopping around openings and the correct
functioning of cavity barriers, the full-scale test described in this standard is required. LPCB shall advise the manufacturer of the precise specification for the test so as to obtain the broadest application from the results, but taking into account the generic configuration described in 4.1.2. This is normally interpreted to select the specification that is anticipated to achieve the lowest level of performance.
The test building shall comprise 3 building system units (see figure 1). It shall be constructed with its intended internal and external finishes but excluding any contents including floor coverings or furnishings. The overall dimensions of the test compartment will be representative of the intended end use application and will simulate the accommodation area of one floor of a single building system unit. The test compartment will be constructed with a similar building system unit adjoining the property connected through a party wall and a similar unit above the fire compartment.
The units adjoining and above the fire compartment will be lined in accordance with the manufacturer’s requirements. The unit above will be loaded uniformly over the floor area to provide a value of imposed load as defined in 4.1.6. Each building system unit shall be supplied with cables and service connections and penetrations appropriate to the intended end use.
Ventilation shall be provided by unglazed window openings usually on the front elevation of the test building. Their size and location will reflect normal building practice and will be typical for the intended end use application. Door openings shall be provided for access and
egress to the test building, the number and location of these door openings shall be determined in consultation with LPCB prior to building the test buildings. The ventilation conditions operable during the fire test will be determined by LPCB in order to provide the relevant ventilation requirements for the given fire load, however this will, as far as is practical reflect the situation related to the end use application. Prior to the fire test, shut doors shall be sealed by plasterboard.
Fire load / Ignition source
The fire load for the test shall comprise a number of softwood cribs distributed uniformly on the floor of the fire compartment. Each crib shall consist of rough sawn lengths of kiln dried Redwood/Scots Pine or similar softwood sticks each 50mm x 50mm x 1000mm long *. The timber sticks shall be laid with alternate layers arranged mutually perpendicular in a crisscross fashion. The timber sticks shall be spaced 50mm apart in each layer. The moisture content of the timber shall be measured prior to testing and shall be in the range of 7-13%. Cribs shall be equally spaced over the entire floor area and be a minimum of 300mm apart from each other. Consideration shall be given to suitable and safe access for ignition.
* Note; the length of the sticks may be reduced to a minimum of 500mm should the size of the test building be such that longer sticks cause problems with loading, however the nominal fire loads described below shall be maintained.
Each crib shall be ignited by applying a flame to strips of paraffin-soaked fibre insulation board (12mm x 12mm section) connecting each crib to the adjacent cribs and positioned between the lower two layers.
The crib specification shall be calculated by LPCB to represent a nominal fire load as indicated in table 1 based on the floor area and the intended end use of the building system (see Appendix A).
Table 1. Nominal fire load applicable to different purpose groups.
For purpose groups not included in the table, the appropriate fire load density will be determined through a specific fire engineering risk assessment. For grading purposes, some of the fire loads given above are not used (see clause 4.5).
Internal atmosphere temperatures shall be measured 100mm and 300mm below the ceiling of the fire compartment using 1.5mm diameter stainless steel sheathed thermocouples (or equivalent in terms of response time) with at least one location per 2m2 of ceiling area.
Temperatures of the outer surfaces of the fire compartment (internal surface of adjoining compartment and floor surface of the compartment above) shall be measured using thermocouples of the type specified in BS476: Part 20: 1987 (Method for determination of the fire resistance of elements of construction) for measuring the temperatures of the unexposed surface of partitions/roofs. They shall be positioned on the surface of the wall and floor above with at least 5 on each element to measure mean temperatures. Additional temperature measurements shall be required on both sides 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 floor (joists), wall (studs) and connecting elements.
Subject to the agreement of LPCB, instrumented indicative protected steel elements may also be placed within the centre of the fire compartment (supported on protected steel trestles) to provide information on the time equivalent value of the fire in relation to an equivalent period in a standard test furnace (see Appendix B2).
A photographic and video recording of the fire test shall be provided by the test laboratory. This shall include video coverage of the internal aspects of the adjoining test buildings with one or more cameras positioned to monitor the compartment wall/floor as applicable.
The floor of the compartment above the test compartment shall be loaded to provide a uniformly distributed load equal to:
Table 2. Compartment floor loadings
Full-scale natural fire test procedure
The test shall be conducted under cover to avoid variations due to weather. Ambient temperatures shall be between 5°C and 25°C.
18.104.22.168 Start of test
The test shall be started by igniting the timber cribs simultaneously or in succession, provided that all of the cribs are ignited within 60 seconds.
- Gas temperatures
Gas temperatures shall be recorded continuously or at intervals not exceeding 30 seconds. Surface or component temperatures shall be recorded at intervals not exceeding 1 minute.
Integrity shall be monitored throughout the test by visual inspection to record any signs of flames outside the compartment of origin.
- End of test
The fire shall be allowed to burn out and the test continued until conditions have stabilized. Any residual burning embers can be extinguished at this point.
Note: The laboratory shall reserve the right to end the test at any time if there is considered to be any risk to the health and safety of the persons or property involved in the test.
Fire breaking through windows shall not be taken as failure under the criteria given below:
The integrity of the building system shall be demonstrated if the fire is restricted to the compartment of origin for the duration of the test.
- Adjoining building system units
Any break through into the adjoining building system units will constitute a failure and will be recorded with respect to the time from ignition.
Any break through into any cavity will be assessed in terms of restricted extent of damage. Spread beyond the cavities immediately adjacent to the compartment of origin (wall or floor (not both)) will constitute a failure.
The insulation criteria shall be met if the temperature on the unexposed surface of adjoining building system units, i.e. the party wall and the floor of the compartment above, remains below an average value of 140°C and a peak value of 180°C.
The load bearing capacity of the building system shall be met if the floor above continues to support the applied load for the duration of the test or exhibits deflection not exceeding span/20.
Equivalent time of fire exposure
In order to assess performance, the severity of the natural fire shall be evaluated with respect to an equivalent period in a standard fire test. The equivalent period of fire resistance shall be determined either by calculation or direct measurement in accordance with Appendix B..