LPS 1107: Issue 1.2 Requirements, tests and methods of assessment of passive fire protection systems for structural steelwork
Fire Protection System
For the purposes of this document, the term “fire protection system” refers to the product and the method of fixing or retaining the product around the structural steel element.
Stickability
For the purposes of this document, the term “stickability” refers to the ability of a fire protection system to remain fixed in position during the fire test.
Critical Temperature
For the purposes of this document, the term “critical temperature” refers to the temperature at which a structural element is assumed to fail to support the applied load. The critical temperature of an element varies with the magnitude of the applied load.
Test Specimens
For the purposes of this document, the term “test specimen” refers to the beams, columns and fire protection system which were used to evaluate the performance of a fire protection system.
Passive Fire Protection Systems
For the purposes of this document, the term “passive fire protection system” refers to board, blanket and spray/trowel applied systems other than intumescent coatings.
Section Factor
For the purposes of this document, the term “section factor” is defined as the ratio of the heated perimeter to section area.
Heated Perimeter
For the purposes of this document, the term “heated perimeter” of a section is defined as the inside perimeter of a fire protection system. For box protection systems the heated perimeter is the perimeter of the smallest rectangle that encloses the steel section.
Fire Resistance
The relevant British Standard for testing structural steel elements protected by proprietary products is BS 476: Part 8: 1987, Part 20, 21: 1987. The performance of any product will be judged against this standard. All tests shall be carried out by a NAMAS accredited laboratory acceptable to the LPCB.
A limited number of tests (see Tables 1 and 2) on loaded beams and columns are required, supported by additional data obtained from unloaded sections and the results interpreted to give protection thicknesses for the full range of steel sections. See section 6 for further details.
Loaded beams and columns shall be loaded to their maximum permissible stresses in accordance with BS 449: Part 2: 1969.
For assessment purposes, a mean steel temperature at failure (critical temperature) of 550°C is assumed for beams and columns. The mean steel temperature is defined as:
(mean lower flange temperature + mean web temperature)/2.
Adequate stickability of the fire protection system shall be demonstrated at the maximum and minimum proposed thicknesses.
Specification for Tests
Fire tests shall be performed on loaded sections in accordance with BS 476 : Part 8 : 1972, Part 20 and 21: 1987 as specified in para 4.2.1. Unloaded sections shall be subjected to the heating regime of BS 476: Part 8 (1972), Parts 20 and 22, 1987.
Measurement of Steel Cross-Section of Test Specimens
The steel section shall be measured with position as shown in Figure 1 at a minimum of two sections.
Steel thicknesses shall be measured to an accuracy +0.1mm and the depth and width of the sections shall be measured to an accuracy of within +0.5mm.
The mean values of the depth of section (D), width of section (B), flange thickness or
Wall thickness (T) and web thickness (t) shall be quoted, where applicable, in the test report.
The section factor for a specimen shall be calculated using the actual steel sizes and ignoring the root radii. For boxed protection systems, the section factor is calculated from the heated perimeter. See figure 2 for examples.
Specimen Preparation and Application
The steel preparation techniques shall be representative of practice.
The fire protection system shall be representative of that used in practice.
The specimens shall be in the same orientation as expected in practice during the application of the fire protection systems.
The protection thickness of spray materials applied to the test specimens shall not vary by more than +15%. of the mean value.
The density of a product shall not vary by more than +15% of the mean value.
Conditioning of Test Specimens
Specimens and sample, as defined below, shall be conditioned approximate to the state of strength, state of cure and moisture content that would be expected to occur in practice.
To ascertain if a product is fully conditioned for test, a representative sample at least 300mm x 300mm of maximum thickness shall be weighed regularly until its weight stabilizes before a specimen is tested.
If a specimen is force dried at temperatures above 30°C and relative humidities below 50%, the forced drying shall be terminated a minimum of 2 weeks before the specimens are tested. The specimen shall not be tested after this period until the weight of a representative sample has stabilized.
The moisture content of a representative sample of the product (if appropriate) shall be estimated by oven drying the sample between 100°C and 105°C. If a material is known to loose combined water below 100°C, it may be oven dried at lower temperatures before being oven dried at 100-105°C. Both values shall then be quoted in the test report.
Size of Specimens
Unloaded columns shall be a minimum of 1.0m high.
Unloaded beams shall be a minimum of 1.2m long.
Instrumentation of Unloaded Specimens
The temperature of the unloaded specimens shall be measured by chromel/alumel thermocouples. The thermocouples may be ‘peened’ to hold them in position by drilling holes in the specimen slightly larger than the thermocouple and deep enough to accommodate the junction, and burring the edge of the hole. For structural hollow sections, the thermocouple junction shall be peened to steel plugs of the same thickness
as the section wall. The plug shall then be secured in a hole drilled in the section wall, and the thermocouple leads run through the inside of the section.
The thermocouple leads shall be run from the furnace without significantly affecting the fire protection system.
Five thermocouples shall be fitted to the unloaded columns (three on the flanges and two on the web of I-section columns). The positions of the thermocouples for I-section, rectangular and circular hollow section columns are shown in Figure 3. Additional thermocouples can be used.
Six thermocouples shall be fitted to the unloaded beams (four on the lower flange and two on the web on I-section and rectangular section beams are shown in Figure 4. Additional thermocouples can be used.
Additional thermocouples shall be applied if required by the LPCB to examine features of a specific fire protection system.
The temperature of the unloaded specimens shall be measured at intervals not exceeding 1 minute during the fire test.
Application Techniques
The fire protection shall be applied in accordance with section 5.1.3. Additional protection may be applied to the ends of the unloaded specimens to reduce end effects.
Unloaded columns shall be protected on four sides.
Unloaded beams shall be protected on three sides, the protection finishing flush with the top side of the upper flange (Figure 5).
Location of Specimens in Furnace
Unloaded columns shall be positioned in the furnace to ensure four-sided exposure. If the columns are placed on the floor on the furnace, the column bases shall be protected by sand or similar material to a maximum height of 150mm.
Unloaded beams shall be fitted to the roof of the furnace with a mineral fibre or ceramic fibre gasket fitted to the top flange of the beams (Figure 5).
Observations
The specimens shall be visually examined at regular intervals during the test. Note shall be made of the time at which cracks form or material becomes detached from a specimen.
Termination of Test
The test shall not be terminated until the mean web and mean flange temperatures of all the sections have exceeded 550°C.
The test may be continued beyond the 550°C limit to obtain additional information. 5.3 Test Procedures for Unloaded Sections
The test procedures of BS 476: Part 8: 19721, Part 20, 21: 1987 shall be adopted for testing loaded specimens. The specimens shall be loaded to induce maximum permissible stresses in accordance with BS 449: Part 2: 1969 during the fire test.
Additional procedures, not specified in BS 476 : Part 8 : 19721, Part 20, 21 : 1987 are detailed in sections 5.3.2 – 5.3.5.
Beams shall normally be tested, simply supported with an exposed length of 4m. A concrete slab approximately 920mm x 130mm deep shall be cast on top of the beam which shall not contribute significantly to the strength or stiffness of the steel beam. A specification for a suitable concrete slab and method of attachment to a steel beam is given in Appendix 1.
Columns shall normally be tested with an exposed length of approximately 3.1m. The columns shall be axially loaded and the column ends shall be effectively restrained against rotation.
Typical details showing a suitable method of supporting a column during a fire test are given in Appendix 2.
Instrumentation of Loaded Specimens.
In addition to the requirements of BS 476 : Part 8 : 1972, Part 20, 21: 1987 the temperature of the loaded specimens shall be measured by thermocouples attached to the specimen as described in sections of 5.2.2.
Nine thermocouples shall be fitted to loaded I-section beams, five on the lower flange and four on the web in the positions shown in Figure 6. The position of thermocouples on rectangular hollow section beams are also shown in Figure 6.
Ten thermocouples shall be fitted to the loaded I-section columns, six on the flanges and four on the web in the positions shown in Figure 7. The position of thermocouples on rectangular hollow section and circular hollow section columns are also shown in Figure 7.
Additional thermocouples shall be applied if required by the LPCB to examine features specific to a fire protection system.
The temperature of the loaded specimens shall be measured at intervals not exceeding 1 minute during the test.
Application Techniques
The fire protection shall be applied in accordance with section 5.1.3. The loaded columns shall be protected on four sides. The loaded beams shall be protected on three sides.
The specimens shall be visually examined at regular intervals during the test. Note shall be made of the time at which cracks form or the material becomes detached from the specimen.
The test on a loaded beam shall not be terminated before the deflection has reached a value of L/35 where L is the clear span.
The test on a loaded column shall not be terminated before the rate of expansion of the column becomes negative.
Once the limits specified above have been reached, the test may be continued with the load reduced
To obtain an assessment establishing the relationship between protection thickness, section factor and fire resistance, the conditions in paragraph 6.2.2 shall be satisfied.
The test programme shall be designed and the assessment made by LPCB personnel.
The techniques specified below are based on methods developed by the Fire Research Station, Borehamwood.
The assessment shall be based on insulation data obtained from unloaded sections, supported by tests on beams and columns.
A multiple linear regression method shall be used to interpolate the relationship between section factor, fire resistance and protection thickness assuming a critical steel temperature of 550°C.
Selection of Test Specimens for Assessment of a Fire Protection System on I- Sections and Sections with Re-entrant Detail
Selection of Test Specimens for Assessment of a Fire Protection System Applied to Structural Hollow Sections and Sections Without a Re-Entrant Detail
Where a fire protection system is intended to be used in sections without re-entrant details (e.g. structural hollow sections), further testing is required if in the opinion of the LPCB the change of section shape is considered to significantly affect the performance of the system.
For spray materials the use of wire mesh on sections without re-entrant details may be permitted at the discretion of the LPCB. Reference shall be made to Fire Protection for Structural Steel in Buildings3 and Code of Practice for sprayed mineral insulation BS 8202: Part 1: 1987 for further information.
If an I-section assessment package has been successfully completed on a boxed fire protection system, the required protection thicknesses may be assumed to be the same for I-sections and structural hollow sections (SHS) having the same section factor.
For fire protection systems contoured to the steel section the following equation may be used to calculate a factored section factor from which the thickness of protection required for a SHS may be calculated from data obtained from I-sections.
section shapes.