BR135: Annex B Performance criteria and classification method for BS 8414-2:2005

Digest 501

Sarah Colwell

BRE Certification

BR 13 5: Fire performance of external thermal insulation for walls of multi­storey buildings was published in 2003 and Annex A: The performance criteria and classification method of BS 8414-1 :2002, was published as part of this revised edition.

This Digest contains Annex B to BR 13 5 which provides a classification system for the test methodology outlined in BS 8414-2:2005 Fire performance of external cladding systems- Part 2: Test method for non-loadbearing external cladding systems fixed to and supported by a structural steel frame.

Test method

Background Following the publication ofBS 8414-1 :2002 Fire performance of external cladding systems-Part 1: Test method for non-loadbearing external cladding systems applied to the face of a buildinf.!Bl] and the subsequent revision in 2003 ofBR135 Fire performance of external thermal insulation for walls of multi-storey buildings[B2

J to include a classification system for this test methodology, it became apparent that the technology being utilised for the construction of cladding and external wall systems was developing in such a way that the Part 1 test method was no longer appropriate for assessing the fire performance of design details and systems which utilise framed structures. This resulted in the publication ofBS 8414-2:2005 Fire performance of external cladding systems-Part 2: Test method for non-loadbearing external cladding systems fixed to and supported by a structural steel frame. [B3J In order to support this test method the classification system described in this Digest has been developed.

Figure 81 A typical test facility

Principle of test

This test was taken from the scope ofBS 8414-2:2005). [B3J The test facility has been designed to determine the external fire performance of non­loadbearing external cladding systems, such as curtain walling, glazed elements, infill panels and insulated composite panels, and site assembled cladding systems fixed to, and supported by, a structural steel frame. Figure B 1 illustrates a typical test facility.

The principle purpose of the test methodology is to enable the overall fire performance of the system, and its relevant components, to be assessed as a complete system test as far as is practically possible. The test facility allows external cladding systems to be installed close to typical end-use conditions and allows variations in the steel frame design to match those used in practice, if required. As inBS 84141: 2002,[BlJ the

test frame consisted of a vertical main test face, into which the combustion chamber is located, and a vertical return wall or wing, set at 90° to the main

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test face. The test specimen is installed to represent typical end use applications. The test specimen extends a minimum of 6 m above the combustion chamber opening on the main face and is at least 2.8 m wide. The return wall or wing is the same height as the main test wall and is a minimum of 1.5 m wide. The distance between the surface of the cladding on the wing and the edge of the combustion chamber opening is 260 (+0 -100) mm (see Figure B2).

The ignition source used inBS 8414-2:2005[B3] is the same as that prescribed in BS 8414-1 :2002,[B 1] ie either a

~2800

Main face

Wing

Combustion chamber

~11-2000+100 0

260-100 I

~6000

r 2000±

_l 100

I! l\46'1

Section A

wooden crib (as specified in Annex C ofBS 8414-1 :2002)[B 1] or a gas burner meeting the characteristics set out in Annex B ofBS 8414-1 :2002.[B 1]

The full details of the test method can be found in BS 8414-2:2005,[B3] and while the definitions are shown for reference, in all cases the interpretation of test results should be made with full regard to BS 8414-2:2005.[B3] Figures B2, B3 and B4 show schematics of the test facility and thermocouple locations.

Section B

Section c

I 31oo I

~- - ~±o

1

A c A

Section Nominal detail reference

A 254 x 146 x 11 Universal beam

B 150 x 150 x 6.3 Steel hollow section

c 127 x 54 x 9 Pre-formed channel

D so x so x 6 Rolled steel angle

80 .~1 I-

80[F

t Section

D

Mass per unit length (kg/m)

37.0

2S.3

14.9

9.63

Figure 82 Schematic of typical test facility and frame (dimensions in mm)

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Instrumentation As defined in BS 8414-1 :2002[BlJ and outlined in Annex A of BR13 5, [B2J Type K thermocouples are used to monitor temperature at two array locations within the system under test. Figures B3 and B4 indicate the locations of the thermocouples used to monitor the temperatures during the test. At level2 (see Figure B3) the thermocouples are

Centre line of combustion chamber opening

500 500 F2

450 ---~~~ -['... 1-

I

l"-150~ I ........... I

I I

I I

I I

+ I + + + + + +

Wing Main face

+ + + + + + +

Combustion chamber

V

+

+

Tolerance thermocou

on pie

± 10 locations

I Level 2

2500

j

1

Level 1

2500

j

Figure 83 Location of thermocouples (dimensions in mm)

Non-e insula

Thermocouples

ombustible ....__ tion

Lightw eight frame_

1--

r--

7 Cavity

\

._____

\ Non >10

Combustible <10 mm

-combustible mm

Combustible insulation

Figure 84 Typical thermocouple locations through the wall at level 2

3

positioned at the mid-depth of each combustible layer, that is greater than 10 mm thick, where combustible is defined as a " ... layer incorporated in the construction product which, if tested in isolation, would fail the non-combustibility definition in Approved Document B Fire safety."[B4

J

Thermocouples are also located at the mid-depth of any cavity that may be present (see Figure B4 ).

Performance criteria and classification

method The following performance criteria and classification method are based upon the BS 8414-2:2005[B3J test method. As explained in Annex A ofBR135, [B2J the primary concern when setting the performance criteria for these systems is the fire spread away from the initial fire source and the rate of fire spread. If fire spread away from the initial fire source occurs, the rate of progress of fire spread or tendency for collapse should not unduly hinder intervention by the emergency services. The performance of the system under investigationis evaluated, against the following three criteria: e External fire spread e Internal fire spread e Mechanical performance.

Fire spread start time, t5

Fire spread is measured by type K thermo-couples set at levels 1 and 2 (see Figure B3). The start time, t,, for fire spread occurs when the temperature recorded by any external thermocouple at level1 equals or exceeds a 200 oc temperature rise above the start temperature, T,, and remains above this value for at least 30 seconds. An example graph is shown in Figure B5, this is also shown as Figure AS in BR135 Annex A[B2J and is repeated here for reference, where ignition of the heat source corresponds to time zero.

Definitions

Level1

A height 2.5 m above the top of the combustion chamber opening

(Figure B3).

Level2

A height 5 m above the top of the combustion chamber opening

(Figure B3).

Start temperature, T5

The mean temperature of the thermocouples at level1 (Figure B3)

during the five minutes before ignition.

Start time, t5

The time when the temperature recorded by any external

thermocouple at level1 equals or exceeds a 200 oc temperature

rise above T5

, and remains above this value for at least 30

seconds (Figures B3 and B5).

System

The complete cladding assembly, including any sheeting rails,

fixings, cavities, fire barriers and weathering membranes or

coatings.

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500 r-- The level 1 thermocouple exceeded a

C1J 400 r--200oC temperature rise 5. 7 minutes

(f)

·.:::: after ignition of the heat source.

r-- Start time ts = 5. 7 minutes /\ ~ 300 Start temperature T s = 22oC

" :.1 \I --::J +' (IJ .... gs_ 200 ~~

}V"" "'V

~ I

E ~ 100

./.' 2 4 6 8 10

Time (minutes)

Figure 85 Level1 thermocouple used to determine start time t5

800~--~------------r===============~ The level 2 data is plotted with

1-----+-----"- -M /"1.------ithe origin for the time axis <ll 600 I V I passing through Start time ts. <JJ ------t-- In this example level 2 ·;:: thermocouple exceeded 600oC 2:' \ temperature rise 12.7 minutes ~ 400 I after ts and therefore failed to m / \ meet the performance criteria

Q_ / '""' ~ 200 f---1-----i"--/ ---------\-~--~--.tl----1

0~--~/~~----~----~--~----~--~ -10 0 10 20 30 40 50

Time (minutes)

Figure 86 Level 2 thermocouple plotted with start time set to time zero

External fire spread Failure due to external fire spread is deemed to have occurred if the temperature rises above T, of any of the external thermocouples at level2 exceeds 600 °C, for a period of at least 30 seconds, within 15 minutes of the start timet,. An example graph is shown in Figure B6, this is also shown as Figure A6 in BR135 Annex A and is repeated here for reference.

Internal fire spread Failure due to internal fire spread is deemed to have occurred if the temperature rise above T, of any of the internal thermocouples at level2 exceeds 600 °C, for a period of at least 30 seconds, within 15 minutes of the start timet,. An example graph is shown in Figure B6, this is also shown as Figure A6 inBR135 AnnexA[B2J and is repeated here forreference.

Mechanical performance Details of any system bum through, collapse, spalling, de lamination or flaming debris should be included in the test report. Whilst system collapse, spalling, de lamination or flaming debris are not considered to be failure criteria, the nature of the failure should be considered as part of the overall risk assessment when spec­ifYing the system.

Where system bum through occurs so that fire reaches the internal surface, failure is deemed to have occurred if continuous flaming, defined as a flame with a duration in excess of 60 seconds, is

observed on the internal surtace ofthe test specimen at or above a height of0.5 m above the combustion chamber opening within 15 minutes of the start time ts.

References [B1] British Standards Institution, 2002. BS 8414·

1 :2002. Fire performance of external cladding systems

-Part 1: Test method for non-loadbearing external

cladding systems applied to the face of a building.

[B2] BRE, 2003. BR135 Fire performance of external

thermal insulation for walls of multi-storey buildings.

Garston, Watford, BRE Bookshop.

[B3] British Standards Institution, 2005. BS 8414·

2:2005. Fire performance of external cladding systems

-Part 2: Test method for non-loadbearing external

cladding systems fixed to and supported by a structural

steel frame.

[B4] Department of Communities and Local

Government, 2006. Approved Document B Fire safety.

Volume 1 Dwelling houses.

Acknowledgements

We would like to express our thanks to the Department

of Communities and Local Government for funding this

project.

Permission to reproduce extracts from BS 8414-2:

2002 is granted by BSI.

(British Standards can be obtained from BSI Customer

Services, 389 Chiswick High Road, London W4 4AL. Tel: ­

- mail: cservices®bsi-global.com)

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