[piwniczak]

As a result of the fire at Knowsley Heights, Approved Document B Fire Safety (ADB) 1992 was changed so that fire performance ‘Class 0′ [Class 0 - najwyzsza klasa odpornosci na ogien, Class 0 stosuje sie np. na przeciwpozarowych drogach ewakuacyjnych - dop @piwniczak] applied to the inside (cavity) face as well as the outside of rainscreen cladding systems on ‘tall’ (>20m) buildings:

“ 12.6 In the case of the outer cladding of a wall of ’rainscreen’ construction (with a drained and ventilated cavity) the surface of the outer cladding which faces the cavity should also meet the provisions of Diagram 36.” (i.e. Class 0 rainscreen cladding recommended above 20m height and/or within 1m of site boundary) (ADB 1992)

There has also been advice regarding combustibility of insulation materials in cladding in ADB ever since 1992:

“ 12.7 The external envelope of a building should not provide a medium for fire spread if it is likely to be a risk to health or safety. The use of combustible materials for cladding framework, or of combustible thermal insulation as an overcladding or in ventilated cavities, may present such a risk in tall buildings, even though the provisions for external surfaces … may have been satisfied.

In a building with a storey at more than 20m above ground level, insulation material used in the external wall construction should be of limited combustibility …” (ADB 1992)

ADB 1992 also recommended that the voids within rainscreen cladding be closed by cavity barriers. The definition of a cavity barrier in 1992 was “ A construction provided to close a concealed space against penetration of smoke or flame, or provided to restrict the movement of smoke or flame within such a space.” UK guidance makes a distinction between a cavity barrier and a fire stop, which is defined as “ A seal provided to close an imperfection of fit or design tolerance between elements or components, to restrict the passage of fire and smoke.”

ADB 1992, Table 13 Provision of cavity barriers, recommended that for flats, other residential (including hotels) and institutional buildings, i.e. places where people sleep, cavity barriers were to be provided within the void behind the external face of rainscreen cladding at every floor level, and on the line of compartment walls abutting the external wall, of buildings which have a floor more than 20m above ground level. (ADB 1992) In the complete re-drafting of the 1985 edition of ADB, the earlier advice to close the perimeter of cavities, including around door and window openings, was omitted in 1992. The recommendation was re-introduced in ADB 2000, for all building types.

Building Regulation requirements are not retrospective, so there was a legacy of buildings that did not comply with the new guidance.

The Knowsley Heights fire also motivated research at the Building Research Establishment (BRE), carried out in 1994. BRE developed a large-scale fire test method, known as ‘A test for assessing the fire performance of external cladding systems’, submitted to the government in 1996.

Subsequently, as a response to the Sun Valley fire, Appendix F: Fire behaviour of insulating core panels used for internal structures, concerning composite panels, was included in the 2000 edition of ADB, largely as a result of pressure from the fire service. Although subsequently revised, the advice was and still is directed at internal structures, but explains the fire behaviour of composite core materials and fixing systems which is common to external cladding also: [35]

“ 2. The degradation of polymeric materials can be expected when exposed to radiated / conducted heat from a fire, with the resulting production of large quantities of smoke.

It is recognised that the potential for problems in fires involving mineral fibre cores is generally less than those for polymeric core materials.

In addition, irrespective of the type of core material, the panel, when exposed to the high temperatures of a developed fire, will tend to delaminate between the facing and core material, due to a combination of expansion of the membrane [i.e. metal facing] and softening of the bond line.

Therefore once it is involved, either directly or indirectly in a fire, the panel will have lost most of its structural integrity. The stability of the system will then depend on the residual structural strength of the non-exposed facing, the interlocking joint between panels and the fixing system.

Most jointing or fixing systems for these systems have an extremely limited structural integrity performance in developed fire conditions. If the fire starts to heat up the support fixings or structure to which they are attached, then there is a real chance of total collapse of the panel system.

The insulating nature of these panels, together with their sealed joints, means that fire can spread behind the panels, hidden from the occupants of occupied rooms/spaces. This can prove to be a particular problem to firefighters as, due to the insulating properties of the cores, it may not be possible to track the spread of fire, even using infra-red detection equipment. This difficulty, together with that of controlling the fire spread within and behind the panels, is likely to have a detrimental effect on the performance of the fixing systems, potentially leading to their complete and unexpected collapse, together with any associated equipment.

Firefighting

3. When compared with other types of construction techniques, these panel systems therefore provide a unique combination of problems for firefighters, including:

hidden fire spread within the panels;

production of large quantities of black toxic smoke; and

rapid fire spread leading to flashover.

These three characteristics are common to both polyurethane and polystyrene cored panels, although the rate of fire spread in polyurethane cores is significantly less than that of polystyrene cores, especially when any external heat source is removed.

In addition, irrespective of the type of panel core, all systems are susceptible to:

delamination of the steel facing;

collapse of the system; and

hidden fire spread behind the system.” [36]

Following the Garnock Court fire, a parliamentary inquiry was undertaken to investigate the potential risk of fire spread in buildings by way of external cladding systems. The report was published early in 2000. [37]

Witnesses to the inquiry (including the Fire Brigades Union, Loss Prevention Council [technical advisers to the insurance industry], manufacturers of external cladding systems and independent fire safety consultants) suggested that the guidance given in Approved Document B might not be adequate for the purposes of ensuring the safety of external cladding systems in a fire. [38]

The committee concluded:

“18. The evidence we have received during this inquiry does not suggest that the majority of the external cladding systems currently in use in the UK poses a serious threat to life or property in the event of fire. …

19. Notwithstanding what we have said in paragraph 18 above, we do not believe that it should take a serious fire in which many people are killed before all reasonable steps are taken towards minimising the risks. The evidence we have received strongly suggests that the small-scale tests which are currently used to determine the fire safety of external cladding systems are not fully effective in evaluating their performance in a ‘live’ fire situation. As a more appropriate test for external cladding systems now exists, we see no reason why it should not be used.

20. We believe that all external cladding systems should be required either to be entirely non-combustible, or to be proven through full-scale testing not to pose an unacceptable level of risk in terms of fire spread. We therefore recommend that compliance with the standards set in the ‘Test for assessing the fire performance of external cladding systems’, which has been submitted to the British Standards Institution for adoption as a British Standard, be substituted in Approved Document B for previous requirements relating to the fire safety of external cladding systems.”

The BRE full-scale fire tests were developed to become:

BS 8414-1: 2002 – Fire performance of external cladding systems.

Test method for non-loadbearing external cladding systems applied to the face of a building.

BS 8414-2: 2005 – Fire performance of external cladding systems.

Test method for non-loadbearing external cladding systems fixed to and supported by a structural steel frame.

The test applies to whole cladding systems with all components, which may include fire barriers of non-combustible material to close any cavity and may also form a continuous band through the insulation, which in practice would be installed at each floor level. The test method simulates a fully developed fire in a room abutting the external face of a building and venting through a window aperture. 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. [39]

The specimens of cladding systems tested must have a minimum extent of 1.2m x 2.4m, in an internal corner, and 6m high above the top of the combustion chamber opening: [40] a much more realistic test of the fire performance of a cladding system than the previous small-scale surface spread of flame tests. The extent of damage caused to the external cladding system is evaluated, specifically the ability of the external cladding system to resist the propagation of the fire 2.5m upwards for at least 15 minutes. [41] Any falling debris and fire penetration from the external to internal face should also be assessed. [42]

BRE report (BR 135) Fire performance of external thermal insulation for walls of multi-storey buildings was revised in 2003 to incorporate the knowledge gained. BR 135 was revised again in 2013 to address new technologies in cladding and external wall systems and the publication of BS 8414-2.

#grenfelltower #uk

[trustME]

@piwniczak: mozesz jakies TLDR ?

[piwniczak]

@trustME: wedle przepisów taki pożar nie powinien zaistnieć :)

[trustME]

@piwniczak: wg przepisow w UK ludzie nie powinni nosic nozy, a ostatnio 3 takich nosilo i zarznelo 8 osob.

[piwniczak]

@trustME: :) generalnie jest to fragment studium przenoszenia się pożarów po zewnętrznych claddingach - czyli tak jak rzekomo przenosił się ten pożar. Od wczesnych lat 90tych wszystkie claddingi jednak powinny być zbudowane z całkowicie niepalnych materiałów