Cladding Remediation Programme: Single Building Assessment specification

Appendix F. Fire Performance Risk Factors

The following images show Table K.1 of the PAS 9980 document which covers fire performance risk factors. It gives a non-exhaustive list of examples of common factors influencing the likely speed and extent of fire spread, based on the properties and fire performance of the materials, components, systems and configurations of the building’s EWS.

Note that no single row in Table K.1 of the PAS 9980 gives a definitive answer on risk. Where an entry is considered, positive, negative or neutral is purely indicative of the potential influence it might have. A competent assessor will use their judgement when using the table to determine the actual relevance of each factor and its significance in the context of the particular building under consideration. Where numerical values are given they are only intended to be indicative as to the possible influence the particular factor might have in a risk-based assessment.

Where a risk factor is marked with an asterisk (*), this indicates that it is notably more of a positive influence.

Figure D.1 – Table K.1 of PAS 9980 – Fire performance risk factors

Where a risk factor is marked with an asterisk (*), this indicates that it is notably more of a positive influence.

K.1 General

Note 1 Calorific values are to be based on BS EN ISO 1716 test results.

Note 2 This is a broad indicator only and needs to be seen in the context of the particular component to which it relates, how that component interacts with other materials, the quantity of the material, its location and the extent to which it covers the building. The boundaries between the different ranges need not be seen as rigid in this context. Depending upon this, judgement made by the external wall assessor may allow differences, e.g. up to 6 MJ/kg as still positive or over 20 MJ/kg as negative. It is likely that more in‑depth technical assessment would be needed to fully utilize the values for individual components and their contribution to the wall build‑up as a whole.

Positive

Materials with a calorific value (gross heat of combustion) of ≤3 MJ/kg

Neutral

Materials with a calorific value (gross heat of combustion) >3 MJ/kg and ≤35 MJ/kg

Negative

Materials with a calorific value (gross heat of combustion) of >35 MJ/kg

Positive

External wall materials, components/systems and configurations that are combustible, but known to provide adequate fire performance in certain circumstances

[Based on knowledge of fire behaviour from fire tests. For example:

• any combination or system which has been classified to BR 135 [15] for same build‑up, albeit not an exact match; or
• any combination or system which has passed an alternative large‑scale test (e.g. LPS 1181, Part 1 [33]).]

Note 3 Care needs to be taken when considering the weight that can be attached to tested build‑ups that differ from the actual wall build‑up on the building. The performance of build-ups in a test only provides an indication of potential performance; it cannot be assumed that the same performance will be always achieved.

Note 4 BS 9414 has, since its publication, been used in relation to this aspect of assessment; however, it is not intended as a means of reverse engineering an applicable BS 8414 test based upon site observations (see Clause 11).

Neutral

External wall materials, components/systems and configurations that are combustible, but with the potential to provide adequate fire performance in certain circumstances

[Knowledge of fire behaviour from only limited fire tests. For example:

• subject to intermediate‑scale tests (e.g. ISO 13785‑1, NFPA 285) and/or ad‑hoc fire tests, but not large‑scale tests; or
• components classified to BS EN 13501‑1 but not complete system/configuration.]

Negative

External wall materials, components/systems and configurations that are combustible, but with no knowledge of fire behaviour

[No evidence available from fire testing. For example:

• not tested in large‑scale or intermediate‑scale fire tests (e.g. BS 8414);
• not classified to BS EN 13501‑1; or
• no ad‑hoc testing.]

K.2 External surfaces: reaction to fire classes

Note This is a broad indicator only, and needs to be seen in the context of the particular component to which it relates and where it is within the wall build‑up. It is likely that more in‑depth technical assessment would be needed to fully utilize the values for individual components and their contribution to the wall build‑up as a whole.

Positive

Class A1/A2*, Class B

Neutral

Class C

Negative

Class D, Class E, Class F

K.3 Facings/cladding panels

Note Heat release rate (HRR) is an important indicator of performance, given that it indicates how rapidly heat energy is released in the process of combustion. It is not currently possible to state values here, but studies that compare the HRR of different materials, components and systems in similar conditions can be useful references to enable this factor to be considered.

Positive

Low HRR

Neutral

-

Negative

High HRR

Positive

Mechanically fixed

Neutral

-

Negative

Adhesive fixed

Positive

Solid metal panels with high melting point (>800 °C)

(Typically, steel)

Note Some paint finishes can result in a Class B or lower rating.

Neutral

Solid metal panels with low melting point (<800 °C)

(Typically, aluminium, zinc and copper)

Negative

Metal faced panels with a combustible backing

(Typically, aluminium on plywood)

Positive

Category 1 ACM or other MCM

(At least Class A2)

Neutral

Category 2 ACM or other MCM

(Typically, a combustion modified polyethylene core, also referred to as FR type)

Negative

Category 3 ACM or other MCM

(Typically, an unmodified polyethylene core)

Positive

Other rigid non‑combustible facings

(Typically:

• brick;
• ceramic;
• stone;
• clay tile;
• concrete;
• stone wool cladding boards; and
• cement fibre boards)

Masonry or concrete at least 75 mm thick*

Neutral

Brick slip with organic mortar

Brick slip with inorganic mortar*

Negative

Brick slip and other similar facing/ cladding panels supported by thermoplastic materials

Positive

Glazing and glazed curtain walling (See K.11 for infill panels)

Note 1 Glass type might not be Class A2 or better, but still considered positive.

Note 2 Based on past experience of laminated glass in fires, replacement of laminated glass is not, at the present time, considered justified in relation to existing blocks of flats.

Note 3 Further consideration of laminated glass is given in Annex L.

Neutral

-

Negative

-

Positive

Glass rainscreen panels, where either:

• at least Class A2; or
• if incorporating organic resins, binders, etc., a similar combination has been subject to BR 135 classification

Neutral

Glass rainscreen panels, with organic resins, binders, etc.

Negative

-

Positive

HPL, combustion modified (no lower than Class B), when used in combination with non‑combustible insulation

Note Class B products are sometimes also referred to as an “FR” HPL.

Neutral

HPL (Class C or lower), when used in combination with non‑combustible insulation*

Note 1 Class C or lower products are sometimes also referred to as a “standard” HPL.

HPL, combustion modified (no lower than Class B), when used in combination with combustion modified polymeric foam insulation

Note 2 Class B products are sometimes also referred to as an “FR” HPL.

Negative

HPL, combustion modified (no lower than Class B), when used in combination with polymeric insulation*

Note 1 Class B products are sometimes also referred to as an “FR” HPL.

HPL (Class C or lower), when used in combination with polymeric foam insulation

Note 2 Class C or lower products are sometimes also referred to as a “standard” HPL.

Positive

-

Neutral

Timber, direct on non‑combustible substrate*

Timber, in combination with non‑combustible insulation

Negative

Timber, in combination with combustible insulation, etc.

Positive

-

Neutral

Other combustible facing or panel with combustible content, but not readily ignitable (at least Class B)

Negative

Other combustible facing or panel with combustible content (Class C or lower)

K.4 Panel construction

Note 1 Gap sizes can be highly influential in terms of performance of in large‑scale tests and the values given above are only intended to be indicative of their possible influence as a factor in a risk‑based assessment. Panels can take different forms: flat sheets and cassettes. Different methods of fixing are possible including hook on, rivet fixed and adhesive bonded. These variations can result in differences in fire performance in certain fire tests. Further commentary on this is given in Annex L.

Note 2 Gaps might result from loss of integrity of sealant during fire exposure.

Positive

No gaps between panels

Neutral

Limited size of gaps between panels

(Typically <10 mm)

Negative

Gaps between panels of 10 mm to 20 mm*

Gaps between panels of >20 mm

K.5 Cavities

Note The minimum fire resistance for a cavity barrier/stop is 30 min integrity/15 min insulation. Proprietary products are made for this purpose, but suitable protection will be provided if the following are present:

• steel at least 0.5 mm thick;
• timber at least 38 mm thick;
• polythene‑sleeved mineral wool, or mineral wool slab, installed under compression in the cavity; or
• calcium silicate, cement‑based or gypsum‑based boards at least 12 mm thick.

Fire stopping that is present to close gaps in compartmentation provides a higher standard of fire resistance than a cavity barrier/stop.

Positive

Facings into the cavity at least Class A2

Neutral

Facings into the cavity combustible, but at least Class B

Negative

Facings into the cavity combustible, but Class C or lower

Positive

Cavities closed by barriers/fire stopping located in line with all of the following:

• compartment floors;
• compartment walls;
• around openings, e.g. windows, doors; and
• ventilation ducts, grilles and other openings for services

Note Suitable protection for ventilation ducts, grilles or other openings for services could take other forms, e.g. intumescent collars where passing through the walls, steel sleeves around the ducts and duct extensions to the cladding panels.

Neutral

Cavity barriers present with no more than minor workmanship defects

Negative

Cavities closed at least at compartment floors and walls but not:

• around windows and other openings*; or
• at ventilation ducts, grilles or other openings for services*

No cavity barriers present, or cavity barriers ineffective through poor installation/maintenance

K.6 Insulation

Note This is a broad indicator only. It is likely that more in‑depth technical assessment would be needed to fully utilize the values within the context of the particular wall build‑up.

Positive

No insulation

Neutral

-

Negative

-

Positive

Class A1/A2, Class B

Neutral

Class C

Negative

Class D, Class E, Class F

Positive

Mineral/glass insulation

Neutral

Thermoset polymeric foams that form a stable char on fire exposure, e.g. phenolic foams and some PIR foams

Note Consideration of the thickness of such insulation cannot be taken into account here, but is highly relevant in a more in‑depth technical assessment when considering the contribution of the burning insulation to the heat generated in the fire and heat transfer to the rest of the wall build‑up.

Negative

Thermoplastics (e.g. EPS/XPS) or thermoset polymeric foams that do not form a stable char on fire exposure (e.g. PUR)

Note Consideration of the thickness of such insulation cannot be taken into account here, but is highly relevant in a more in‑depth technical assessment when considering the contribution of the burning insulation to the heat generated in the fire and heat transfer to the rest of the wall build‑up.

K.7 Substrate

Positive

Masonry, >75 mm thick*

Masonry, <75 mm thick

SFS with cement, calcium silicate or magnesium oxide-based sheathing of Class B or better and non‑combustible (Class A1/A2) insulation

Neutral

SFS with sheathing of Class B or better and combustible insulation

Timber frame, CLT, SIPs, etc., with sheathing of Class B or better and non‑combustible insulation

Negative

Timber frame, CLT, SIPs, SFS, etc., with OSB or similar sheathing and combustible insulation

K.8 Sheathing boards

Positive

Class A1/A2

Cement, calcium silicate or magnesium oxide-based Class B

Neutral

Other Class B

Class C

Negative

Class D, Class E, Class F

OSB, hardboard or similar

K.9 Insulated core panels

Positive

Combustible insulation, but panels either:

• classified to BR 135 [15]; or
• met success criteria in alternative large‑scale fire testing (e.g. LPS 1181, Part 1 [33] and LPS 1208 [34]) Non-combustible insulation encapsulated in metal

Neutral

Readily combustible insulation, but fully encapsulated in steel

Negative

Readily combustible insulation, but not fully encapsulated

Readily combustible insulation, but only encapsulated in aluminium or other low melting point metal

K.10 ETICS

Note The fire performance of ETICS is a specialist area requiring external wall assessors to have relevant expertise. ETICS with specifically formulated renders can achieve classification to BR 135 [15] even with polymeric foam insulation. However, in‑depth technical assessment might be necessary where there is reliance on information suggesting that the ETICS on the building is one classified to BR 135 [15] and intrusive inspection has revealed potential installation issues, for example, that could be critical to performance in the particular application.

Positive

Thin organic render or inorganic render on Class A1/A2 insulation

Neutral

Inorganic render on thermoset polymeric foams that form a stable char on fire exposure, e.g. phenolic foams and some PIR foams

Thick inorganic render on thermoplastic polymeric foams (e.g. EPS/XPS)

Thermoset polymeric foams that do not form a stable char on fire exposure (e.g. PUR) with fire breaks through the full depth of the insulation at each floor level

Negative

Any other render system

K.11 Infill/spandrel panels

Positive

Glazed (excluding vision glazing), with Class A1/A2 core

Metal faced, with Class A1/A2 core

Thermoset polymeric foams that form a stable under fire exposure (e.g. phenolic and some PIRs) encapsulated with steel

Neutral

Thermoset polymeric foams that form a stable char under fire exposure (e.g. phenolic and some PIRs) faced on front and rear with Class A1/A2 materials (this could include laminated glass on the front face)

Other polymeric foams fully encapsulated with steel

Note Consideration of the thickness and sizes of such panels cannot be taken into account here, but is highly relevant in a more in‑depth technical assessment when considering the contribution of burning panels to the heat generated in the fire and heat transfer to the rest of the wall build‑up.

Negative

Panels with either combustible facing materials and/or thermoplastic cores not fully encapsulated by steel

Note Consideration of the thickness and sizes of such panels cannot be taken into account here, but is highly relevant in a more in‑depth technical assessment when considering the contribution of burning panels to the heat generated in the fire and heat transfer to the rest of the wall build‑up.

K.12 Internal finishes

Note It is not anticipated that internal finishes of external walls would be a notable risk factor, especially if they comprise a paint or wallpaper finish. However, it is possible that there might be finishes that, in the context of the overall wall build up, might influence fire spread to the extent that they constitute a negative risk factor and would need to be considered.

Positive

-

Neutral

-

Negative

-