Composite sandwich panels can be extremely cost effective in the construction of new buildings, but have all the ‘old’ problems gone away, or are there new problems around the corner? Bill Parlour looks ahead.
Over a period of about ten years from 1993, many fire brigades and insurance companies witnessed large fire losses involving sandwich panels. The ‘problems of fire’ in relation to poorly selected composite sandwich panels had well and truly arrived
Finally in the new millenium, partly because of the potential of very widespread damage from fires in some buildings using sandwich panels with combistible cores – and the threats to firefighters and occupants alike – the government published guidance as a new Appendix F in Approved Document B in 2000. Interestingly, the guidance provided was limited to sandwich panels when used internally in buildings, and seemed to stand aside from panels used as external cladding to buildings. The guidance highlighted:
– The fire behaviour of core materials and fixing systems
– Firefighting problems
– Design recommendations
– Appropriate core choice for named uses
At much the same time, insurers were also readdressing these issues and the result finally emerged as repositioned Loss Prevention Standards LPS 1181 Parts 1 and 2 respectively for panels used externally or internally.
Reaction-to-fire
Let’s consider the insurer’s LPS tests. As far as reaction to fire is concerned, both types of panels – for external and internal use – are tested using the long established Wall and Ceiling Lining test arrangement. Simply stated, this is a 10m long room, 4.5m wide by 3m high with a 0.75m downstand at the open end. An adjustable window in one wall near the ‘hot end’ allows ventilation to the fire source.
In the case of external panels, the room is formed by panels fixed to a steel frame. External panels have complex 3D jointing systems, with and without cover strips. For internal panels, the room is formed by free-standing panels fixed to each other and ceiling supported from a suitable framework, so the support is quite different. These panels have simple butt jointed edge to edge construction, but are usually retained in channels at top and bottom edges.
Usually, the LPS 1181 fire source is from a burning timber crib, raised off the floor adjacent to the corner of the far end panels. The crib design is critical as it effects the rate of burn. After the cooling down of the test and within 24 hours, the extent of the damage to internal and external panel facings is assessed; the internal facing is removed to check damage within the panel and the depth of char of the internal insulation is measured. If the results fall within set reference limits, the panel system as tested gains EXT-B status for reaction-to-fire testing, but fire resistance testing also needs to be acrried out. Note that assuming a successful test result, sandwich panels tested with long side edges horizontally can be used in a vertical condition as well, but if tested with the long side edge in the vertical orientation, then it cannot be assumed as suitable for horizontal use as well.
Importantly too, if tests are made with different combinations of insulation to wall and roof panels, then the results are limited to those combinations as tested. So, for example, if the test is made with foam core to the walls and mineral wool core to roof, the test results are not applicable to panels with foam cores to walls and roof! Test data is also limited to the panel thickness, as tested, or a lower thickness.
When panels are intended to be used internally within buildings, LPS 1181 Part 2 has an additional requirement beyond LPS 1181 Part 1. For 60 minute INT-1 classification, the severity of the fire source is increased and a propane gas burner is used instead of a timber crib. The gas burner peaks at 1000KW fire exposure and is held at 600KW until 30 minutes have elapsed. Compare this to the timber crib which reduces to about 150KW after 10 minutes or so. The timber crib is used for external panels and also for internal panels to meet the less severe 30 minute INT-2 and INT-3 classifications for reaction to fire testing. Note that the 60 minute and 30 minute durations originate from separate resistance-to-fire testing, as indicated in the table.
Resistance-to-fire
As mentioned, sandwich panels can only be classified as Grades EXT-A60, A30 or A15 and INT -1 or INT-2 if fire resistance testing to LPS 1208 [BS 476 Part 21] is also carried out. Note that 27 minutes insulation is deemed acceptable for EXT A-30 panels.
EXT A-15 is deemed acceptable by LPS 1181-1 for external sandwich panels that are not within the unprotected are, as defined in Approved Document B, but in the ‘protected zone’ on either side of a compartment wall, the fire resistance needs to be higher, as indicated in the table. This is in contrast to sandwich panels used for internal divisions of space in buildings, where fire resistance performance has to be demonstrated for 60 or 30 minutes’ integrity and insulation for INT-1 and INT-2 grades respectively. So it’s tougher to satisfy insurers for panels used inside buildings!
Of course, we cannot test everything since the cost would be prohibitive. So we test agreed arrangements and apply rules for extending the test data to ‘extended’ fields of application. This is where new concerns start to appear.
LPS 1181 Part 2 and LPS 1181 both contain rules for ‘field of aplication of test results’. In the case of external panels, these rules relate to product type, thickness, height, orientation, depth of profile and so on, whereas for internal panels similar rules exist, but additional ones also appear for criteria such as unsupported span of ceilings and support distances of fire resisting panels.
Standards muddle
The European product standard EN 14509: 2006 (Roof covering products for discontinuous laying and products for wall cladding) has now been released by CEN TC 128 but has not yet been included in the EU’s Official Journal, and therefore remains ‘unofficial’ at the time of writing. Disagreement continues over the rules for the field of application of test results contained in the document, since some rules are included in the product standard which have not been agreed by CEN TC 127, the over-arching European technical committee concerned with all aspects of fire safety. To help clarify the primacy for ownership of such rules, the CEN programme manager sent a letter to the various technical committees clarifying that primacy lies with CEN TC 127, an extract of which appears in the panel on this page.
Since contradictory positions still exist between the CEN TC 127 Fire Committee and writers of the product standard in CEN TC 128, where does this leave the situation?
The plenary meeting of CEN TC 127 recently held in Prague on 11 October has recommended formal meetings between CEN management and the two committees which drafted the text of EN 14509. CEN TC 127 have agreed that an explanation letter for ‘exception’ – effectively blocking the existing product standard route for CE marking – will be drafted for issue by TC 127. It is therefore entirely possible that Notified Bodies may give priority to the TC 127 documents over and above the non-released product standard EN 14509 draft from TC128, in all determinations of the classification for composite sandwich panels under CE marking procedure.
So the publication of EN 14509 ahead of CEN TC 127’s concerns may be a recipe for chaos ahead. It strongly suggests that existing rules for the application of test results as presently contained in EN 14509 ‘Self supporting double skin metal faced insulating panels – Factory made products – Specifications’ will be changed sooner or later.
It should be pointed out that the Extended Rules in EN 14509, appearing as direct rules, also go further than the permitted limits in insurers’ standards LPS 1181 Parts 1 and 2, so it would be very prudent to accept insurers’ conclusions in the interim period.
UK position
The following summarises the issues to take into account relating to recent changes to UK fire law when considering composite panels:
– The Fire safety Order 2005 places a duty on responsible persons to make a fire risk assessment
– The CDM Regulations 2007 build on existing law to ensure that clients know what they are getting – essentially they should not be misled.
– Approved Document B 2006. Regardless of Appendix F introduced in 2000, readers should familiarise themselves with the new regulation 16B in Approved Document B Appendix G. This refers to a new duty such that fire safety information shall be given to the ‘responsible person’ at the completion of a project, or when the building or extension is first occupied. Fire safety information means information relating to the design and construction of the building – including all assumptions made in the design of the fire safety arrangements.
Insurers have previously published their Essential Principles document – a short overview of ‘must do’ actions. Principle 1 of 10 includes “compliance will be deemed to have been satisfied if if the products used are non-combustible; Euroclass A1 or A2, or are pproved by LPCB to the appropriate part of LPS 1181”.
I have outlined some of the key factors above.
In summary, correct panel selection is just as important now as before. You should also ensure that the field of application is fully appreciated, as documented, and check the details in the test reports of the fixings required for claimed resistance to fire performance. This is vital for panels in the ‘protected zone’ either side of all compartment walls in buildings where they meet the cladding and roof. Finally, make sure that your insurer agrees with your conclusions!
Bill Parlor is technical officer for the Association for Specilaist Fire Protection (ASFP) and has been a CEN national on reaction-to-fire.
PRIMACY LIES WITH CEN TC 127
A letter from the CEN Programme Manager
“At the CEN/TC 127 Fire safety in buildings plenary meeting held on the 30th October 2006, the issue on the TC responsibility for drafting standards related to fire was raised by some of the participants. It is understood that some product Technical Committees are involved in drafting standards on reaction/resistance to fire, which is within the scope of CEN/TC 127 alone. CEN/TC is responsible for drafting standards on reaction/resistance to fire linked to all the construction products and it is supposed to have the expertise to draft them.
This issue was already discussed several years ago and the situation has not changed. At the meeting [on] 30 October I made it clear that CEN/TC 127 has the mandate for drafting all reaction-to-fire and fire resistance test standards. This includes test methods and Extended Application standards (EXAPs). Therefore, CEN/TC 127 has primacy over all other TCs.
However, if there are areas in which CEN/TC 127 does not have the expertise or is not currently involved with the preparation of the required standards, or does not have the required resources, then other CEN Technical Committees could take the lead, but they should make CEN/TC 127 aware of their needs in the first instance. I take this opportunity to ask the CEN Technical Committees drafting construction product standards to establish close liaisons with CEN/TC 127 to support its work.
This issue was already discussed several years ago and the situation has not changed. At the meeting [on] 30 October I made it clear that CEN/TC 127 has the mandate for drafting all reaction-to-fire and fire resistance test standards. This includes test methods and Extended Application standards (EXAPs). Therefore, CEN/TC 127 has primacy over all other TCs.
However, if there are areas in which CEN/TC 127 does not have the expertise or is not currently involved with the preparation of the required standards, or does not have the required resources, then other CEN Technical Committees could take the lead, but they should make CEN/TC 127 aware of their needs in the first instance. I take this opportunity to ask the CEN Technical Committees drafting construction product standards to establish close liaisons with CEN/TC 127 to support its work.”
