In recent years, insurers in Europe, for example in the United Kingdom, have increasingly been confronted by major damage due to fires where sandwich panels were evidently involved in the construction. As a result, these light buildings have come in for increased scrutiny from insurers.

  

Fig 7.8.1 The “Arena” administrative building with office and warehouses (Group – La Librairie - Electronic) in Libourne; France (1993), architect(s): Marigot office – M.O. Bâtiment, France – source [14]

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1. What are sandwich panels?

Sandwich panels or insulating sandwich panels are described in the following as multilayered components forming part of the construction and consisting essentially of two profiled metallic facings and an intermediate damp course.

Typical facings are produced from steel panels but aluminium panels are sometimes also used in practice. For this, the various properties of the materials at high temperatures, for example at critical temperature and melting point, determine how the components behave in the event of fire.

As insulators, both non-flammable materials (such as mineral compounds and fibreglass) and flammable materials (such as polyurethane/
polystyrene high-resistance foam (PUR/PS)) are used. Other constructional properties of insulators, for example heat protection and humidity protection, as well as flammability are important in the choice of insulators.

For the most part, sandwich panels are industrially pre-fabricated. Here, the non-positive connection between the layers is generally realised through adhesion, thus providing flexural and torsion rigidity for the components.

Sandwich panels can be connected in an airproof and waterproof manner with the corresponding edge and joint construction or fastened to substructures made of steel or wood. They are often used as components for roofs and outer walls, in particular for industrial, commercial and purpose-built constructions, for example cold stores and multi-purpose arenas, since constructions made of lightweight and pre-fabricated components can be completed quickly and economically.

The metallic surface of sandwich panels is also easy to clean, which, for example, is of great importance for food hygiene.

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Fig. 7.8.2 Example of a sandwich wall panel and the possible joint construction; source: [12]

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2. The current situation in Germany

Sandwich panels have been used in Germany as construction components for more than forty years now. Particularly when used as wall panels and non-supporting outer wall panels, sandwich panels with steel sheet facings with a core of non-flammable insulating materials can achieve the fire resistance classes according to DIN 4102; the thermal effects are fire tested during trials using the temperature time curve according to DIN 4102-2, which simulates a fully-fledged fire. Recognised systems are listed in, for example, the catalogue Baulicher Brandschutz; Produkte und Anlagen, Teil 3: Konstruktive Bauteile (VdS 2097-3) [Fire protection in construction; products and installations, Part 3: Construction components (VdS 2097-3)].

Sandwich panels with steel sheet facings and a core of PUR high-resistance foam without air film can be categorised under building class DIN 4102-B1 “Highly flammable” and are tested following the Brandschacht method according to DIN 4102-16. This test takes as its example an object on fire in a room, according to DIN 4102-1 (for example a wastepaper basket in the corner of a room) and is designed to have a duration of 10 minutes.

In particular in the case of coated and composite components that fire tests on a laboratory scale, however, only provide limited information on the fire performance of a built-in construction.

This is why major fire tests were conducted at the newly set-up Laboratorium für die Forschungs- und Materialprüfanstalt Badem-Württemberg (FMPA) in 1985. Here, there was testing of for example sandwich panels with 1 mm facings made of steel sheet that has been coated with acrylic resin lacquer and a core of PUR high-resistance foam without air film as a façade system.

The test was part of an extensive research programme for examining fire performance of steel and steel composite constructions, subsidised by the German Federal Ministry of Research and Technology (BMFT) and also followed critically by insurers and industry.

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Fig. 7.8.3 Major fire tests with FMPA and Brandschacht according to DIN 4102. Source: left [12], right MPA NRW

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In the following assessment, the fire performance of the façade system mentioned on page 7.8.3 was generally described as “surprisingly good” as the only burn-out was near the joints and, furthermore, burning of the steel sheeting and charring of the core of PUR high-resistance foam only occurred in the immediate vicinity of the fire impact. The system tested did not therefore contribute to either horizontal or vertical spreading of the fire. However, it is of note that during the fire test, there was quite a significant accumulation of smoke, which experience shows can endanger the safe rescue of personnel and effective fire-fighting in the building.

Sandwich panels when used as roofing components cannot generally achieve a fire resistance class according to DIN 4102. Nor can they fulfil the testing requirements of DIN 18234, which limits the spread of a fire in the area of the closed roof surface in the case of a roof with a large surface and an inclination of up to 20°, following an initial fire affecting the underside. Experience generally shows, however, that sandwich panels in the roof are hardly ever involved in initial fires breaking out.

Accordingly, industrially pre-fabricated sandwich panels with steel sheet facings and a core of PUR high-resistance foam without air film are generally given a positive assessment by insurers who with their many years of experience of damage normally prefer solid constructions. This is the case for example, in the VdS Guide 2000 Brandschutz im Betrieb [Fire protection in businesses] and in VdS 2216 Brandschutzmaßnahmen für Dächer; Merkblatt für die Planung und Ausführung [Fire protection measures for roofs; Leaflet for planning and execution].

The insurers’ experience of damage is for example documented in the Großschadenstatistik [statistics of major damage] regularly produced for, and supplied to, the business members of the Gesamtverband der Deutschen Versicherungswirtschaft e.V. (GDV) by this insurers’ association. Major damage in the context of industrial insurance involves a loss of at least EUR 511,292.

According to this, there has to date been no noticeable increase in major damage with a significant involvement of sandwich panels.

3. Damage in other European countries

There has been an ever growing number of cases of major fires in buildings with sandwich panels in European countries outside Germany, especially in the United Kingdom, with a particular concentration in UK businesses in the food processing sector, as clearly shown by the diagram below.

  

Fig. 7.8.4 Damage caused by fire in the food processing sector in the United Kingdom (in millions of GBP) according to the FPA (Fire Protection Association) – source: [13]

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Also other types of businesses, for example department stores and agriculture, are affected though. The Fire Protection Association (FPA) in the United Kingdom registered a total of 39 major fires, e.g. in the food processing sector, between 1992 and 1997; about half of these took place just in the two years 1996 and 1997.

This damage often led to losses running into tens of millions of pounds. In most of these cases, the insurance compensation due fell under the rubric total losses. The damage caused by two major fires in 2002 came to EUR 8 million and EUR 10 million.
There were some instances of physical injury that constructional fire prevention requirements should have prevented. Two fire-fighers were killed at a poultry processing plant in Hereford in the UK when the roof construction collapsed in a major fire in September 1993, and at a poultry processing plant in North Carolina in 1991, 25 out of 90 employees lost their lives and 54 were injured during a major fire.

3.1 The causes of damage

Analysis of this major damage showed that there was no direct link between the occurrence of the fire and the use of sandwich panels but instead the type of business played a role. A typical cause of fires was arson, which by the early 1990s was already recognised as a serious problem in most industrialised nations and was now being seen as the cause of more frequent fires in the food processing sector in the United Kingdom. Other typical causes involved, for example, the defective set-up of electrical installations and fittings or their insufficient maintenance.

Typical causes of fire in the food processing sector have their root, for example, in the fact that thermal processing procedures are used on a particularly large scale in food manufacture and processing. Together with working fluids such as grease and oil that are highly flammable and stored in relatively large quantities, the high operating temperature often leads to ignition.

Temperature limiters are indeed often required on thermal installations and fittings in order to manage the dangers of a fire breaking out; but these are often defective. Flammable packaging and refuse, large amounts of which can often accumulate in the food processing sector, can contribute significantly to the development and spread of a fire if, when organising the business, these thermal loads are not promptly removed or stored correctly.

 

Fig. 7.8.5 Major fire test with FMPA and Brandschacht, according to DIN 4102 – source: [13]

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Fig. 7.8.5 Major fire test with FMPA and Brandschacht, according to DIN 4102 – source: [13]

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Sandwich panels may no longer withstand thermal forces operating in the building if the thermal capacity at the time leads to an advanced or fully-fledged fire. Total damage is then often inevitable as the supporting constructions, which in the case of lightweight sandwich panels generally consist of steel, without additional protective construction measures such as the provision of a fire-resistant lining or coating or any other technical compensation such as an automatic fire extinguisher, fail very quickly.

If sandwich panels with a core of flammable insulating material are also to be used as part of an inner wall, as is possible in the United Kingdom, the flammable insulating materials may become locally accessible to the hostile fire by means of the wall bushing of operationally necessary leads provided in building and production or due to mechanical damage to the metal facings caused by a forklift truck for example. This can also contribute to the development and spread of the fire.

3.2. Testing practical use

Both insurers and other fire protection experts, in the United Kingdom for example, see the need to test and re-consider the practical use of sandwich panels due to the increasing tendency for major damage to occur. Operational experience by the Fire Service in the United Kingdom has shown, for example, that an advanced or fully-fledged hostile fire can in many cases penetrate deep into the sandwich panels and often cause the building or parts of it to collapse. The burning of flammable insulation materials can also often cause a considerable amount of smoke, making it significantly harder to fight the fire.

 

Fig. 7.8.6 Room corner test according to ISO 9705 – source: [13]

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Tests that have been carried out in this area independently but in parallel to each other, for example in the United Kingdom and Scandinavia, have shown that the fire performance of built-in sandwich panels can currently only be adequately assessed by major fire testing such as the natural fire testing carried out in Germany in 1985 or the room corner test according to ISO 9705. Further procedures for testing and classification have since been developed by, for example, the Loss Prevention Council (LPC) in the United Kingdom and Factory Mutual (FM) in the USA.

Major fire tests can on the one hand simulate the real effects that a fire can be expected to produce. In the room corner test according to ISO 9705, the output of the gas burner in creating the effect of the fire, reaches 100 kW for the first ten minutes and 300 kW for the second ten minutes. In comparison to this, the gas burner for the SBI test developed in the context of European harmonisation and which is shortly to replace the Brandschacht test according to DIN 4102-16, only produces an output of 30 kW for the entire duration of the test, which also lasts twenty minutes.

On the other hand, the test can be used on a scale of 1:1 to realistically examine the effects of the joint construction and the fastening of sandwich panels on its fire performance when built-in – in the harmonised European specifications also known as end use conditions. Experience shows that non-flammable metal facings cannot effectively prevent a fire from spreading just with sandwich panels with a core of flammable insulating materials.

The results of the above tests were published, for example, by the Building Research Establishment (BRE), on behalf of the Association of British Insurers (ABI), in the Report on verification of reaction to fire performance of sandwich panels used in the food industry. Also a few products and systems mainly using extruded/expanded polystyrene high-resistance foam (EPS/XPS) as a heat insulator were deemed unsuitable. Experience has shown that EPS and XPS can melt at temperatures as low as 150°C, leading, among other things, to the failure of the major link between the layer of heat insulation and the metallic facings that is necessary to ensure the stability of the sandwich panels. The BRE report, however, also advises against some other products and systems that use polyurethane high-resistance foam (PUR) as a heating insulation material.

3.3 The market situation

Insurers are now anticipating increasing damage in other European countries where similar sandwich panel systems with comparable facings have been used to the ones employed up to now in the United Kingdom.

The drastic growth in damage claims has led to very heated talks between the manufacturing industry and insurers that have among other things led to there hardly being any adequate cover available for properties with sandwich panels. In the United Kingdom, some properties are currently only covered by:

• A higher own risk on the part of the insured;
• Considerably higher insurance premiums than previously; and/or
• Fire protection measures to be fulfilled in the short term.

The fire protection measures include installing automatic fire extinguishers or the use of sandwich panels that are technically classed as unobjectionable, for example because they are fitted with a core of non-flammable insulating materials, and have to replace a number of existing constructions.

 

Fig. 7.8.7 A few headlines illustrating the consequences of increasing damage caused by fire – source: [13]

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4. The effects on Germany

The fact that Germany has until now not been affected by the costly trend in damage claims that has been seen in the United Kingdom is probably due to the following circumstances:

 

Fig. 7.8.8 Unprotected deep fat fryer following a fat fire and an example of a fire extinguishing system (extinguishing nozzle) – source: [13]

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Fig. 7.8.8 Unprotected deep fat fryer following a fat fire and an example of a fire extinguishing system (extinguishing nozzle) – source: [13]

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1. As early as the mid-1980s – partly due to the natural fire tests carried out at the FMPA – it was recognised by all those concerned that the design of the joints and the fixing of sandwich panels, of decisive importance for limiting the spread of fire and for assessing the fire performance of built-in sandwich panels, must also be borne in mind. A few material combinations that have been given a negative assessment in current tests, but are used none the less, for example in the United Kingdom, because of, among other things high cost pressure, are to be avoided wherever possible.
2. Commercial, industrial and purpose-built constructions are considered according to Construction law stipulations as buildings of a special nature or for a special purpose. As such and on the basis of Health and Safety legislation, they, together with their fittings, may have to fulfil stricter fire protection demands. Employers’ association Health and Safety insurance rules on working in kitchens (BGR 111), for example, state that deep fat fryers in facilities for the commercial preparation of hot meals and with a capacity of over 50 litres must be protected by suitable fire extinguishers or fittings.

3. For commercial and industrial properties in particular, insurers have long been recommending and promoting integrated fire protection concepts in which individual fire protection measures, for example:

• Dividing up fires by constructional separations;
• Installing automatic fire extinguishers;
• Appointing a Fire Protection Officer in the business/organisation; and
• Providing sufficient fire water

are specifically established for each property, mutually complement one another and are geared to one another according to risk and preventive objective.

It has been proven that precisely the operational fire protection organisation, including fire protection methods such as smoking bans, regular maintenance of safety installations and fittings and instructing the staff, can significantly reduce the dangers of a fire breaking out and spreading.

In order to prevent a similar trend in damage claims to that seen in the United Kingdom, information from current tests must be  considered accordingly during:

• Planning
• Constructive design of the joints and fitments as well as
• Assembly instructions

In this way, the proven practical use in Germany of products and systems for fire protection that are technically unobjectionable can be established and encouraged and fresh impulses initiated for future product and system development.

In order, for insurance purposes, to facilitate assessment that is appropriate for the level of risk, the various systems of sandwich panels that can obviously demonstrate very different fire performance and must therefore be classified according to recognised technological rules, also need to be clearly identified when installed in order to be able to ascertain which type of sandwich panels were used in the respective property. For this, one practice that has proven its worth on the ground is the required labelling of construction products according to the general construction approval.

  

Fig. 7.8.9 Basic formation of an integrated fire protection concept – source: [13]

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5. Summary and perspective

Over recent years, there has been, in European countries outside Germany, an ever larger number of instances of major damage following fires with the significant involvement of sandwich panels. In the United Kingdom, for example, this has been the case particularly in the food processing sector, but agricultural businesses and department stores have also been affected. The cause of the fires bringing about this damage – as for example, can be seen from the insurers’ statistics – has also been established in the case of other damage caused by fire without the involvement of sandwich panels. There are, for example, cases of arson and defective electrical installations.

If an initial fire is not discovered and effectively tackled on time, for example outside working hours, experience has shown it can easily become a fully-fledged and full-blown fire if there is no automatic fire extinguishing system. In this way, the hostile fire may not just find plenty of fuel at the operationally present thermal load but may in many cases also penetrate the sandwich panels and, in case of failure of the supporting construction, lead to total damage. The involvement of flammable heating insulation in sandwich panels in a fire breaking out also makes tackling such a fire harder due to the substantial accumulation of smoke. If the equipment and the building capacity are especially sensitive to smoke, as for example is the case due to stricter hygiene demands in the food processing sector, a lot of material damage is to be expected, even if the building does not collapse.

In principle and in practice, it has been demonstrated that the dangers of a fire breaking out and spreading can be effectively limited by integrated fire protection concepts. In the context of this fire protection concept, fire protection measures of a constructional, technical, organisational and protective nature are integrated and implemented. Guidance for this can, for example, be taken from the Guide VdS 2000 “Brandschutz im Betrieb” [Fire protection in businesses].

 

Fig. 7.8.10 Diagrammatic course of a full-blown fire – source: [14]

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The involvement of sandwich panels in an increasing number of major cases of damage in Europe, for example in the United Kingdom, has its justification in its construction and use.

In order for the fire performance of built-in sandwich panels to be assessed realistically, fire tests to the scale of 1:1 must also be used in many cases, as in some cases this is the only way the effects of the construction of sandwich panels on the fire performance can be properly ascertained.

The natural fire testing that took place in Germany in the 1980s and current tests in other European countries have confirmed this. The fire performance of sandwich panels can, as experience has shown, be affected in particular by the choice of material for the heat insulation layer and metallic facings, the edge and joint construction and the fastening.
Germany has until now been unaffected by the costly trend in damage claims that has been seen in the United Kingdom; nevertheless, insurers in Germany will, on the one hand continue to attentively follow and carefully assess trends in damage claims at home and abroad and, on the other hand, the development, testing and classification and use of sandwich panel products and systems so that, if necessary, they can make an appropriate response and take early action in this regard.

The fact that damage prevention is more effective than compensation has been shown by the example of sandwich panels being used as roof and wall panels.

 

Abb. 7.8.11 - Quelle: [14]

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Fig. 7.8.11 – source: [14]

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Fig. 7.8.13 – source: [14]

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Figures 7.8.11 to 7.8.13 show the course of an SBI test for the technical classification for fire protection purposes of sandwich panels (B1 - high-resistance foam B2) on 4 February 2000 at MFPA Leipzig. The sandwich panels do not contribute to the maintenance of the fire. The fire goes out on removal of the source of the flame