European approach to assess the fire performance of façades

Several attempts have been made in the past to develop a European harmonized testing and assessment method for façades before the European commission decided to publish a call for tender on the topic. A project consortium from five countries (Sweden, UK, France, Germany and Hungary) applied to the call for tender and was contracted to develop a European approach to assess the fire performance of façades. 24 sub‐contractors and 14 stakeholder entities were part of the project. The objective of the European project was to address a request from the Standing Committee of Construction (SCC) to provide EC Member States regulators with a means to regulate the fire performance of façade systems based on a European approach agreed by SCC. The initial stages of this project were focused on establishing a register of the regulatory requirements in all Member States in relation to the fire performance of façade systems, and to identify those Member States who have regulatory requirements for the fire performance façade systems which go beyond the current EN 13501 (reaction to fire and fire resistance) classification systems and to collate the details of these additional requirements. After having confirmed the regulatory needs a testing and classification methodology based on BS 8414 and DIN 4102‐20 was developed to address the identified key performance and classification characteristics. This paper is a short overview of results the two‐year development work, which Final Report published by the European Commission in 2018.

to publish a call for tender on the topic. A project consortium from five countries (Sweden, UK, France, Germany and Hungary) applied to the call for tender and was

| INTRODUCTION
As identified by the Invitation To Tender (ITT), the primary objective of this project is to develop a common method to allow the assessment of the fire performance of façade systems. The assessment is a full-scale assessment of façades to catch effects of details such as mounting, fixing, air gaps, lengths, singularities and weak points such as windows. In this context, assessment based only on reaction to fire and/or fire resistance provisions is not necessarily enough. 1,2 The initial stages of this project were focused on: • establishing a register of the regulatory requirements in all Member States in relation to the fire performance of façade systems, and • to identify those Member States who have regulatory requirements for the fire performance façade systems which go beyond the current EN 13501 (reaction to fire and fire resistance) classification systems and to collate the details of these additional requirements. 3 After having confirmed the regulatory needs the following steps were discussed: • a testing and classification methodology based on BS 8414-Fire performance of external cladding systems series and DIN 4102-20-Fire behaviour of building materials and building components-Part 20: Complementary verification for the assessment of the fire behaviour of external wall claddings to address the identified key performance and classification characteristics. 4,5 • a verification and validation proposal, in the form of a round robin programme to support the development of the proposed testing and classification methodologies.
• an Alternative assessment method which was developed on the basis of the comments from stakeholders during the project Several hundreds of comments were received during the project and were implemented in the development.
The results of the workshops and seminars on the topic which have been held within Europe in the past 10 years, identify that the most difficult and important part of the task is the definition of a classification system which is acceptable by all Member States accounting for their national regulations and meeting the requirements of the Construction Products Regulation (CPR). 6 The classification system should be transparent and should fit within the framework of existing national regulations, and should be as simple as possible, for example, using the minimum number of classes required to enable Member States to effectively maintain their required safety levels. It has also been identified that the assessment method should be applicable to the wide range of façades systems available in the market including glazed façades, green façades and other emerging technologies.
Both the work from the EOTA PT4 façade testing task group and an EGOLF workshop held in October 2015 sought to collect data and experience on the current national regulations and test methodologies used in Europe. Both activities generated outlines for the development of possible classification systems and this experience has been used as part of this project. Key areas missing from the earlier studies included: -The consideration of a façade kit as a construction product.
-The consideration of a façade as a part of a specific building. In some national regulations this would mean that detailing such as window openings may also need to be considered.
-How to manage direct applications and extended applications including whether the performance of the façade system can be based on the fire characteristics of single components within the façade system.
-Fire scenario identification for each of the Member States that regulate for the fire performance of the façade system based on alternative assessment methods.
Both, the Proposed and the Alternative assessment method have been developed from the data collected during the project and the findings from the associated workshops and meetings presented in this report. The methodology and associated findings provide the basis on which the tasks outlined in the ITT have been addressed.
These approaches are also designed to enable regulators to review local building regulation requirements to ensure required safety levels can be maintained and allow industry to have a clear understanding the scenarios and classification methods proposed for determining the classification of fire performance for façade systems.
This paper is a short overview of results of the two-year development work, which Final Report was published by the European Commission in 2018. 7 2 | LIMITATIONS It has not been possible to include measurements for all characteristics identified as part of the initial regulatory survey. The proposed assessment methods were developed to produce working assessment methodologies that can be presented to the European standards making body (CEN) as baseline documents for potential development into a European method for the assessment of the fire performance of façades.
The baseline test methods were defined in the ITT as the BS 8414 series and DIN 4102-20 protocols. It was therefore decided to investigate the differences between the prescribed methods and the other test methods used in the Member States, and to define whether any changes were required to the predefined methods to fulfil the requirements of the regulations in the Member States. Examples of modifications to the predefined methods included variations to the size of the test assembly, inclusion of a secondary opening, junction detailing between façade and floor and some performance criteria.
It has not been possible to find published comparable information on the key performance characteristics such as heat exposure to the test specimen for all the currently available test methods, so it has not been possible to undertake any comparisons on these key parameters between the proposed methods with other test methods currently

| REGISTER OF REGULATORY PROVISIONS
At the request of the SCC the project was established to provide a proposed European harmonized approach to the fire performance assessment and classification for façade systems. In order to ensure a clearly The respondent was asked whether this definition adequately covered any national definition according to their building regulations.
If it did not, they were asked to provide a suitable definition according to their national regulations.
The results show that the term façade is only rarely used in the regulations. More frequently are the terms "external wall", "cladding", or similar used. The proposed definition, with some fine tuning, was acceptable for most countries: of 24 countries 12 countries answered with "yes"-this working definition is in accordance to their national system, four answered that this definition suits their national systemeven if it is not implemented yet. Swiss, German and Austrian regulations distinguish between the exterior wall and the cladding for which different requirements exist. The Swedish regulations refer to the exterior wall. The Belgian regulations refer to external wall construction of any type or constitution without any loadbearing function.
All countries have regulations and/or guidance governing the fire performance of façades. These regulations are mainly covered by the existing European system on reaction to fire and fire resistance.
Fourteen countries stated that they have additional requirements that are not covered by the EN 13501-1 reaction to fire and/or EN 13501-2 fire resistance classification system. For some countries it is clearly stated that a specific test method shall be used but for other countries the regulation enables the use of performance based testing at medium or large scale to demonstrate performance against the requirements of the regulations.
A total of 12 different test methods have been identified as being either currently in use, or referenced in the regulations, throughout Europe. The different test methods, and the countries using them, are presented in Table 1.
During the final drafting stages of the project report, information was received from Italy in relation to a recently finalized national fire performance assessment method for façades. Therefore, it has not been fully assessed within the scope of this project.

| COMPLEMENTARY VERIFICATIONS
As part of the regulatory survey the group also sort to identify any verification or assessment which are recorded in the register (and thus a part of the regulatory needs of the EU/EFTA Member States).
All participating countries have been asked during the inquiry whether they have additional requirements for the fire performance of façades which are not covered by the already harmonized methods according to EN 13501-1 and 2. 14 of 24 European countries answered that they have additional requirements. The main purposes of these requirements are: -Limitation of fire spread on the surface and inside the façade system -Demonstration of fire performance for systems which do not follow or cannot meet the fire performance characteristics for individual components, for example, insulation which does not fulfil required reaction-to-fire class Test methods used in Europe and countries using them [8][9][10][11][12][13][14][15][16]   Therefore, it is important to compare temperature and heat flux levels in the different test methods to assess the severity of the tests and this will be investigated further as part of the round robin testing and will assist regulators in assessing the appropriate levels of performance between current and proposed methodologies.
Information on heat exposures to the test specimen of all methods used has been asked for, but very limited information has been obtained. Since very little information has been obtained on the heat exposure to the specimen, and the available information has been measured differently, it is not possible to compare the different methods.

| FALLING PARTS
As identified in the survey Some Member States have requirements for falling parts and burning debris/droplets to be assessed. These requirements appear to reflect two safety goals: -The protection of escape routes and the rescue services.
-The prevention of secondary fire arising from burning debris/ droplets.
The robustness of façade systems with respect to falling off and burning debris/droplets is also required in some countries. The national requirements are defined differently, in some cases directly in the regulations and in other it is specified in the test methods. The requirements are also specified differently from very specific measurable quantities to quite loosely defined outputs such as "no large pieces shall fall down". The requirements used in Europe are summarized in Table 2.
The requirements can be grouped into three main categories, criterion related to weight, area or requirement not expressed with measurements. The falling pieces are difficult to measure during (or after) test due to the time factor and damage of falling pieces. A time independent solution is needed which provides evaluation method of falling pieces before the large pieces reach the ground. -Only one other method that uses a wing and that wing is considerably larger.

| COMPARATIVE ANALYSIS
-Four methods have windows or secondary openings included in the test rig, LEPIR 2, MSZ 14800-6, SP Fire 105 and Engineering guidance 16.
-LEPIR 2 and MSZ 14800-6 are using compartments on two levels Table 3  In the SP Fire 105 method heptane is used as fuel which in the configuration used gives a very rapid temperature increase compared to that of wood cribs. The maximum heat release is of the same magnitude as the other large scale tests, but the duration is shorter. It should also be noted that the smoke density is different depending on the fuel, while gas burners generally gives a cleaner smoke heptane produces a heavy black smoke. The smoke radiates heat to the specimen so depending on the type of smoke the heat exposure to the test specimen may be different.  Only to be observed and not assessed.

T A B L E 2 National requirements on falling off and burning debris/droplets
Another factor that may affect the heat exposure to the test specimen is the geometry and the ventilation conditions of the combustion chamber.

| SECONDARY OPENING
In some national test methods are details such as windows or detailing around window openings included and assessed. It is therefore proposed to include a secondary opening in the assessment method to evaluate the detailing of the façade system around openings. In the proposal the secondary opening is moved towards the edge of the main face of the test specimen.
This is done in order to be able to evaluate the façade with and without secondary opening during the test. This has not yet been verified and needs to be examined during the next step of the project.
For the Proposed assessment method a secondary opening may be included in the test set-up, to assess the mounting and behaviour of the façade system around openings. The secondary opening is optional in the Proposed assessment method.
For the Alternative assessment method a secondary opening shall be included in the test set-up, to assess the mounting and behaviour of the façade system around openings. This secondary opening is mandatory in the Alternative assessment method.

| JUNCTION BETWEEN FAÇADE AND FLOORS
In some national test methods are also details such as the junction between floor and façade included and assessed. It concerns only the façade systems installed directly connected to floors of a building. It is therefore proposed for these specific façade systems to include a junction in the test method in order to evaluate the risk that the fire goes through the junction.
For concerned façade systems, a specific adaptation of the combustion chamber ceiling is done in the test.
This measurement and classification is optional for the Proposed assessment method.
For concerned façade systems, a specific adaptation of the combustion chamber ceiling is done in the test.
This measurement and classification is optional for the Alternative assessment method.

| MEASUREMENT OF FIRE SPREAD
The methods used to evaluate the fire spread in and on After this time the fire in the combustion chamber will be extinguished, and an additional 30 or 38 minutes of observations and measurements will be made, that is, a total test time of 60 minutes after the test time has been reached. This needs to be addressed in the coming studies and preferable result in a transparent system where the same procedures and times are used.
As a demonstration in Figure 1, the Alternative assessment method is shown schematically.

| CLASSIFICATION
For classification large differences between the Proposed and the Alternative assessment method exist. The Proposed assessment method has been optimized on the use of historical data which has the drawback that the classification system will be more complicated.
The Alternative assessment method on the other hand has been optimized to get as few classes as possible, that is, to have a very simple classification system.
The classification system for the Proposed assessment method contains six different characteristics that may be included in the classification, see Table 4. Only the heat exposure is mandatory, all other characteristics are optional. For the Alternative assessment method, a general comment from stakeholders on the classification was followed that a simple system, with as few classes as possible, is desirable. It is judged that is the classification system presented in Table 5.
Some classes in the system will also cover other classes as follows: -A classification in class LS1 also cover classes LS2, LS3 and LS4 -A classification in class LS2 also cover class LS4 -A classification in class LS3 also cover class LS4

| NEXT STEPS FOR HARMONIZATION
The next steps of European harmonization are now: to perform a second European project which has started in March 2020 with Round Robin tests to assess repeatability and reproducibility of the finally retained Alternative assessment method

| FURTHER STUDIES
Further studies are needed to ensure that the Alternative assessment method method has good enough repeatability and reproducibility.
There are several factors that must be studied, such as: -Effect of environment (especially wind speed and direction).
-Tolerances needed for the fuel (the research community do not agree on the repeatability of wood cribs, especially on the size needed for these types). Factors affecting are timber species, conditioning of the timber, density of the individual timber sticks, dimensions of sticks, amount of timber, and the tolerances needed.
-Mounting of samples and representatives substrates for systems not intended to be mounted on masonery.
-Mounting of thermocouples. There is a disagreement on how to mount the thermocouples in the best way, by drilling through the test specimen, or hanging them from the outside. Both methods have pros and cons. This is also sensitive for measurement of smouldering as new criteria introduced by this work.
-Measurement of heat exposure to the test specimen. It is important that the heat exposure can be reported after a test. There are different options such as measurement of temperature with plate thermometers pointing towards the fire, heat flux gauges measuring the radiation or mass loss measurement of the fuel source. A suitable method needs to be developed and validated.
-External fire. In some Member States is the external fire scenario used. It may be that the proposed methods would work well also for external fires such wildland fire scenarios or vehicle fires, but this needs to be validated.