Many of the member countries of the European Union (EU) have adopted the harmonized Euroclass system of reaction to fire performance of building products. The background of the harmonization process lies on the Commission Decision 94/611/EC implementing Article 20 of Directive 89/106/EEC on construction products [39] in the field of fire safety. The Euroclass decision includes a classification system for building products based on their reaction-to-fire performance. It additionally defines the test methods according to which construction products shall be categorised. In the Euroclass system, floor coverings and other surface linings are considered separately.

The purpose of harmonization is to facilitate the trade of building products between the member countries of the EU by removing trade barriers due to differences in test methods and classification systems. Previously, products had to be tested and classified according to national standards in each country in which they were launched to the market. In the new system, the Euroclass classification of a product is acknowledged in all member countries based on its performance in the harmonized fire tests.

The decision on the classification of the reaction to fire performance of construction products [40] was published in February 2000. The Euroclass system requires including the test methods and classifications of the Euroclass decision in the legislation of the member countries. The required fire performance for various purposes of use of construction products are still decided nationally, but the requirements are expressed in terms of harmonized standards.

This section is organized as follows:

1. Test methods

The European classes of reaction to fire performance for construction products excluding floorings are based on four fire test methods: the non-combustibility test EN ISO 1182 [41], the gross calorific potential test EN ISO 1716 [42], the single burning item (SBI) test EN 13823 [43], and the ignitability test EN ISO 11925-2 [44]. The same test methods, excluding the SBI test, are used for floorings with the addition of the radiant panel test EN ISO 9239-1 [45]. The details of specimen conditioning and substrate selection are given in EN 13238 [46], and the harmonized procedure for the classification is described in EN 13501-1 [47].

The first two test methods below are only applicable for non-combustible materials. Fire retardant wood products cannot reach these criteria.

1.1. Non-combustibility test EN ISO 1182

The purpose of the non-combustibility test EN ISO 1182 is to identify the products that will not, or significantly not, contribute to a fire. The test apparatus is shown in Figure 6a. A test specimen of cylindrical shape is inserted into a vertical tube furnace with a temperature of about 750 °C. Temperature changes due to the possible burning of the specimen are monitored with thermocouples. The flaming time of the specimen is visually observed. After the test, the mass loss of the specimen is determined.

The quantities used in the European classification are the temperature rise of the furnace (∆T), the mass loss of the specimen (∆m), and the time of sustained flaming of the specimen (tf).

1.2. Gross calorific potential test EN ISO 1716

The gross calorific potential test EN ISO 1716 determines the potential maximum total heat release of a product when burned completely. The test apparatus is shown in Figure 6b. A powdery test specimen is ignited in pressurized oxygen atmosphere inside a closed steel cylinder (calorimetric bomb) surrounded by water jacket. The temperature rise of water during burning is measured. The gross calorific potential is calculated on the basis of the temperature rise, specimen mass, and correction factors related to the specific test arrangement used.

The classification parameter of the method is the gross calorific potential (PCS) measured in MJ/kg or MJ/m2 depending on the features of the product and its components.

1.3. Single Burning Item test EN 13823

The SBI test is a relatively new fire test method developed specially for the Euroclass system. The test is based on a fire scenario of a single burning item, e.g. a wastebasket, located in a corner between two walls covered with the lining material to be tested. The SBI test is used for construction products excluding floorings.

The SBI test was developed by a group of European fire laboratories on the basis of the specifications defined by a group of European fire regulators. The development work included the design of a prototype, the installation of test facilities, the determination of the accuracy of the method, and the production of data needed to finalise the classification system [48].

SBI test specimens are installed on a specimen holder with two vertical wings made of non-combustible board. The specimen holder wings of sizes 1,0 m × 1,5 m and 0,5 m × 1,5 m form a right-angled corner configuration. The thermal exposure on the surface of the specimen is produced by a right-angled triangle-shaped propane gas burner placed at the bottom corner formed by the specimen wings. The heat output of the burner is 30 kW resulting in a maximum heat exposure of about 40 kW/m2 on an area of approximately 300 cm2. The burner simulates a single burning item. Combustion gases generated during a test are collected by a hood and drawn to an exhaust duct equipped with sensors to measure the temperature, light attenuation, O2 and CO2 mole fractions and flow-induced pressure difference in the duct. The test apparatus is shown schematically in Figure 6c, and a photograph of a test in Figure 6d.

The performance of the specimen is evaluated for an exposure period of 20 minutes. During the test, the heat release rate (HRR) is measured by using oxygen consumption calorimetry. The smoke production rate (SPR) is measured in the exhaust duct based on the attenuation of light. Falling of flaming droplets or particles is visually observed during the first 600 seconds of the heat exposure on the specimen. In addition, lateral flame spread is observed to determine whether the flame front reaches the outer edge of the larger specimen wing at any height between 500 and 1000 mm during the test.

The classification parameters of the SBI test are fire growth rate index (FIGRA), lateral flame spread (LFS), and total heat release (THR600s). Additional classification parameters are defined for smoke production as smoke growth rate index (SMOGRA) and total smoke production (TSP600s), and for flaming droplets and particles according to their occurrence during the first 600 seconds of the test.

The FIGRA and SMOGRA indices are calculated as follows:

where HRRav is the heat release rate averaged over 30 seconds (in kW), SPRav is the smoke production rate averaged over 60 seconds (in m2/s), and t is the time elapsed after the beginning of the test (in s), i.e. the ignition of the burner. The units of FIGRA and SMOGRA are W/s and m2/s2, respectively. Constant coefficients are added to the definition of the parameters to obtain convenient ranges of numbers. Different heat release related threshold values for the FIGRA calculation are used in different classes to obtain FIGRA0,2MJ and FIGRA0,4MJ values. Also SMOGRA calculation includes certain smoke production related threshold values, common to all smoke production classes.

The THR600s and TSP600s values are calculated over the first 600 seconds of the test as follows:

where HRR(t) and SPR(t) are the heat release rate and smoke production rate as functions of time (in kW and m2/s, respectively), and ∆t is the data acquisition interval of the measurement (in s). The units of THR600s and TSP600s are MJ and m2, respectively.

1.4. Ignitability test EN ISO 11925-2

In the ignitability test EN ISO 11925-2, the specimen is subjected to direct impingement of a small flame. The test specimen of size 250 mm × 90 mm is attached vertically on a U shaped specimen holder. A propane gas flame with a height of 20 mm is brought into contact with the specimen at an angle of 45 °. The application point is either 40 mm above the bottom edge of the surface centreline (surface exposure) or at the centre of the width of the bottom edge (edge exposure). Filter paper is placed beneath the specimen holder to monitor the falling of flaming debris. The test apparatus is shown in Figure 6e.

Two different flame application times and test durations are used depending on the class of the product. For class E, the flame application time is 15 seconds, and the test is terminated 20 seconds after the removal of the flame. With a flame application time of 30 seconds for classes B, C and D, the maximum duration of the test is 60 seconds after the removal of the flame. The test is terminated earlier if no ignition is observed after the removal of the flame source, or the specimen ceases to burn (or glow), or the flame tip reaches the upper edge of the specimen.

The classification criteria are based on observations whether the flame spread (Fs) reaches 150 mm within a given time and whether the filter paper below the specimen ignites due to flaming debris. In addition, the occurrence and duration of flaming and glowing are observed.

1.5. Radiant panel test EN ISO 9239-1

In the radiant panel test EN ISO 9239-1, a test specimen of size 1050 mm × 230 mm is placed horizontally below a gas-fired radiant panel inclined at 30 °. The specimen is exposed to a defined field of total heat flux, 11 kW/m2 at the hotter end close to the radiant panel, and decreasing to 1 kW/m2 at the other end farther away from the radiant panel. A pilot flame front from a line burner is applied to the hotter end in order to ignite the specimen. The test apparatus is presented in Figure 6f.

The progress of the flame front along the length of the specimen is recorded in terms of the time it takes to travel to various distances. The smoke development during the test is measured on the basis of light obscuration by smoke in the exhaust duct. The duration of the test is 30 minutes.

The classification criterion is the critical heat flux (CHF) defined as the radiant flux at which the flame extinguishes or the radiant flux after a test period of 30 minutes, whichever is lower. In other words, CHF is the flux corresponding to the furthest extent of spread of flame.

Figure 6. The test apparatuses for the European classification: a) test for non-combustibility and b) test for gross calorific potential, c) SBI test, a schematic drawing, d) SBI test, photograph, e) test for ignitability of building products subjected to direct impingement of flame and f) test for floorings.

2. Classes and criteria

In the Euroclass system, building products are divided to seven classes on the basis of their reaction-to-fire properties. The performance description and the fire scenario for each class are presented in Table 6 according to the main principles used in the development of the Euroclass system (not given in the final decision).

Table 6 includes some examples of typical building products used in walls and ceilings in each Euroclass. It is noted that certain materials containing only a very small amount of organic compounds are deemed to satisfy the requirements of class A1 without testing. Examples of such materials are concrete, steel, stone and ceramics [49].

The decision on the classification of the reaction to fire performance of construction products [40] was made in February 2000. The test methods and classification criteria are presented in Table 7 for construction products excluding floorings and in Table 8 for floorings.

The highest possible European class for fire retardant wood products is class B.

Table 6. Indicative performance descriptions and fire scenarios for Euroclasses.

Table 7. Classes of reaction to fire performance for construction products excluding floorings [40]. The abbreviations of classification parameters are explained in the text.

Table 8. Classes of reaction to fire performance for floorings [40]. The abbreviations of classification parameters are explained in the text.