The importance of testing

Historically, each country in the European Union has developed its own fire tests in support of its national building regulations. In the UK, these methods are British Standards.

A common system of fire testing (reaction to fire and fire resistance) and classification of the resulting test data for construction products has been implemented across the EU member states. During the transition period, both BS and EN reaction to fire and fire resistance methods are referenced in Building Regulations Approved Document B. The following section shows both BS and EN test methods.

Reaction to Fire (RtF) tests tell us how a product will become involved in the growth of fire in the room of origin, up to the time when flashover occurs, or does not occur. The data from specific small/intermediate reaction to fire test methods is assessed and provides a fire classification for the material.

Fire resistance tests tell us how an element of construction or fire protection system will prevent a fully developed fire from causing structural collapse of the element, or prevent the fire from passing from the room of origin into an adjacent room, corridor or other space.

Test on materials

British Standard (BS) Reaction to Fire Classification

BS 476: Part 4: 1970 Non-combustibility test for materials: classifies materials as either ‘non-combustible’ or ‘combustible’. It is the most stringent standard for the fire performance of materials and gives a measure of the heat and flames generated by the material under standard heating conditions. Non-combustible materials can be used without restriction anywhere in a building. Their use ensures that hazards due to smoke and toxic gases are minimised and that the fabric of a building will not make a contribution to a fire.

BS 476: Part 6: 1989 Method of test for fire propagation for products: measures the amount and rate of heat evolved by the product while subjected to standard heating conditions. Test results are given as an Index of Performance (I) which is based on three sub-indices (i1, i2, i3). The higher the value of the Index, (I), the greater the material contribution to fire growth. The higher the value of the sub-index, i1 the greater the ease of ignition and flame spread.

BS 476: Part 7: 1987 Method for classification of the surface spread of flame for products: classifies materials into Classes 1 to 4 in descending order of performance according to the rate and extent of flame spread over their surface under standard heating conditions. All Promat board products have the highest rating of surface spread of flame, i.e. Class 1.

BS 476: Part 11: 1982 Method of assessing the heat emissions from building materials: describes a method for assessing the heat emissions from building materials when inserted into a furnace at a temperature of 750°C. It is similar to BS 476: Part 4: 1970 but differs in that Part 4 classifies the material as “combustible” or “non-combustible” whereas Part 11 criteria are specified in Approved Document B, leading to classification as a material of limited combustibility.

European Reaction to Fire Classification

Evidence obtained from test results allow the products to be classified according to BS EN 13501-1: Fire Classification of Construction Products and Building Elements: Part 1: Classification using test data from reaction to fire tests.

BS EN ISO 1182 Non-Combustibility Test: the purpose of the non-combustibility test BS EN ISO 1182 is to identify the products that will not, or significantly not, contribute to a fire. A test specimen of cylindrical shape is inserted into a vertical tube furnace with a temperature of about 750^°C. Temperate 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).

BS EN ISO 1716 Gross Calorific Potential Test: the gross calorific potential test BS EN ISO 1716 determines the potential maximum total heat release of a product when burned completely.  A powdery test specimen is ignited in pressurised 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.

BS EN 13823: Single Burning Item (SBI) Test: the reaction to fire test method used as part of determining European classes A2, B, C and D.  It is always conducted in addition to other European reaction to fire test methods. The single burning item test was originally developed to simulate a wastepaper basket fire.  It utilises a 30kW burner in the corner of a room that is lined by the material or product which is to be classified.  External wall claddings can also be tested in the same way even though some buildings may not have such an “internal” corner detail in reality.

The test method analyses the products of combustion.  From this data, calculations are made to determine Total Heat Release (THR) and Fire Growth Rate (FIGRA).  How quickly a fire develops and how much heat energy is produced are the crucial factors in determining the ease of evacuation from a building.  These values are then used to determine the class (A2, B, C or D).

A Lateral Flame Spread (LFS) observation is used to see whether flames spread across the test specimen’s long wing during the test.  If this occurs beyond specified limits, the product or material can only reach a European class D.

Measurement of the smoke produced and observation of any flaming droplets or particles are used to determine the additional classifications s1 to s3 and d0 to d2.

European Reaction to Fire Testing Standards

BS EN ISO 11925-2: Single Flame Ignitability (SFI) Test: simulates a cigarette lighter size flame being placed upon either the surface or the edge of the specimens for a short duration (15 or 30 seconds).  The time to ignition and the time until the flames spread up and exceed 150mm above the flame application point are recorded.  These results on their own are then used to determine classification to E or potentially F. This test is used in conjunction with the SBI test for classes B, C and D.

The table below shows which European reaction to fire test evidence is required to gain each European classification.

Fire testing methods

The fire performance of any system will vary depending on the heating conditions to which it is exposed. National and international fire curves have been developed for differing fire exposures. Examples of fire curves carried out in test furnaces by recognised national organisations are as follows:

The Standard Cellulosic Time-Temperature Curve (ISO 834): this ISO-based curve is used in standards throughout the world, including BS 476, AS 1530, DIN 4102, ASTM and the new European Norm (BS EN 1363-1). It is a model of a ventilated controlled natural fire, i.e. fires in a normal building. The temperature increase after 30 minutes is 842°C.

The Hydrocarbon Curve: simulation of a ventilated oil fire with a temperature increase of 1110°C after 30 minutes. The Hydrocarbon Curve is applicable where petroleum fires might occur, i.e. petrol or oil tanks, certain chemical types etc. In fact, although the Hydrocarbon Curve is based on a standardised type fire, there are numerous types of fire associated with petrochemical fuels, which have wide variations in the duration of the fire, ranging from seconds to days.

The RABT Curve: developed in Germany as a result of a series of test programmes such as the Eureka project. In the RABT Curve (car), the temperature rise is very rapid up to 1200°C within 5 minutes. The duration of the 1200°C exposure is shorter than other curves with the temperature drop off starting to occur at 60 minutes. The curve relating to trains is also shown.

The RWS Curve (Rijkswaterstaat), NL: this model of a petroleum based fire of 300MW fire load in an enclosed area such as a tunnel, has been developed in the Netherlands and is specified for use in tunnels. It is internationally accepted. The temperature increase after 30 minutes is 1300°C.

British Standard (BS) fire testing performance

Fire resistance is not a property of an individual material but is the measure of the performance of a complete system or construction when exposed to standard heating conditions. The failure criteria of elements of building construction when tested in accordance with BS 476: Parts 20-24 are as follows:

Loadbearing Capacity: the ability of a specimen of a loadbearing element to support its test load, where appropriate, without exceeding specified criteria with respect to either the extent of, or rate of deformation, or both.

Integrity: the ability of a specimen of a separating element to contain a fire to specified criteria for collapse, freedom from holes, cracks and fissures and sustained flaming on the unexposed face.

Insulation: the ability of a specimen of a separating element to restrict the temperature rise of the unexposed face to below specified levels (usually 140°C mean rise, 180°C maximum rise).

Stability: the ability of a ductwork system to maintain its intended function. The above references (R, E and I) are commonly used within the fire protection industry when referring to BS 476 methods, however, they are actually European EN terms, as opposed to British Standard terms.

European Fire Resistance Classes

The classification of construction products and building elements provides a means of expressing the fire resistance of these elements.

Classification According to the Direct Field of Application (DIAP): is based on data from fire resistance and smoke leakage tests which are within the direct field of application of the relevant test standard (in accordance with the classification standard EN 13501)

Designation of the Fire Resistance Class: the fire resistance class is indicated by means of a combination of letters and numbers. The letters refer to the different performance parameters, as far as those apply to the element in question.

The performance parameters are:

• R: Loadbearing Capacity
• E: Integrity
• I: Thermal Insulation
• W: Limitation of Radiation
• M: Mechanical Resistance
• C: Self Closure
• S: Smoke Leakage
• G: Soot Fire Resistance
• K: Fire Protection

During the test, it is determined how long the building element preserves the tested performance when exposed to fire. Each performance has a number of criteria which determine when a building element loses that performance (see below). Based on the test, the building element is assigned one of the following fire resistance classes: resistance to fire during 15, 20, 30, 45, 60, 90, 120, 180, 240 or 360 minutes.

Loadbearing Capacity (R): the ability of the construction element to withstand specified mechanical actions whilst being exposed to fire, at one or more sides, during a determined period of time, without loss of structural stability. The criteria applied to determine the loss of stability, vary according to the type of load bearing element:

• For flexurally loaded elements, such as floors, roofs:
  • A rate of deformation (rate of deflection)
  • A limit state of the actual deformation (deflection)
• For axially loaded elements, such as columns, walls:
  • A rate of deformation (rate of contraction)
  • A limit state for the actual deformation (contraction).

Integrity (E): the ability of the construction element with a separating function to withstand exposure to fire on one side without fire propagation to the unexposed side as a consequence of flaming or the passage of hot gases. The integrity is evaluated on the basis of the following three aspects:

• Cracks or openings exceeding the given dimensions
• Ignition of a cotton pad
• Sustained flaming on the unexposed side.

Thermal Insulation (I): the ability of the construction element to withstand exposure to fire on one side without fire propagation to the unexposed side as a consequence of heat transfer. Thermal insulation limits the heat transfer as a result of which neither the unexposed side nor adjacent materials will ignite.

Limitation of Radiation (W): the limitation of radiation is the ability of a construction element - when exposed to fire on one side - to reduce the probability of fire propagation as a consequence of a significant heat radiation, either through the element or from the unexposed surface to adjacent materials. The limitation of heat radiation is determined by the period of time for which the maximum value of radiation, measured as specified in the test standard, does not exceed the limit value of 15kW/m².

Mechanical Resistance (M): the ability of a construction element to withstand an impact representing the effect caused by the structural failure of an other component. The element is subjected to a predefined impact shortly after it has been tested to determine its load bearing capacity, integrity and/or thermal insulation. The element should resist the impact without prejudice to the R, E and/or I performance.

Self Closure (C): the ability of an open door or window to close fully and to engage a fitted latching device, without human intervention so only by stored energy or by means of electricity backed by a system of stored energy in case of power failure. This applies to elements that are mostly closed and should close automatically when opened and to elements that are mostly open and should close automatically in case of fire.

Smoke Leakage (S): the ability of a construction element to reduce or eliminate the passage of hot/cold gases or smoke from one side of the element to the other.

Soot Fire Resistance (G): the ability of a chimney or related construction elements to withstand soot fire. This includes aspects of smoke leakage and thermal insulation.

Fire Protection (K): the ability of a wall or ceiling covering to provide protection against ignition, charring and other damage to the materials behind the coverings for a specified period of time. Coverings are the outer surfaces of construction elements such as walls, floors and roofings.

Classification According to the Extended Field of Application (EXAP)

A classification based on the extended field of application is not covered by the above referenced standard (EN 13501), but it is assigned according to the European Standard EN15524. The designation of the classification is nevertheless the same as specified in the classification standard.