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.
In the future, a common system of fire testing (reaction to fire and fire resistance) and classification of the resulting test data for construction products will be implemented across the EU member states.
During the transition period, both BS and EN references will be commonplace and are referenced in 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
BS 476: Part 4: 1970 Non-combustibility test for materials
This test 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
This test 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
This test 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
This standard 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.
Class 0 (As defined in Approved Document B)
a) Composed throughout of materials of limited combustibility, or
b) A Class 1 (to BS 476: Part 7: 1987) material which has a fire propagation index (I) of not more than 12, and a sub-index (i1) of not more than 6 (to BS 476: Part 6: 1989).
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:
1. 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.
2. The Hydrocarbon Curve
This curve is a 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.
3. The RABT Curve
This curve was 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.
4. 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.
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 (R)
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.
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.
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).
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.