Fire burning problem or just a cool calculation?
In Poland and some countries dominates an opinion that wood construction houses are exposed to higher risk of inflammability. However, the construction is not the threat – it is only a matter of preparation of partition of walls and materials used for protection. In conclusion, is the myth a fact or is it busted? How about our construction GreMagor?
A little bit of theory
Materials used for construction have to meet the requirements of the EU directive 89/106/EWG. It’s regulation on Polish market is the normalization act PN-EN 13501-1. Within its frames there is a categorization of materials in terms of inflammability. It is divided into classes – starting from A1, A2, B up to F. The A1 is the best resistance and F is worst. There are also additional parameters like smoke emission (s1, s2, s3, where s1 is non smoking and s3 means intensive smoke emission) or firing drops emission (d0 to d2, where d0 means no drops, while d2 means firing drops).
Each material used for the construction should have a classification in term of fire resistance.
How does it look like in practice?
Wood-based construction walls have mostly a multi-layer construction. It means that wood is the core, while the elements protecting it are the additional materials on the outside and inside of walls. The construction wood itself has a D-s2,d0 class which means that it burns not earlier than 2 minutes after exposure to heat stream of 100 kW, has a mid-range emission of smoke and does not generate firing drops. Such good class is possible to achieve due to the preparation process of wood based on 4-sided planing, which makes the wood harder to ignite. The use of impregnation may increase the fire resistance up to class B, which means “no flashover” – after the removal of source of heat it should go out. In Gremagor system we use construction wood C24 which fits the proper norms and may be impregnated if a customer wants to. In our system 95% of the wall interior is fulfilled with insulation material, mostly rock wool, which is responsible for the behavior of fire. In case of usage of rock wool with A1 class, interior of the wall is nonflammable. It means that fire has a difficult task to reach the construction, especially if it acts on one point. What is important, wood based construction should maintain its properties in a high percentage even if it is totally burned into form of charcoal, which gives more time for evacuation.
Sources of fire and behavior of additional materials
Before the fire reaches construction it has to find a way to reach it. It would require:
– intentional activity,
– faulty electric installation or similar,
– activity from the inside, due to the fire inside the building.
In case of external insulation it is difficult to fire it up. For example, even materials with class E are covered with plaster, which gives some resistance. Some facade plates have a class A or B, which means that they are really hard to burn. Usage of materials of A and B class gives more probability of being incombustible – in practice, material used for intentional flaming of the building should burn out, while the facade should remain safe of fire if the exposure is short-term.
In case of threat from installations today’s solutions minimize the risk almost to zero. When the installation has a short-circuit, main threat is the heat generated from this occurrence. Such material may reach up to several hundred degrees, which may be the source of fire. Today electric installations are mounted in special, nonflammable conduits having the purpose of insulation from the risk of fire spread. There are also special construction of wires, which are nonflammable. If the fuses installation works properly, it should switch-off the source of energy and then the heating should stop, without any further damage.
The biggest threat is the fire source inside. There are a lot of reasons of it – for example accident, inflammation of the oil in a frying pan, inflammation of the curtains, carpets or just leaving the butts in bed while falling asleep. In such case most important is the fire resistance since the construction lights up. For the internal side of wall mostly used are plaster boards (with class A or B) or other materials with class A or B. They often have a special fire classification called “EI”, which means resistance to continuous fire. The standard types of plaster board remain nonflammable up to 30 minutes of continuous fire. The more thickness or more complex construction of these plaster boards, the higher the resistance. In such cases, fire brigade should extinguish the fire, while the construction should remain intact, which gives the proper field for evacuation.
So, cold calculation?
The usage of modern solutions like GreMagor in connection with proper construction of walls should give at least the same resistance to fire as classical forms of construction.