It is a fact that wood is an organic substance and thus a combustible material. Often, however, the fact that properly-sized wooden structures possess significantly greater fire resistance than usually attributed to wood is ignored. Thus, a wooden structure can also exceed the fire resistance of steel and reinforced concrete. The ability of wood to conduct heat is very small, as it transfers heat 300 to 400 times slower than steel. The load-bearing capacity of steel that is not fire protected begins to decrease at a temperature of about 230 °C, is halved at 500 °C and only 10% of the capacity is remaining at 750 °C.
Fire results in wood carbonising at a typical estimated rate of 0.6 mm per minute, a fact which is considered when planning the dimensions of wooden structures. Elements of wood thus carbonise slowly from the surface towards the interior, which prevents oxygen from accessing the wood. Elements in non-carbonised cross-sections therefore retain their full load-bearing capacity and do not change shape during burning and therefore do not cause pressure or load transfer on the other structural elements, which is predominantly the reason structures collapse. In addition to the stated, Marles wooden structures are insulated with non-flammable stone wool, and both sides of the structure are slabbed with non-flammable gypsum boards or fire-resistant wooden boards, which further prevents fire access to the wooden structure of the building. A Marles house is therefore safe to live in, as it functions safely and predictably despite the flammability of wood.
Fire protection – Marles houses provide greater fire protection than required by regulations at the European Union level.
The fire properties of all of the main structural construction elements of Marles houses have been proven with tests carried out in a fire laboratory in Vienna, resulting in their certification by OIB (Österreichisches Institut für BAUTECHNIK, member of the European Organisation for Technical Approvals) proving the adequacy of Marles buildings’ fire safety. With regard to the stated, we wish to emphasize the fact that all tested elements surpassed the norms and the predicted time frames of fire resistance. Differently put, even after the conclusion of the tests due to the already established fire resistance, the elements maintained their resistance to the fire to which they were exposed during the testing procedure.
An additional argument supporting the fire safety of Marles buildings can also be made based on the fact that Marles elements for the construction of houses meet the fire-safety standards that are prescribed at the EU level for the construction of schools and kindergartens and which significantly surpass the requirements relating to the construction of common residential buildings.
Wood is harder than steel
As an organic substance, wood is a flammable material. However, with regard of the fire safety of an element or building, flammability thereof is not as important as its “resistance to burning”.
We thus see burnt beams at burn sites that are still standing upright and carrying their load (see figure), which is also due to their resistance to burning, meaning that if properly sized and protected wood will burn in a controlled way and retain its structural strength for a predictable period of time.
In the case of steel, the situation is different. When steel exceeds a certain temperature (over 500 °C), it enters the area of plasticity, no longer retains its own load-bearing capacity and dimensionally deforms and suddenly completely collapses. Before a wooden construction collapses in a fire, a great deal of crackling is heard, thus allowing enough time for persons to evacuate the building. Steel, on the other hand, losses its hardness quickly and in most cases collapses with no prior warning. Wood burns out slowly, thus leaving its interior undamaged and still performing its task as a load-bearing construction element (see graph). Therefore, wood maintains its hardness in fires longer than steel.
The graph below demonstrates the comparison of the loss of hardness in a steel construction and in a wooden construction:
Nosilnost: load capacity
Minute: minutes
50 % manjša v 10 minutah: 50% decrease in 10 minutes
25% manjša v 30 minutah: 25% decrease in 30 minutes
90% manjša v 30 minutah: 90% decrease in 30 minutes
jeklo: steel
les: wood
