Any common fire, either Solid fire (A-class fire), or Liquid fire (B-class fire), or Fat fire (F-class fire) are only gas fires.
For example, the exposure of a piece of wood to a heat source will enable the start of the cellulose decomposition (see below).
A wood fire is therefore and firstly a gas fire.
a) The two main reaction pathways of thermal decomposition of wood :
b) Splitting of cellulose molecules in the tar-forming reaction (normal combustion) :
c) Splitting of cellulose molecules in the char-forming reaction :
The pyrolysis of wood is dependent on external factors, such as the way of heating, warming-up rate of the material, etc. Therefore, wood products do not have an explicit ignition temperature,
but ignition takes place on a certain temperature range where the probability of ignition becomes large enough. The temperature for the piloted ignition of wood is typically about 350 °C,
whereas the spontaneous ignition requires a temperature of approximately 600 °C.
Heat released in combustion is the driving force of a fire: the larger the heat released by a burning object is, the faster the fire spreads and the hotter the gases and limiting surfaces of
the fire enclosure become. Thus, one of the most essential quantities describing the burning of materials is the rate of heat release, denoted with Q and expressed in kW.
In addition to the internal structure and properties of a material, the rate of heat release is strongly dependent on external factors.
Therefore, exact Q values for different materials cannot be given.
The most important external factors having an effect on Q are the net heat flux q"net to the surface and the oxygen concentration of the ambient, described with the factor ƒ(O2).
The internal properties of a material affecting on Q are the heat of combustion ΔHc, the heat of gasification Lv, and the specific heat capacity C.
The following equation shows the rate of heat release per unit area of a burning material:
where Tig is the ignition temperature and T0 is the ambient temperature. It is noted that, in addition to the incoming heat flux on the surface,
q"net is also dependent on the heat losses from the surface.
Oil as product does not burn.
The heat increase enables production of flammable vapours, and only these vapours are burning.
A liquid fire is once again a gas fire.
The same demonstration can be done with fat elements, the strong temperature increase will lead to vapour production, and even to auto-ignition.
A fat fire is also a gas fire.
UNITEQ has studied inflammation mechanisms of class A, B and F materials.
The fire suppression comes foremost with a surface treatment of the burning material to restrict vapour diffusion and then stop the fire.
With this expertise of the surface treatment, especially on A-class fires, UNITEQ now proposes 2 ranges of products:
1 - Fire-prevention
2 - Fire-suppression
