Today, mankind uses a wide variety of combustible substances. There are already quite a few types of them and they all have some kind of their own, unique characteristics. What are these substances? This is the raw material that can continue to burn after the ignition source is removed.
Gases and liquids
Today, there are several groups of combustible substances.
You can start with the gases - the GG group. This category includes those substances that can be mixed with air, forming an explosive or flammable atmosphere, at a temperature not exceeding 50 ° C. In this group of gases, certain individual volatile compounds can be attributed. It can be ammonia, acetylene, butadiene, hydrogen, isobutane and some others. Separately, it should be said that this also includes vapors that are released during the evaporation of flammable liquids (flammable liquids), representing the following category.
The flammable liquid group includes those liquid combustible substances that will continue to burnafter removal of the ignition source, and also their flash point does not exceed the threshold of 61 degrees Celsius for a closed cup. If this vessel is of an open type, then the threshold will rise to 66 degrees. Such liquid substances include acetone, benzene, hexane, heptane, isopentane, styrene, acetic acid and many others.
Flammable liquids and dusts
It would seem that a flammable liquid and a combustible one and the same thing, but in practice it turned out not to be the case. They are divided into two different categories. Even though their ignition parameters are the same and some liquids belong to both groups, there is a main difference. GZH also includes oil-based substances. This, for example, can be castor or transformer.
Next, it is worth mentioning such a combustible substance as dust. HP is a solid substance, which is currently in a finely dispersed state. Once in the air, such dust can form an explosive structure with it. If such particles settle on walls, ceilings and other surfaces, they may cause a fire.
GP classes
It is worth noting separately that there are classes of combustible substances and materials. For example, dust is divided into three categories depending on the degree of fire and explosion hazard.
- First class - these are the most dangerous aerosols with a lower explosive (flammable) limit (LEL) of up to 15 g/m3. Hereinclude sulfur, mill, ebonite or peat dust.
- The second class includes those particles whose LEL limit is in the range from 15 to 65 g/m3. They are considered more explosive.
- The third category is the most fire hazardous. This is a group of liquid aerogels, in which the LEL is more than 65 g/m3, and the autoignition temperature is up to 250 degrees Celsius. Such properties are possessed by tobacco or elevator dust, for example.
General Features
Which combustibles are and why? There are several specific characteristics, with which liquid, dust, gases and other substances can be classified as combustible.
For example, the degree of flash is a value that characterizes the lower temperature limit, at which the liquid will form flammable vapors. However, it should be noted here that the presence of a fire source near such a vapor-air mixture will only cause its combustion, without a stable burning effect of the liquid itself.
If earlier it was said about the lower concentration limit, then there is also the upper one. NKV or VKVV are, respectively, the values upon reaching which, ignition or explosion of liquid, dust, gases, etc. can occur. All types of combustible substances have these limits. However, it is important to note here that if the concentration is lower or, conversely, higher than the specified limits, then nothing will happen even if there is a source of open fire in the immediate vicinity ofsubstances.
Solid raw materials
Here it is worth mentioning that solid combustible substances behave somewhat differently than dust, liquid or gas. When heated to a certain temperature, this group of raw materials behaves individually, and this depends on its characteristics and structure. For example, if you take sulfur or rubber, then when heated, they first melt and then evaporate.
If you take, for example, wood, coal or paper and some other substances, when heated, they begin to decompose, leaving behind gaseous and solid residues.
Another very important point: the composition of combustible substances and their chemical formula greatly affects the direct combustion process itself. There are several stages into which this phenomenon is divided. Simple substances such as anthracite, coke or soot, for example, heat up and smolder without any sparks, since their chemical composition is pure carbon.
Complex combustion products include, for example, wood, rubber or plastic. This is due to the fact that their chemical composition is quite complex, and therefore there are two stages of their combustion. The first stage is a decomposition process that is not accompanied by the usual release of light and heat, but the second stage is already considered burning, and at this time heat and light begin to be released.
Other substances and characteristics
Of course, solids also have a flash point, but for obvious reasons, itmuch higher than that of liquid or gaseous substances. Flash point limits are between 50 and 580 degrees Celsius. It is worth mentioning separately that such a common combustible material as wood has a threshold of 270 to 300 ° C, depending on the species of the tree itself.
Gunpowder and explosives have the highest combustion rate among solids. This is due to the fact that both of these substances have a sufficiently large amount of oxygen, which is quite enough for their complete combustion. In addition, they may well burn underwater, underground, as well as in a completely sealed environment.
Wood
It is worth saying a little more about this combustible solid material, as it is one of the most common today. The reason for this is that it is one of the most affordable. Here it is worth mentioning that in fact wood is a substance with a cellular structure. All cells are filled with air. The degree of porosity of any rock exceeds 50% and increases, which indicates that the concentration of solid matter in relation to air is not too high. It is because of this that it lends itself to burning quite well.
If we conclude, we can say that in the world there are a large number of various combustible substances that cannot be dispensed with in everyday life, but at the same time, one must be extremely careful when using them, using them only for their intended purpose.
