Today, there is a specially developed standard that sets the symbols and classes of fires - GOST 27331-87. This document allows you to determine the type of combustion process and select the most effective means for extinguishing it. According to the conditions of heat and mass transfer with the environment, fires occur in fences and in open spaces. And depending on the type of burning substances and materials, they can be divided into classes and subclasses, which we will discuss in detail in our article.
What classes are fires divided into?
1) Class A - combustion of solid combustible materials and substances. In this case, if wood, textiles or paper smolders, the fire belongs to subclass A1, and if non-smoldering material, such as plastic, burns, to subclass A2.
2) Class B is composed of flammable combustible liquids: insoluble - subclass B1, soluble - B2.
3) Class C fires are fired by gases.
4) Class D - metal combustion. Moreover, light metals belong to the subclass D1, alkaline are designated D2, and metal-containing compounds - D3.
5) Class E - burning electrical installations that are energized.
6) Class F- fires of radioactive waste and nuclear materials.
Types of fires
According to the burning area, all fire classes are divided into extending and not
pervasive. In addition, they can vary in size of material damage and be massive, for example, in the forest, in large industrial enterprises and warehouses with combustible materials, as well as in settlements. Individual fires occur in a certain area, while continuous fires cover a large number of structures and are characterized by intense burning. In the absence of wind, such an element can develop into a fire storm, which is characterized by the formation of a giant turbulent column of flame, which moves at high speed.
Air exchange and fire load
Classes of fire regulated by ventilation are characterized by a limited oxygen content in the room with a simultaneous excess of combustible materials and substances. In this case, the spread of fire depends on the area of the supply openings or the flow rate of air that enters through mechanical ventilation systems. If there is an excess of oxygen in the room, the combustion process will completely depend on the fire load. In terms of their parameters, such fire classes are very similar to raging fire in open space.
Volumetric and local fires
In a volumetric fire, which is regulated by ventilation, intense
thermal effects on fences. Such combustion is characterized by the presence of a gas layer between the flame torch and the surface of the fencing. Moreover, the whole process is accompanied by an excess of oxygen. When regulating
fire with a fire load, a smoke screen is usually absent.
Classes of fire occurring locally are characterized by a small thermal effect on the surrounding fence. Their development depends on excess air, a variety of combustible materials and substances, as well as their condition and location in this room. It should be noted that volumetric fires, regardless of their enclosure, are called open, and local fires are closed, since they occur when the window and door openings are closed.