External fires are those in which signs of burning (flame, smoke) can be set visually. Such fires occur during the burning of buildings and their structures, stacks of sawn timber, coal, peat and other material valuables located in open storage areas; when burning petroleum products in tanks, in open process plants and racks; forests, peat fields, grain crops, etc. Outdoor fires are always open.
Internal fires are those that arise and develop inside buildings. They can be open and hidden.
In case of open fires, signs of burning can be established by inspecting the premises (for example, when burning property in buildings for various purposes; equipment and materials in production shops; partitions, floors, coatings, etc.).
In case of hidden fires, combustion takes place in the voids of building structures, ventilation shafts and channels inside the peat deposit. Signs of combustion in this case are the exit of smoke through the cracks, a change in the color of the plaster, and the heating of the structures. Fire can be seen, as a rule, when opening or dismantling stacks and structures.
With a change in the situation, the type of fire may change. So, with the development of a fire in a building, hidden internal combustion can go into open internal, and then internal into external, and vice versa.
Fires at industrial enterprises and in settlements can be separate (in a building or structure) and massive, representing a set of individual fires and covering significant territories.
Examples can be given from literary sources, newspapers, radio and television.