Principles of fire risk calculation.
Principles of fire risk calculation.
The first attempts in this area were the adoption of GOST 12.1.004 «Fire Safety. General Requirements» and SNiP 21-01-97 «Fire Safety of Buildings and Structures». The state standard, for the first time, introduced the concept of «probability of exposure to hazardous fire factors on people» and provided a calculation methodology, which led to the possibility of influencing such probability using engineering methods. SNiP 21-01-97 allows the possibility of using calculation scenarios based on the relationship between the time parameters of the development and spread of hazardous fire factors, evacuation of people and fire fighting when developing fire safety measures.
Further development of these principles occurred with the adoption of the federal laws «On technical regulation» and «Technical regulations on fire safety requirements». The latter of these laws introduced the concept of fire risk as «a measure of the possibility of the implementation of a fire hazard of a protected object and its consequences on people and material assets». In this case, the fire hazard of a protected object is understood as a state characterized by the possibility of the occurrence and development of a fire, as well as the impact of dangerous fire factors on people and material assets.
Thus, the modern legislative base allows, by correlating possible losses from fires, fire risk assessments, with the costs of the fire safety system, to formulate the optimal composition of fire prevention measures.
Quantitative methods for assessing fire risk can be divided into four groups:
- point schemes,
- logical trees,
- statistical models,
- mathematical models.
The point scheme method received its greatest distribution after the development of a method for assessing the fire hazard of industrial, residential and public buildings by an employee of the Swiss Fire Prevention Association, M. Gretener. In one modification or another, Gretener's method is widely used in European countries (Austria, Spain, France, Belgium, the Netherlands) and the USA.
Gretener's method involves taking into account the quantitative characteristics of factors, the presence of which in a building increases its fire hazard, and on the other hand, elements of the fire safety system that reduce its fire hazard. The quantitative values of the factors taken into account in the point scheme method are established by experts.
The Gretener method can be used to obtain dimensionless fire risk assessments for the purposes of ranking various objects by fire hazard level, but it does not allow obtaining absolute values of fire losses, suitable, for example, for economic analysis of fire hazard.
The unconditional advantage of the point scheme method is the ability to take into account a large number of factors influencing the condition of the object and its fire hazard when assessing fire risk.
The Research Institute of Fire Safety of the All-Russian Fire Safety Organization is developing a modified method for point assessments of fire risk, taking into account the developments of domestic scientists in the field of quantitative assessment of the level of fire hazard of buildings and structures.
The method is based on the relationship between the fire risk PR and the product of the probability of a fire and its development QB by the amount of expected losses Цпот:
ПР=ОВхЦпот
When calculating the QB value, the main characteristics of the building and its architectural and planning solutions are taken into account: dimensions, number of storeys, size of fire gaps from neighbouring buildings, etc.; presence and condition of passive systems (installation of fire compartments, use of low-fire hazard materials, fire-resistant structures, fire protection equipment; presence and length of evacuation routes); presence and technical condition of active fire protection systems (fire alarm, fire alarm, smoke removal, primary fire extinguishing equipment, fire water supply, automatic fire extinguishing systems, etc.). In addition, when assessing the probability of occurrence and development of a fire, the presence of people in the building, the degree of fire and explosion hazard of the equipment and technological processes used and other factors are taken into account.
Significant difficulties are encountered in assessing expected losses from fires. In accordance with the definition of fire risk contained in the Federal Law, this value must include the impact of hazardous fire factors on people and material assets. Losses from fires of material assets can be calculated with a fairly high accuracy. In this case, mathematical methods for predicting the development of a fire are used, allowing us to obtain time characteristics of the development of a fire and the accompanying hazardous factors in a building. Losses from the loss of life and the reduction of their performance at present (in general) cannot be quantitatively assessed. It seems appropriate to use the experience of foreign countries when solving such issues.
Source A. Ya, Korolchenko, Doctor of Technical Sciences, Professor, Deputy Director for Science, Research Institute of VDPO