Acceptable fire risk. On the normative significance of individual fire risk

Individual risk is defined as the probability of occurrence of hazardous fire factors (HFP) during an accident at a certain point in space. Characterizes the distribution of risk. Social risk is assessed by the injury of at least 10 people and represents the dependence of the probability of occurrence of events consisting in the defeat of a certain number of people exposed to general physical injury on the number of these people, and characterizes the scale of fire and explosion hazard.

The fire safety of the technological process is considered unconditionally satisfied if:

individual risk is less than 10 -8;

social risk is less than 10 -7.

The operation of technical processes is unacceptable if the individual risk is > 10 -6 and the social risk is > 10 -5.

16. Fire hazard assessment of conventional technological processes

Fire Hazard Assessment of Conventional Processes(not increased fire danger) is somewhat different from that discussed earlier.

Fire Hazard Analysis such technological processes should include:

determination of fire hazard of substances used in the technological process;

determination of places where flammable materials are concentrated or the formation of flammable mixtures, gas-vapor-air mixtures is possible;

identification of possible ignition sources;

assessment of accident options and fire spread paths;

definition of fire prevention systems;

development of measures to improve fire safety of technological processes and its individual sections.

17. Measures to reduce the consequences of fires

To reduce the consequences of a fire The following activities are usually carried out:

limiting the spread of flammable liquid throughout the workshop or production area;

reducing the intensity of evaporation of flammable liquids;

emergency drainage of flammable liquids into a special container;

limiting the mass of hazardous substances during storage and in technological devices;

phlegmatization of flammable mixtures in apparatus;

removal of fire hazardous equipment to isolated rooms;

the use of devices to relieve pressure during the combustion of mixtures in apparatuses;

limiting the spread of fire using fire breaks and barriers;

use of fire extinguishing and fire alarm systems;

provision of access roads, fire tanks, etc.

18. Fire safety of buildings and structures

According to SNiP 21-01-97*, buildings must be provided with structural, space-planning and engineering solutions that provide in the event of a fire:

the possibility of evacuating people, regardless of their age and physical condition, outside to the territory adjacent to the building (hereinafter referred to as outside) before there is a threat to their life and health due to exposure to dangerous fire factors;

the possibility of saving people;

the possibility of access for personnel of fire departments and the supply of fire extinguishing means to the fire, as well as carrying out measures to save people and material assets;

non-propagation of fire to nearby buildings, including the collapse of a burning building;

limitation of direct and indirect material damage, including the contents of the building and the building itself, with an economically justified ratio of the amount of damage and the costs of fire prevention measures, fire protection and its technical equipment.

During operation you should:

ensure the maintenance of the building and the operability of its fire protection means in accordance with the requirements of the design and technical documentation for them;

ensure compliance with fire safety rules approved in accordance with the established procedure;

do not allow changes in design, space-planning and engineering solutions without a project developed in accordance with current standards and approved in the prescribed manner;

When carrying out repair work, do not allow the use of structures and materials that do not meet the requirements of current standards.

If permission for the construction of a building is obtained on the condition that the number of people in the building or in any part of it or the fire load is limited, notices of these restrictions must be posted inside the building in conspicuous places, and the building management must develop special organizational arrangements for fire prevention and evacuation people in a fire.

Based on statistical data, it is shown that the normative value of individual fire risk, regulated by the "Technical Regulations on Fire Safety Requirements", does not correspond to the level of development of the national economy, material and technical base, as well as the level of scientific and technical development of Russia.

In accordance with Art. 79 of the Federal Law, the individual fire risk in buildings, structures and structures should not exceed 10-6 per year when one (individual) person is located at the point furthest from the exit of the building, structure or structure.

Individual fire risk- fire risk, which can lead to the death of a person as a result of exposure to dangerous fire factors (Article 2, paragraph 9).

Fire risk- a measure of the possibility of realizing the fire danger of the protected object and its consequences for people and material assets (Article 2, paragraph 20).

Fire danger of the protected object- the state of the protected object, characterized by the possibility of the occurrence and development of a fire, as well as the impact of dangerous fire factors on people and property (Article 2, paragraph 22). Fire hazards (HFP) are listed in Art. 9 .

In table Table 1 presents the actual levels of individual fire risk for people (statistical data) in countries comparable in climate to Russia.

As follows from Art. 6, the main purpose of adopting technical regulations is to protect the life or health of citizens. In relation to ensuring fire safety, the Technical Regulations, taking into account the degree of risk of harm, should establish minimum necessary requirements to ensure fire safety.

Fire safety of the protected object- the state of the protected object, characterized by the ability to prevent the occurrence and development of a fire, as well as the impact of dangerous fire factors on people and property. From the table 1 it follows that even in the most developed countries, individual fire risks are many times higher than the standard value of individual fire risk provided for in Art. 79. Moreover, these risks in Finland, Norway and Sweden are considered acceptable by society and government agencies in these countries.

Table 1. Actual level of individual fire risk (statistical data) in countries comparable in climate to Russia

Probability of exposure* GPP per 1 person. per year R-10 6

* With a proportion of dead and injured from 0.8:1 to 1.3:1.

** Victims of the terrorist attack of September 11, 2001 are taken into account.

Acceptable fire risk- fire risk, the level of which is acceptable and justified based on socio-economic conditions (Article 2, paragraph 8). On this basis we can conclude: the requirement of Art. 79, which regulates the standard value of individual fire risk equal to 10 -6 per person. per year, and not sold in any of the countries indicated in the table. 1 cannot in any case be considered a minimum necessary requirement. The law does not formulate the concept of “minimum necessary requirement”. However, it does define the concept of “product safety”.

Safety of products, production processes, operation, storage, transportation, sales and disposal and (hereinafter - safety) - a state in which there is no unacceptable risk associated with harm to the life or health of citizens, property of individuals or legal entities, state or municipal property, the environment, life or health of animals and plants (Article 2).

The wording of the concept of “unacceptable risk” is also not given in the law, although the term “risk” is defined.

Risk- the likelihood of harm to the life or health of citizens, the property of individuals or legal entities, state or municipal property, the environment, the life or health of animals and plants, taking into account the severity of the harm.

The concept of “acceptable risk” is not provided for in the law, but the Technical Regulations provide a definition of the concept of “acceptable fire risk”, which is given above.

In table Table 2 presents the data necessary to calculate the correlation coefficient between individual fire risk and life expectancy in the USA (statistics are taken for the USA because for this country there are the most complete statistics regarding deaths and injuries in fires since 1913, when the individual fire risk was 15710 -6 per person per year with a life expectancy of 53 years).

Table 2. Data needed to calculate the correlation coefficient between individual fire risk and life expectancy in the United States

Correlation coefficient K between the values ​​given in columns 3 and 4 in table. 2, is:

Such a high value TO indicates that life expectancy and individual fire risk are characterized by an almost 100% (94%) correlation, which is inversely proportional: the lower the individual fire risk, the higher the life expectancy. The last one in Russia in 2011 was 66 years, and the individual fire risk was 18610 -6.

Thus, the actual individual fire risk in Russia was 186 times higher than the normative one provided for in Art. 79. Calculations have shown that an individual fire risk value of 10 -6 corresponds to the following life expectancy: in the USA - 81 years; in Russia - 86.4 years; in Finland, Norway and Sweden - 83-84 years.

Meanwhile, as follows from table. 3, the indicated life expectancy will be reached in some countries only after 35-40 years.

Table 3. Countries with the highest predicted life expectancy*

The training manual notes that “acceptable risk levels are established taking into account the actual accident rate (achieved safety level).” Based on the analysis of various types of risks, it was concluded that for Russia the value of an acceptable individual risk with a fatal outcome is 5010 -6 with the actual level of fire danger in 2010 86Т0 -6. This number represents the probability of exposure to dangerous fire factors per 1 people per year with a ratio of fatalities to injuries of 0.99:1 (see note to Table 1). Rounding this ratio to 1:1 and taking into account the acceptable individual risk of death (5010 -6), we come to the conclusion that the level of acceptability of individual fire risk in Russia currently does not exceed 10010 -6. Approximately the same level of individual fire risk was in 1941 in the United States (see Table 2), while life expectancy was 64 years. In Russia, in 2011, life expectancy was 66 years.

Conclusion

The standard value of individual fire risk, regulated by Art. 79, corresponds to a life expectancy of 83-86 years in Russia and in countries comparable in climate to Russia. Moreover, it does not correspond to the economic, social and cultural level of development of any country in the world. In accordance with Art. 3 of the law, one of the principles of technical regulation is its compliance with the level of development of the national economy, material and technical base, as well as the level of scientific and technical development. It is advisable to bring the normative value of individual fire risk into line with the level of development of the national economy, material and technical base, as well as with the level of fire-technical development of Russia. Analysis of the numerical values ​​of various types of individual risks of death in Russia, including individual fire risk, as well as comparison of the latter with individual fire risks in countries similar in climate to Russia, made it possible to justify the permissible (acceptable) individual fire risk in Russia at the level of 100 10 -6 or less per person. in year. It is advisable to recognize this value of individual fire risk as normative and, in the prescribed manner, add it to Art. 79 of the Technical Regulations corresponding amendments.

BIBLIOGRAPHY

1. Technical regulations on fire safety requirements: Federal. Law of July 22, 2008 No. 123-FZ; accepted by State Duma 07/04/2008; approved Sov. Federation 07/11/2008 - M.: FGU VNIIPO, 2008. - 157 p. // Russian newspaper. - 2008. - No. 163; Collection legislation of the Russian Federation. - 2008.-№30
2. Fire risks. Vol. 2: Dynamics of fire risks / Ed. N. N. Brushlinsky. - M.: FGU VNIIPO EMERCOM of Russia, 2005. - 82 p.
3. On technical regulation: Federal. Law of December 27, 2002 No. 184-FZ; accepted by State Duma 12/15/2002; approved Sov. Federation 12/18/2002 // Russian newspaper. - 2002. - No. 245
4. Fire risks. Dynamics, control, forecasting / Ed. N. N. Brushlinsky and Yu. N. Shebeko. - M.: FGU VNIIPO EMERCOM of Russia, 2007. - 370 p.
5. United Nations Demographic Yearbook 2001. United Nations. -New York, 2003. - 748 rub.
6. Vishnyakov Ya. D., Radaev N. N. General theory of risks: textbook. manual for university students.-2nd ed., revised. - M.: Publishing house. Center "Academy", 2008. - 368 p.

A. V. FIRSOV, senior lecturer of the department of civil protection of the State Fire Service Academy of the Ministry of Emergency Situations of the Russian Federation, Moscow, Russia

E. V. KRYUKOV, Ph.D. military Sciences, Associate Professor, Deputy Head of the Department of Civil Defense of the State Fire Service Academy of the Ministry of Emergency Situations of the Russian Federation, Moscow, Russia

G. X. KHARISOV, Doctor of Engineering. Sciences, Professor of the Department of Civil Protection of the State Fire Service Academy of the Ministry of Emergency Situations of the Russian Federation, Moscow, Russia

Article provided by the editors of the magazine "Fire and Explosion Safety" ( http://www.firepress.ru)

Figure 6.1 - Procedure for calculating individual fire risk

I. GENERAL PROVISIONS

EXERCISE 1

Subject:« Calculation of fire risk in buildings, structures and structures of various classes of functional fire hazard»

An independent fire risk assessment (Fire Safety Audit) is a business activity carried out by relevant entities to assess compliance with established requirements of fire safety systems at protection facilities.

Carried out in accordance with the Decree of the Government of the Russian Federation dated 04/07/2009 No. 304 “On approval of the Rules for assessing the compliance of protected objects (products) with established fire safety requirements through an independent fire risk assessment.”

The results of an independent fire risk assessment are formalized in the form of a conclusion, in which, in cases established by the Federal Law “Technical Regulations on Fire Safety Requirements,” fire risk assessment calculations are carried out.

Fire risk- a measure of the possibility of realizing the fire danger of the protected object and its consequences for people and material assets.

Individual fire risk- fire risk, which can lead to death as a result of exposure to hazardous fire factors (HFP).

Acceptable fire risk- fire risk, the level of which is acceptable and justified based on socio-economic conditions.

The magnitude of individual fire risk is primarily ensured by the fire prevention system and a set of organizational and technical measures.

Fire risk calculation- assessment of the impact of general physical injuries on people and the measures taken to reduce the frequency of their occurrence and their consequences.

Calculations for assessing fire risk are made in accordance with Resolution No. 272 ​​of March 31, 2009 “On the procedure for carrying out calculations for assessing fire risk” by comparing the calculated values ​​of fire risk with the corresponding standard values ​​of fire risks established by the Federal Law “Technical Regulations on Fire Safety Requirements” "

Fire risk assessment calculations are an integral part of the fire safety declaration or industrial safety declaration. Determination of estimated fire risk values ​​is carried out on the basis of:

A) Analysis of the fire hazard of the protected object.

To do this, collect data about the object of protection:

Space planning solutions, including evacuation plans;

Thermophysical characteristics of enclosing structures and installed equipment;

Type, quantity and placement of flammable substances and materials;

Number and locations of likely placement of people;

Fire alarm and fire extinguishing systems, smoke protection, fire warning and evacuation control systems.

B) Determining the frequency of fire hazardous situations.

C) Construction of fields of fire hazards for various scenarios of its development.

D) Assessment of the consequences of exposure to dangerous fire factors on people for various scenarios of its development.

D) Availability of fire safety warning systems for buildings, structures and structures.

1. An individual fire risk meets the requirement if:

Where Q c - calculated value of individual fire risk;

Standard value of individual fire risk, year.

2. Estimated value of individual fire risk Q V for each building is calculated by the formula :

Q in = Q p(1 - R a p) P pr (1 ​​- P e) (1 - P pe)

Where Q n - the frequency of fire occurrence during the year, determined on the basis of statistical data (Appendix No. 1); in the absence of statistical data, it is allowed to accept Q n = 4 ? 10 -2 for each building;

R a p - the probability of effective operation of automatic fire extinguishing systems AUPT), is accepted according to technical documentation, and in the absence of information it is allowed to accept R an = 0.9;

P pr - the probability of the presence of people in the building, determined by the formula:

R pr = t func/24,

Where t functional - time of people staying in the building, hours;

P pe - probability of effective operation of fire protection systems;

R e - probability of evacuation of people, calculated according to the dependence:

where t r is the estimated time for evacuation of people, min. Determined based on modeling the movement of people before going outside (in one of three ways);

t ne - evacuation start time (time interval from the outbreak of a fire to the start of evacuation of people), min. the value of the start time of evacuation, tne, for the location of the fire should be taken equal to 0.5 min; for buildings not equipped with a warning and evacuation control system, depending on the functional fire hazard class and the characteristics of the population tne = 6-9 min; for buildings equipped with a warning and control system for people, depending on their types, as well as the functional hazard class and characteristics of the population t ne = 1-6 min.

Fire Hazardous Factors (HFP)- fire factors, the impact of which can lead to injury, poisoning or death of a person and material damage.

tbl - time from the start of the fire to the blocking of evacuation routes as a result of the spread of general physical properties on them, which have maximum permissible values ​​for people (time of blocking of evacuation routes), min. Determined by calculation, which is based on the calculation of the time of formation of the general physical phase.

The maximum permissible values ​​for each of the fire hazards are:

Temperature: 70°C;

By heat flow - 1400 W/m2;

For loss of visibility - 20 m;

For reduced oxygen content - 0.226 kg?m;

For each toxic gaseous combustion product
(CO 2 - 0.11 kg?m -3; CO - 1.16?10 -3 kg?m -3;HCl - 23?10 -6 kg?m -3).

The critical time for each of the dangerous fire factors is defined as the time this factor reaches the maximum permissible value along the escape routes at a height of 1.7 m from the floor.

3. Blocking time is determined t bl from the ratio:

Fire- uncontrolled combustion causing material damage, harm to life and health, and the interests of society and the state.

Evacuation - the process of organized independent movement of people directly outside or a safe zone from premises in which there is a possibility of exposure to dangerous fire factors.

Critical fire duration- the time during which the maximum permissible value of the fire hazard factor is reached in the established mode of its change.

Fire hazards, affecting people and material values ​​are:

Flames and sparks;

Heat flow;

Increased ambient temperature;

Increased concentration of toxic products of combustion and thermal decomposition;

Reduced visibility in smoke;

Reduced oxygen concentration.

Associated manifestations of general physical injury include: fragments and parts of collapsed buildings and equipment; radioactive and toxic substances and materials from destroyed installations; high voltage removal; explosion hazards and exposure to fire extinguishing agents.

Maximum permissible value of fire hazard factor- this is the value of a hazardous factor, the impact of which on a person during the critical duration of the fire does not lead to injury, illness or deviation in health status within a normatively established time, and the impact on material assets does not lead to a loss of stability of the object during a fire.

Object stability in case of fire- the property of an object to prevent the impact on people and material assets of fire hazards and their secondary manifestations.

An indicator of the level of fire safety of people at facilities is the absence of a threat to their lives from dangerous fire factors. It is achieved (determined) by the required time for evacuation of people from the building (facility), i.e. time of blocking (tbl) of evacuation routes by one of the physical safety points.

The required evacuation time is calculated as the product of the fire duration critical for humans and the safety factor. It is assumed that each hazardous factor affects a person independently of the others.

The calculation of the required evacuation time is made for the most dangerous scenario of fire development, characterized by the highest rate of increase in dangerous fire factors in the room (building) in question. In this case, the values ​​of the critical duration of the fire are first calculated based on the condition that each of the physical characteristics reaches the maximum permissible values ​​in the area where people are present:

For elevated temperature:

By loss of visibility

According to reduced oxygen content:

For each toxic combustion gas:

where B - dimensional complex depending on the heat of combustion of the material and the free volume of the room, kg;

A is a dimensional parameter that takes into account the specific mass burnout rate of combustible material and the fire area, kg/s;

Initial air temperature in the room, °C;

P- exponent taking into account the change in the mass of burnt material over time;

Z is a dimensionless parameter that takes into account the uneven distribution of physical permeability along the height of the room;

Lower heat of combustion of the material, MJ/kg; the value of the lower calorific value of the material is taken from reference literature;

S p - specific isobaric heat capacity of gas, MJ/kg × K; the value of the specific isobaric heat capacity of the gas is taken from reference literature;

φ - heat loss coefficient; depending on the conditions of interaction of the combustion zone with the environment, the value of the heat loss coefficient ranges from 0.4 to 1.0;

η - coefficient of combustion completeness, depending on the type of combustible material and external conditions of the combustion process, the value of the combustion completeness coefficient ranges from 0.75 to 0.93;

V- free volume of the room, m 3 ; the free volume of the room corresponds to the difference between the geometric volume and the volume of equipment or objects located inside. If it is impossible to calculate the free volume, it is allowed to take it equal to 80% of the geometric volume;

a is the reflection coefficient of objects on escape routes; in the absence of special requirements, the value of α is taken equal to 0.3;

E - initial illumination, lux: in the absence of special requirements, value E taken equal to 50 lux;

- maximum visibility range in smoke, m; in the absence of special requirements, the value is taken equal to 20 m;

D m - smoke-forming ability of burning material, Np?m 2 /kg; the value of the smoke-forming ability of a burning material is taken from reference literature;

L- specific release of toxic gases during combustion of 1 kg of material, kg/kg; the value of the specific yield of toxic gases during combustion of 1 kg of material is taken from the reference literature for each of the gaseous toxic combustion products;

X- maximum permissible content of toxic gas in the room, kg×m -3;

L O2 - specific oxygen consumption, kg/kg; the value of the specific oxygen consumption required for combustion of 1 kg of a substance or material is taken from reference literature.

If the sign of the logarithm turns out to be a negative number, then this GPP is not dangerous.

Parameter Z calculated by the formula:

Where h- height of the working area, m; N - room height, m.

The height of the working area is determined by the formula:

Where - height of the platform on which people are located above the floor of the room, m;

- difference in floor heights equal to zero when it is horizontal, m.

People at higher elevations are at greatest risk in a fire. Parameters A and n calculate:

Where b- perpendicular to the direction of flame movement, size of the combustion zone, m.

From the values ​​of the critical fire duration obtained as a result of calculations, the minimum is selected:

The required evacuation time, min, from the premises in question is calculated using the formula:

When people are located on sites of different heights, the required evacuation time should be determined for each site.

4. The estimated evacuation time t p is determined

The estimated time for evacuation of people from premises and buildings is established by calculating the time of movement of one or several flows through emergency exits from the most remote places where people are located.

When calculating, the entire path of movement of the human flow is divided into sections (passage, corridor, doorway, flight of stairs, vestibule) of length l i and width δ i. The initial sections are passages between workstations, equipment, rows of seats, etc.

When determining the estimated time, the length and width of each section of the evacuation route are taken according to the design. The length of the path along flights of stairs, as well as along ramps, is measured along the length of the flight. The path length in the doorway is assumed to be zero. An opening located in a wall more than 0.7 m thick, as well as a vestibule, should be considered an independent section of a horizontal track having a finite length.

The estimated time for evacuation of people should be determined as the sum of the time of movement of the human flow along individual sections of the route according to the formula:

where is the time of movement of the human flow in the first (initial) section, min; - time of movement of the human flow on each of the sections following the first section of the route, minutes;

Time interval from the outbreak of a fire to the start of evacuation of people min.

The time it takes for the flow of people to move along the first section of the route, min., is calculated using the formula:

Where - length of the first section of the path, m;

- the value of the speed of movement of the human flow along a horizontal path in the first section is determined according to table 6.1 depending on the density of the human flow D, m/min.

“Technical Regulations on Fire Safety Requirements”, the requirements for ensuring the fire safety system of protected facilities have become more stringent.

Federal law introduced the concept fire risk, by which we mean the real possibility of fire danger for objects with the definition of negative consequences from the impact of fire in relation to material assets and people.

Fire risk assessment is carried out by specialists on the basis of the project “Procedure for conducting fire risk assessment for public facilities” developed by VNIIPO EMERCOM of Russia. This document allows you to use in each specific case your own method for calculating the time required to evacuate the object as a whole and for the movement of the mass of people evacuated from the danger zone.

The assessment process determines the level of compliance with the necessary fire safety requirements of each protected facility. Protected objects include objects of production (industrial and agricultural, engineering and transport, etc.) and non-production purposes (service and education, healthcare and culture, residential buildings).

Each protected object for which the law provides for the calculation of fire risks is required to have a fire safety declaration. In this case, a fire risk assessment is mandatory. If fire safety is not regulated by special laws for any security facilities, a fire risk assessment is carried out specifically to justify the need to ensure fire safety at such facilities.

Fire risks are divided into:

• acceptable,
• individual (consequence in the form of human death),
• social (the risk of death of an entire group of people as a result of a fire).

What is included in a fire risk assessment? First of all, the calculated values ​​of fire risk at a specific protection object are determined, and then compared with the fire risk standards already established by Federal Law. This calculated value is recognized as a quantitative measure of the probability of a fire situation at the facility and the consequences that are possible as a result of a fire for others.

The risk of fire consequences in the form of loss of life is a quantitative measure of the possible realization of a fire hazard, primarily at a production facility. The death of its personnel and even people living in areas adjacent to the facility, the safety of which directly depends on the fire safety system of the facility, is possible.

Hence the classification of fire risks into individual and social. With an individual risk, its value for an employee of the facility’s personnel is calculated by the frequency of injury to the employee during the year by dangerous fire factors. In this case, the presence of the employee in all buildings and premises located on the territory of this facility is taken into account.

Social risk is determined by the frequency of fire situations, as a result of which groups of at least 10 people may suffer.

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The assessment of individual and social risk for buildings of industrial enterprises should be carried out in accordance with GOST R 12.3.047-98.

The assessment of potential, individual, social and collective risks for the territory of the enterprise should be carried out according to the methods outlined below.

Potential risk.

Potential fire risk– frequency of occurrence of fire hazards at the considered point in the territory.

The potential risk does not depend on the number of workers at the enterprise and their location throughout the facility, but is determined solely by the technology used and the reliability of the equipment used. Potential risk is used as a criterion for the acceptability of fire danger for the population, for which the magnitudes of potential and individual risks are assumed to be equal.

Magnitude of potential risk R(a)(year -1) at a certain point in the area A, where the enterprise is located, is determined using the ratio:

I- number of accident development scenarios (branches of the logical tree of events of occurrence and development of the accident);

Qdi(a)– conditional probability of hitting a person at a certain point in the area, A as a result of implementation i the th accident development scenario corresponding to a specific accident-initiating event;

Q(A i)- frequency of sales throughout the year i-scenario of accident development, year -1.

Conditional probabilities of human injury Qdi(a) are determined by the values ​​of probit functions.

Magnitude P(a) is determined by overlaying affected zones by hazardous factors, taking into account the frequency of each accident development scenario, on a map of the area, linking them to the corresponding accident-initiating event (equipment element, technological installation) and the orientation of the affected area in accordance with meteorological conditions (for jet combustion, flash fire, formation and explosive transformation of a gas-vapor-air cloud). When calculating risk, various meteorological conditions with typical wind directions and expected frequency of their occurrence are considered.

The risk calculation procedure involves consideration of various emergency situations and determination of zones affected by dangerous factors of fire and explosion, and the frequency of their occurrence. For the convenience of calculations, the territory of the area is divided into zones, within which the values P(a) are assumed to be the same.

If necessary, the assessment of the conditional probability of injury to a person is carried out taking into account the combined impact of more than one hazardous factor (for branches with stages with the transition condition “I”). So, for example, to calculate the conditional probability of injury to a person in the implementation of an accident scenario associated with the explosion of a tank with flammable liquid under pressure located in the fire, it is necessary to take into account, in addition to the thermal radiation of the fireball, the impact of the shock wave and fragments.

Conditional probability of human injury Qdi(a) from joint independent impact of several hazardous factors as a result of implementation i- accident development scenario is determined as follows:

(14)

h- number of considered hazardous factors of the accident;

Q k- probability of implementation k th dangerous factor;

Q dik (a)- conditional probability of defeat k th dangerous factor.

The results of potential risk calculations are displayed on the map (situational plan) of the enterprise and surrounding areas in the form of closed lines of equal values ​​(isolines of the function R(a)).

Function isolines R(a) are called risk contours. Their physical meaning is that they divide the territory of the enterprise (as well as the area around the enterprise) into areas in which the expected frequency of occurrence of hazardous accident factors leading to death is within certain limits indicated in the figure.

The contours of the risk do not depend on the number of employees at the enterprise or their job responsibilities, but are determined solely by the technology used and the reliability of the equipment used. Potential risk is used as a measure (acceptability/inacceptability criterion) of the fire safety level of an object.

Individual risk.

Individual fire risk– the frequency of injury to an individual as a result of exposure to the fire hazards under study.

Individual risk is used as a criterion for the admissibility of fire danger for workers of a particular profession. Individual risk takes into account the time spent by a particular category of workers in a hazardous area with high potential risk values.

For any employee of an enterprise, there is a possibility of death in the event of an accident. The loss of life during a certain period of time (year) is a random event, depending on the type of professional activity, including the duration of the worker’s stay in areas that meet different risk contours when he moves around the industrial site of the enterprise during a work shift.

For the purposes of personnel safety management, a quantitative measure of the occurrence of this random event is used - the frequency of injury to a certain person by dangerous factors of fire (explosion), called individual risk.

Thus, individual risk is defined as the expected frequency of injury to a certain employee of an enterprise by hazardous accident factors during the year.

The areas into which the territory of the enterprise is divided are designated:

J, j = 1, … J.

For the convenience of describing calculations, employees of the enterprise are numbered:

m = 1, …, M.

Current employee number m, unambiguously determines the name of the employee’s position, his category and other features of his professional activity necessary for assessing safety.

Amount of individual risk Rm(year -1), for an enterprise employee m, is determined using the relation:

, (15)

Р(j)– the magnitude of the potential risk in j th region of the enterprise territory, year -1;

q jm– the proportion of time during which an employee of the enterprise m is in j-th region of the enterprise territory.

The proportion of time during which an employee is in a certain area of ​​the enterprise territory is calculated based on decisions regarding the organization of operation and maintenance of equipment.

Social risk.

Social fire risk– dependence of the frequency of occurrence of events in which at a certain level at least a certain number of people were affected, on the number of victims.

Social risk characterizes the severity of the consequences (catastrophicity) of a fire. In practice, social risk is most often assessed by the injury of at least 10 people.

To analyze the impact of industrial accidents on people, as well as to establish the acceptability of a particular level of fire or industrial safety, the concept of social risk is used.

Social risk is specified using a function whose values ​​are values ​​that determine that at least a certain number of people died in a fire accident.

Social risk S(year -1) is determined by the formula:

L- number of accident scenarios for which the condition is met
N i ³ N 0;

N i– expected number of deaths as a result of implementation i- accident development scenario;

N 0- the number of deaths for which the magnitude of social risk is assessed. This document accepts N 0 = 10.

Expected death toll as a result of implementation i-scenario of accident development can be estimated using the following formula:

, (17)

J- the number of areas into which the territory of the enterprise and the territory adjacent to the enterprise is divided ( j – area number);

Q dij- conditional probability of injury to a person in j region, dangerous factors of fire (explosion) during the implementation i- accident development scenario;

n j- average number of people in j-th region.

Social risk S is an integral quantity. At the same time, social risk can also be considered as a vector quantity, the components of which have the dimension of year -1. In this case, the results of social risk calculations can be presented in the form of so-called F/N diagrams, where the horizontal axis is plotted N- number of deaths as a result of implementation i- state scenario for the development of the accident, and along the vertical axis - F- frequency of scenario implementation in which at least at least N Human. Such dependencies can be approximated by a curve-graph with a continuous function F(N). In this case, the above value S is described by the following expression:

Collective risk.

For the enterprise personnel as a whole, there is a non-zero probability of death of some workers in the event of an accident.

The number of deaths during a certain period of time (year) is a random variable, depending on the danger of production, the number of workers and a number of other factors.

For the purposes of personnel safety management, the mathematical expectation of this random variable is used. This characteristic is called the collective risk of personnel from accidents.

The magnitude of the collective risk of personnel WITH(person×year -1) is determined using the ratio:

. (19)

The connection between the individual risk of an employee from accidents R m and the collective risk of personnel from accidents establishes a relationship.