Task 1.1. Assess risk and its acceptable levels for high-risk facilities.

In accordance with Law of Ukraine “On High-Risk Facilities” the high-risk facility is a facility where one or more dangerous chemicals are used, created, produced or stored or transported in amounts which are equal to or higher than normative limits, and also other facility which causes hazard of development of natural and/or technogenic emergencies.

The Methodology specifies the order of hazard’s analysis and risk assessment of high-risk facilities, levels and criteria of acceptable risks.

The Methodology identifies three types of risk: individual, societal and territorial.

Individual risk is the probability of the human mortality, injuries or other dangerous consequences of the hazards taking into account probability of the person’s location near the source of hazard.

Societal risk is the probability of human mortality, injuries or other dangerous consequences over defined quantity taking into account probability of the person location near the source of hazard.

Territorial risk is the probability of mortality, injuries or other dangerous consequences for the person located in a certain place during a year.

In accordance with the Methodology the analysis of hazard and risk of accidents at high-risk facilities includes the following stages:

1. Definition of hazard analysis and risk assessment;

2. Analysis of hazard and conditions of accidents development;

3. Risk assessment (RA) of accident;

4. Analysis of conditions and assessment of accident probability;

5. Definition of accidents scale and their consequences;

6. Assessment of the probability of accident consequences;

7. Assessment of the acceptable risk levels;

8. Risk management.

Stage 1. Definition of hazards includes the following stages:

- definition of task and goals of risk analysis;

- identification of high-risk facilities and risk analysis (identification of hazard is the definition of the hazard type and its properties for development of prevention and protection measures);

- determination of the objects of social concern for risk assessment.

Targets of the risk analysis are the following:

- assessment of risk level caused by operation of high-risk facility;

- risk management by comparison of acceptable levels of risk and decision-making for its decreasing.

The main object of social concern is a human. It is necessary to define the level of hazard for an individual. The places of residence of individuals and other objects of concern, like enterprises and organizations concentrated in the damage area, should be located and marked on the map.

As other objects of concern the socially significant facilities, elements of ecosystems, public and personal property should be considered. It is also important to consider sites with large concentrations of people, elements of environment, recreation areas, cultural sites, critical public infrastructures and locations of public authorities etc.

Taxonomy of hazards. Hazards are classified depending on origin, area of realization, localization, size of damage, consequences, time of realization, structure, and type of impact on human body.

Lots of potential hazards exist and surround us all the time. Certain conditions are needed to transform these potential hazards into realized. These conditions are the coincidence of time, space and hazard, and lack of protection means (Fig.1.1).

Fig.1.1. Hazard taxonomy

Depending on the origin all hazards are subdivided into four main groups: natural (volcanic eruptions), technogenic (transport accidents), socio-political (wars, revolutions) and complex. Complex hazards include the majority of hazards on the Earth: techno-natural (for example, greenhouse gases and all other environmental protection problems), techno-social (occupational diseases) and socio-natural (flu or HIV epidemics, alcohol abuse).

And when some of these hazards transform into realized, we get emergencies, accidents, catastrophes, natural disasters, deaths and diseases.

In accordance with the Code of Civil Protection of Ukraine (2012) the emergency is a situation in a certain area or with a subject of economic activity, or at water bodies, which is characterized by malfunction of normal human activities caused by the catastrophes, epidemic, epizootic, epiphytotic, using of destruction means, or other dangerous event which may lead (or has led) to development of health and life-threatening hazards, huge number of dead and injured persons, material losses, and also lead to impossibility of residence in the territory, economic activity.

Accident is a dangerous event of technogenic origin which causes damaging, injuring of civilians or development of hazards to life and health within the certain territory or territory of the subject of economic activity, leads to destruction of homes, buildings, equipment and transport vehicles, malfuncting of manufacturing or transportation process, and gives rise to above-standard or breakdown escapes of pollutants and other harmful impact on environment.

Catastrophe is huge scale accident or other event, which causes dangerous consequences.

Natural disaster is a natural phenomenon which has a huge destructive power, causes harm to territory, where it develops, troubles normal human activities and leads to economic losses.

Stage 2. Analysis of hazards and conditions of accidents’ development is made only for hazards connected with the disturbance of safe operation of facilities. The technological environment and presence in this environment of hazardous substances, their physicochemical, chemical and thermal-physical and other properties should be analyzed.

The operation regimes and deviations in technological system, which may cause dangerous conditions, should be defined. Based on the deviation analysis the dangerous events that have led to accidents are identified. The list of such events that have led to dangerous events should be made.

For operation safety analysis the following analysis of techniques may be used:

- “what if-?”;

- check list;

- operation hazard analysis

- and other techniques cited in scientific or regulatory literature.

Stage 3. The assessment of the accident probability during one year is performed for the RA of accident caused by certain triggering event.

RA is the determination of quantitative or qualitative value of risk related to a defined situation and a recognized hazard.

Quantitativeapproaches to RA are the following: engineering, modelling, expert and sociological:

- RA engineering is based on statistical information, prediction of danger probabilities, creation of events-trees;

- RA modeling is based on creation of models of hazard impact on a human, a social group, humanity;

- RA expert uses the probabilities of events defined by experts;

- RA sociological includes opinion surveys of citizens.

All these approaches perform best in their combination, but the main is engineering one. Generally, the formula for risk assessment is the following:

(1.1)

n denotes quantity of dangerous events (accidents or injuries);

N denotes maximum, theoretically possible quantity of dangerous events,

D is losses per accident;

k_i are the coefficients which include changes of initial conditions.

The following techniques may be used during analysis of possible deviations:

- fault trees;

- analysis of types and outcomes of faults;

- statistical data processing activities concerning accident rate of a technological system which correspond to specifics of high-risk facility;

- and other valid techniques.

If the probability of accidents is unacceptable then the approaches for its reduction should be found.

For assessment of territorial risk based on obtained levels (during accident modelling) of damaging factors in k point of space the relative probability (P_ck) of the fatal outcome for individual should be performed.

Territorial risk in point k of the space for the triggering event in a certain sourse of danger taking into account the probable or realised results of accident is equal to:

, (1.2)

where P_ck denotes the conditional probability of the lethal outcome in the point k;

P_af is the conditional probability of realization of the certain type of accidents (fires, explosions etc.);

P_bij is the conditional probability of accident in the sourse number i under realization of lethal outcome j;

P_UM is the conditional probability of one of the possible accident outcomes.

There are a lot of probable outcomes for every triggering event, identified during the process of hazard analysis. For every element of the technological system the quantity of triggering events is unlimited and dependent on types of hazards and places of occurrence.

If the probability of person’s appearance in point k is known as P_i^k, then we are able to assess individual risk of the person’s death which lives in this point:

, (1.3)

where P_t^k denotes total territorial risk in point k;

P_n^k denotes the probability of person’s appearance in point k.

Based on the levels of territorial risk in the certain region and population density the anticipated number of dead persons can be assessed during 1 year (societal risk) , or the possibility of dying in the region during the year, which exceeds 10 persons R_S caused by possible accidents at high-risk facility.

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