Best Practice Guide

Contemporary state of the scientific knowledge about human factors and labour safety in Slovakia

This guide was prepared by

Ludovit Jelemensky

Department of Chemical and Biochemical Engineering

STU Bratislava

Slovakia

PRISM – the human factors network

for the process industries

Objective“the improvement of safety in the European process industries through raising awareness of, and sharing experience in, the application of human factors approaches and stimulate their development and improvement to address industry-relevant problems in batch and continuous process industries.”

The PRISM Thematic Network was established in 2001 with financial support from the European Union, DG Research, with the aim of creating an extensive forum within which industry, universities, research centres and practitioners could collaborate to improve the flow of fundamental knowledge and practical experience in human factors and identify areas for improvement by collaborative effort.

All of the deliverables of the Network have been tailored to provide practical guidance on good human factors practices as an aid for the process industries.

StructureThe work of the Network was split into 4 Focus Groups:WP 1 Cultural and organisational factorsWP 2 Optimising human performanceWP 3 Human factors in high demand situationsWP 4 Human factors as part of the engineering design process

The Focus Groups have produced a number of reports and guides as well as leading a series of seminars aimed at facilitating knowledge interchange between Network members; evaluating current experiences in the application of human factors; identifying where new or improved tools or guidance are needed by the process industries, with

particular emphasis on the needs of SMEs, and publish such guidance; and

Each Focus Group was led by a Co-ordinating Partner who co-ordinated the activities, fostered links to end-users, carried out specific tasks and ensured completion of agreed deliverables. Co-ordinating Partners worked closely with an End-user representative who acted in an advisory capacity. All End-user advisors were drawn from EPSC membership and were representatives of manufacturing process industries. This structure has helped to ensure that the activities of the Network were focused on the needs of the process industries.

More information can be obtained from the PRISM website www.prism-network.org

Legal framework

The directive of the EU Council 89/391/EEC about measures aimed at increasing safety and

health protection of workforces at their workplace attempt the employers to identify and assess

risks threatening the safety and health of employees, and determine and carry out necessary

measures. Furthermore, in planning risk prevention the influence of technique, labor

organization, working conditions, social relations and the environment on the workplace should

be taken into account. A similar approach has the Slovak legislature incorporated in the law of

the National Council of the SR No.330/1996 Collection of Laws concerning the Labor Safety and

Health Protection.

Currently the implementation of legal measures in injuries prevention has still been

oriented on technical and technological areas, and/or labor organization rather than on the

understanding of human factors. In contradiction with calculable engineering quantities in

designing production plants the requirements concerning human behavior and activities are given

in such way that they cover the existing risks regardless to the fact whether these demands can be

fulfilled or not. Just the human error of the employees and/or the failure of human factors are the

most common cause of labor injuries according to statistics. In comparison with direct causal

relations between the cause and consequence, which appear in the majority of cases of technical

character, in the investigation and study of human factors simple causal relations cannot be

applied.

Reliability of the operator’s performance

The reliability of a facility can be defined, in accordance with J. Stikar, J. Hoskovec and M.

Stríženec (1982), as an ability to maintain its functional properties within the given range of

deviations from the indicators of quality at particular operation conditions (work environments,

service, feeding) in the lifetime of the equipment and within the range of operation faults not

exceeding an acceptable limit. Thus, the reliability is a property to fulfill the required tasks within

the given period at given working conditions. The reliability of an arbitrary system corresponds

to the reliability of its weakest part. In a complex system human being-machine-work

environments, just the human being appears to be the weakest, the least known and controlled

element.

The development of science and technique changes the relation between physical and

mental work, the muscle work is reduced in favor of mental processes (perception, attention,

memory, thinking, decision). The responsibility of the employee is being increased, whereby

emotional stress due to anticipation of possible consequences of own failure is created, because

human error in operator’s activity can trigger serious consequences. The reliability of operator’s

performance, the capability to resist hindrances, safety of operator’s performance and/or the

possibility of his failure is an integral part of the reliability of the whole system and thus, also an

integral part of risk prevention. This is the reason, why it is necessary to minimize the percentage

of failures of the human factor, upon which the same requirements must be laid than on technical

facilities.

Mental workload of the employee

High requirements on labor, process tasks, conditions at which they are performed on the one

hand, and the properties, capabilities and possibilities of the employee on the other hand, can be

in a disharmony, and thus impose an undesirable mental workload on the individual. Usually, the

factors causing undesirable workload vary within a range of average values. In this case one can

speak about a light or medium workload. The psychical workload is high when the factors

causing it are so intensive that situations occur, which threaten the human being or cause

abnormal, erroneous, and thus unreliable responds. A hard psychical workload in the operation

process appears only seldom, however, one cannot exclude it. Here we must emphasize that also

permanent or long-term action of undesirable - though not hard – workload is reflected in the

operator’s performance and its health state.

Consequences of workload

1. In the sphere of living out a situation: all psychical states with different negative

emotional levels, e. g. fear, anxiety, threat;

2. In the sphere of motory manifestation: increased muscular tension, motory unrest,

mimics, secondary disorders of speech, disorders of motion stereotypes, etc.;

3. In the sphere of cognitive functions: on a lower level, the perception is being changed

(this situation is manifested by inattention, inaccuracy) and on higher level disorders in

ordering, thinking and reduced social adaptation;

4. In the sphere of physiological functions: changes of pulse frequency, blood pressure,

breathing frequency, etc.

From the above-motioned follows that consequences of undesirable workload can highly

negatively influence the human being activities, disintegrate the behavioral tendencies, negatively

affect safety and reliability of operator’s performance.

Consequences of a long-term excessive workload can be manifested at once: by employee ´s

failure in a certain situation, which need not be extraordinary. Then, incidents or accidents and/or

injury are related to the “human factor”, whereby rarely the real cause of human error is found.

More often, the consequences of excessive mental workload are manifested by bad mental state

of individuals, even by mental diseases. In the last years the health statistics have shown that

mental diseases (neuroses, depressions, anxiety, chronic fatigue, etc.) belong to the top ten

diseases, which are the reason of partial or total loss of jobs of human beings in their productive

age.

Also, psychosomatic gastrointestinal and cardiovascular diseases can be induced by a psychic

agent.

Primary workload

The primary workload is caused by own working activities. Many work places are highly

demanding and cannot be run without selection of employees by the assessment of their psychical

capability in relation to the demands upon work. We must take into account individual

characteristics of the employee, developing factors (most often connected with the age) and

transition variable factors. Judgment of the mental capability and identification of inner

determinants of erroneous, unreliable performance with regard to the demands given by operation

tasks requires the presence and intervention of a highly qualified specialist from the area of

psychological diagnosis.

Secondary workload

In contradiction with primary workload caused by own working activities, outer determinants of

performance reliability and/or behavioral errors result in secondary, additional workload. The

employees feel this kind of load as an attack on their psychical functions and processes, as

“straining” of their capabilities. These outer determinants represent direct hindrances in

perception and registration of information about the operation situation and consecutive solution

of the situation. Their negative influence on the employee is amplified by their “break through”

the employee. Thus, these determinants indirectly affect the individual ´s behavior, activities,

feeling , i.e. reliable performance as far as product quantity or quality and/or safety of operation

procedures is concerned. This second action of the above mentioned determinants causes

disorders of perception, disorders of attention and concentration, disorders of coordination of

motion, disorders of thinking and decision, disorders of the level of activity, disturbance of social

relations, whereby social relations act as one of the determinants of reliable or unreliable operator

´s performance.

Sources of secondary workload

Outer physical conditions

In the effort to eliminate negative and disturbing influences of the working conditions following

measures (found on the basis of safety analysis) should be taken:

devoted to the optimization of the work environments (improvement of local and global

lighting, decrease of noise, optimization of microclimatic conditions, color of the

workplace, better utilization of colors with regard to the labor safety, improvement of

orientation on the workplace, reducing of the toxicity in the atmosphere, etc.

technical character (additional improvement of machines, adding of supplementary

technical devices ensuring increased labor safety, optimization of the working tools,

improvement of the personal protective equipment, etc.)

production character (change of the technological procedures, involvement of

automatization, mechanization, change of operation procedures, etc.)

esthetic character (improvement of the work environments in terms of an esthetic

organization of the workplace

In addition to the improvement of operator’s performance and labor safety at the workplace,

optimization of the work environments yields also improvement of the feeling of comfort at the

workplace and of the mental and physical health of employees.

Organizing and controlling factors

Organization of labor, shifts, time schedules, responsibilities, authorities, information flow,

communication, systems of adaptation of new employees, education courses of employees –

these are all areas, in which secondary workload can occur.

Interpersonal relations

Unsuitable interpersonal relations cause that the attention is not drawn to tasks, which should be

fulfilled, but to other directions. The consequence is irritation, over-sensitiveness, feeling of

discomfort, stress, dissatisfaction and higher incidence of illness and injuries. The influence of

psychosomatic aspects on the reliability and safety of working performance is equally important

than the effect of action of physical factors, whether directly as an objective source of workload

or through a response in the psychical sphere as a subjective source of workload.

Depending on the quality of these factors of work environments, optimal or not optimal,

excessive workload will occur or the employee is able or not able to cope with this situation, or

avoid it. Thus, the individual can get in a vicious circle, in which the persisting objective sources

of workload with their negative consequences influence the working-performance preparation of

a human being and strengthen objective sources of workload.

Breakdown of equipment and not standard situations

In terms of operation safety it is important to train employees not only in the professional area,

i.e. to gain knowledge, skill and habits, but also to prepare individuals in the psychical area, i.e.

to maintain their adequate performance in nonstandard and stress situations. This should be an

integral part of accidents schedules and their training. The psychical training is devoted to the

diminishing and /or eliminating of anxieties or fears in case of not standard situations occurring

in running technological equipment. Unknown dangers are a greater psychical workload than

well-known dangers. If the employee gets successively familiar with the fact that the work

environment is a source of danger, but at the same time the individual does not know how to face

it, his/her consciousness is encumbered by factors, which are detriment in terms of mental

hygiene. Getting familiar with measures of protection against this danger, training and exercises

are not only a prevention of accidents and injury but also a mental hygienic action.

.

By neglecting prevention the requirements upon watchfulness of a person and his/her adaptability

to a risk situation increase. Safety labor requires human beings to adopt their activities to the risk

of a given situation. This adaptation, however, requires a good knowledge of specific danger on

the workplace. Labor performed at arbitrary danger always encumbers the human organism

psychically. To be conscious of danger does not always mean a perfect and watchful behavior,

but also fear, resignation and trust in fate. From this follows: each danger for an individual,

though being aware of it and trying to carefully face it, is safety defective in terms of labor.

Prevention, which removes outer danger, is at the same time a mental hygienic prevention.

Possible solutions of the problem – safety management system (SMS)

In solving problems of labor safety and health protection the human factor is an integral part of

the above-mentioned system human being – production unit – work environments. Thus, it is

necessary to take this factor into account also in case of prevention of injuries and diseases

caused by the job and incorporate it into the overall system of safety and health prevention

management.

The SMS management system is a system of principles and measures necessary for fulfilling

prescriptions of labor safety and health protection at workplace, principles of protection of

employees at workplace, permanent improvement of working conditions and working discipline

and the overall performance of employees. If we mention the overall performance, we mean also

the performance reliability of the employee in terms of quality, quantity or safety. Thus, we mean

the human factor in the production process. We should take into account the fact that labor safety

and health protection at workplace do not represent only traditional prevention against injury and

accidents but also all aspects of protection of employees connected with labor – for example

physical and psychical comfort, social protection, working conditions, working relations,

hygienic conditions, social conditions at work place, etc (I. Majer, 2002). In individual steps of

incorporating the SMS management system also the requirement of integrated incorporation of

the human factor must be taken into account.

HUMAN RELIABILITY ANALYSIS IN SLOVAKIA

Many of the hazard evaluation techniques can be used to identify the potential for human-

fai1ure-caused accidents. What-lf/Checklist analysis may consider issues concerning the potential

for an operator error. HAZOP study frequently inc1ude general operator errors as causes of

process deviations. It can be say that, these hazard evaluation techniques can be used to address

general human errors but on the other hand they tend to focus mainly on the hardware aspects of

potential accidents. When process operations inc1ude manual activities or when human machine

interface is very complex it makes difficult to use the standard hazard evaluation techniques to

evaluate the significance of potential human errors. Then it is clear that more specific method for

human factor evaluation, as Human Reliability analysis is needed. Human reliability analysis is a

systematic evaluation of the factors that influence the performance of operators, staff, technicians

and plant personnel. The primary purpose of human reliability analysis in the quantitative risk

analysis of chemical processes is to provide quantitative values of human error and to analyze the

characteristics of systems, procedures, and operators to identify likely sources of errors.

Quantitative assessment techniques of human error in chemical industries are used the same as in

nuclear power station in Slovakia – techniques THERP and TRC from SAIC

THERP

The Technique for Human Error Rate Prediction (THERP) (Swain and Guttman, 1983) is the

most widely used technique to date in nuclear power station in Slovakia. It is basically a hybrid

approach because it models human errors using probability trees and models of dependence, but

also it considers Performance Shaping Factors (PSFs) affecting the operator actions as:

Operating conditions.

Human abilities

Externally imposed factors

Time duration and fatigue

The technique is carried out in follow steps, each of which requires the performance of well

defined steps. These are namely :

Plant list

Review Information from fault tree analysis – check branches of fault trees for human

failures affecting the top event

Talk trough – familiarization with relevant procedures

Task analysis – break down tasks into smaller discrete units of activity such

Input information to human Evaluation processes Action to be taken Environments and constraints

Tools and job aids Manpower Communications

Develop HRA Event Trees – express each unit task sequentially as binary branches of an

event tree. Each branch represents correct or incorrect performance

Assign human error probabilities – data provided in the handbook (Swain and Guttman,

1983)

Estimate the relative effects of performance shaping factors - data provided in the

handbook (Swain and Guttman, 1983)

Assess dependece - equation for modifying probabilities on the basis of dependence

between tasks provided the handbook (Swain and Guttman, 1983)

Determine success and failure probabilities – total probabilities for success and failures by

multiplying branch probabilities and summing appropriately

Determine the effects of recovery factors – operators may recover from errors before they

have effect, recovery factors are applied to dominant error sequences

Perform a sensitivity analysis

Supply information to fault tree analysis – human error probability or rate

The implicit classification of human errors, included in the data base of THERP, contains errors

that are all reducible to two error types:

1. Error of Omission, by which a step or an entire task are omitted.

2. Error of Commission, which entails selection errors, such as issuing the wrong command

or selecting the wrong control, and sequence errors, such as time errors, i.e. too early or

too late execution, or qualitative errors, i.e. too little or too much.

THERP uses the Human Reliability Analysis Event Tree as its basic tool. By the use of this tree a

graphical description of the procedural step in a task is set out in a logical framework, which

implies that, at each node of the tree, there is a binary decision point, representing the failure or

the success of the current action. Hence these trees are compatible with conventional system

event trees, they can be evaluated in the formal mathematical sense, and consequently, once the

success or failure probability of each particular task steps in a procedure is known.

The key role of THERP is the determination of the probability that an error will result in a system

failure. This probability is assigned a value Fi. Branching trees are constructed to determine the

paths to system success and failure. The probability that an error will occur is given by Pi. FiPi is

the joint probability that an error will occur and that the error will lead to system failure. 1-FiPi is

the probability that an operation will be performed, which does not lead to system failure. The

probability that a class of errors will lead to system failure is given by:

(1)

where ni is the number of independent operations. The total system or subsystem failure rate is

given by:

(2)

where QT is the probability that one or more failure conditions will result from errors in at least

one of the n failure classes.

THERP allows the determination of the types, numbers, and skill levels of the personnel required

to operate the system. For system effectiveness, THERP allows an assessment of whether

uantitative requirements will be met. The determination of training requirements is more implicit

than explicit. Unacceptable task performance error rates suggest the need for training to improve

proficiency. Hence, THERP can suggest the need for training rather than specific training topics.

THERP can be applied to all types of equipments, tasks, and behaviors. With the aid of standard

human engineering techniques, it can be used for design analysis. Finally, THERP can be applied

to the early stages of system design as well as the later stages.

Table 1. Typical values of human error in nuclear power station in Slovakia evaluated by

THERP.

Code Description Probability value

OA(APR-PC) Operator doesn’t make fast decrease of pressure in PO - SGTR

5,0.10-2

OA(APR-SC) Operator doesn’t make fast decrease of pressure in SO 3,0.10-1

OA(AF) Operator doesn’t open 1 from 2 relief valve 3,0.10-1

OA(CS) Operator doesn’t start condense pumps 5,0.10-2

OA(DM) Operator doesn’t start pumps for demi-water 0,4 MPa 5,0.10-3

OA(DRAIN) Operator doesn’t fill out channels to HZ 1,0.10+0

OA(DW) Operator doesn’t start pumps for demi-water 1 MPa 5,0.10-3

OA(EF) Operator doesn’t open valves in system SHNČ 5,0.10-3

OA(FWH-I) Operator doesn’t split HNK 1,0.10-2

OA(FWL-I) Operator doesn’t isolate feed pipe 1,0.10-2

OA(IFSL-I) Operator doesn’t isolate interfacing LOCA 2,0.10-3

OA(IM) Operator doesn’t open valves 5,0.10-3

OA(LP-OVERFL) Operator overflow storage tank TH 4,0.10-2

OA(MC-LOOP) Operator error to stop release from the loop 5,0.10-3

OA(RH) Operator doesn’t start RH system 1,0.10-3

OA(RH-ATM) Operator doesn’t open cooling system PSA 5,0.10-3

OA(SGTR-I) Operator doesn’t isolate loop SGTR 5,0.10-2

OA(SH-I) Operator doesn’t isolate HPK 5,0.10-3

OA(SL-I) Operator doesn’t isolate small release 5,0.10-3

OA(TB) Operator doesn’t start TB system 5,0.10-3

OA(TK50) Operator doesn’t open valve in the node TK50 5,0.10-3

OA(VSL-I) Operator doesn’t isolate very small release 5,0.10-3

OA(WM) Operator doesn’t start TK pump 5,0.10-3

OPER.PRE ACC Human error before accident 3,0.10-3

TRC

Dougherty and Fragola (1988) have introduced the time-reliability correlation (TRC) system.

Basic input parameter for TRC method is time, which is available for the action related with

human error. This approach uses simulator training results to create a family of time-reliability

correlations, which are adjusted with either the Success Likelihood Index (SLI) or other expert

judgment methods to account for special conditions. TRC is the relationship between human

performance reliability and time. Data from simulators suggest that the lognormal distribution is

sufficient for modeling. The SLI is derived in the following manner:

(1) To choose the influences appropriate to the event and the situation.

(2) Rank the influences as multiples of the least important for a given situation, which is set

at "10."

(3) Sum the rankings of all influences and normalize the rankings to this sum.

(4) Assess the impact of each influence from best (1) to worst (10).

(5) Compute the "dot product" of the ranking and the quality vectors. This is the SLI.

(6) Apply the SLI. Mathematically, the SLI is expressed by:

(3)

and ri is the rank of the influence i and qi is the quality of the influence i. Dougherty and Fragola,

1998 focus on a lognormal TRC based on simulator data. This is in consonance with the modified

Human Cognitive Reliability (HCR), which was developed by Hannaman et al. 1984 for

calculating the operator probability of non-response to a cognitive processing task as a function

of time. The type of cognitive processing may be rule based, skill based, or knowledge based. For

task j, the probability of non-response P(t) is given by:

where Tmed is median time to perform the task corrected by a shaping factor Kj, bj is shape

parameter, Cgj is time delay factor as a fraction of Tmed for type j cognitive processing Cnj is scale

parameter as a fraction of Tmed for type j cognitive processing.

Furthermore the probability of human error which are generated by TRC methods can be

modified by the follows criteria: training situations, non-training situations (so called recovery)

and mental endurance.

In the case of training situations the operator follows special and transient procedures and

also other relevant procedures for action performance. Non-training situations are characteristic

with non-availability of accurate and complete procedures or missing other relevant procedures

like specific criteria of operator intervention for action performance. Mental endurance has

negative influence at human performance mainly under stress and it should be combined with

non-training situations if do not exist any training situations. The probability of human errors

generated by TRC methods in nuclear power station in Slovakia is reviewed in tables 2-5.

Table 2 Probability of human error for training situations without operator uncertainty.

Time minSuccess Likelihood Index (SLI)

0,1 0,3 0,5 0,7 0,95 3E-1 2E-1 1E-1 6E-2 3E-210 9E-2 4E-2 2E-2 8E-3 3E-320 1E-2 5E-3 2E-3 5E-4 1E-430 3E-3 9E-4 3E-4 6E-5 1E-560 1E-4 3E-5 6E-6 1E-6 2E-7

Table 3 Probability of human error for training situations with operator uncertainty .

Time minSuccess Likelihood Index (SLI)

0,1 0,3 0,5 0,7 0,95 4E-1 3E-1 2E-1 2E-1 1E-110 2E-1 1E-1 9E-2 5E-2 3E-220 7E-2 4E-2 3E-2 1E-2 8E-330 3E-2 2E-2 1E-2 6E-3 3E-360 8E-3 4E-3 2E-3 9E-4 4E-4

Table 4 Probability of human error for non-training situations without operator uncertainty Success Likelihood Index (SLI)

Time min 0,1 0,3 0,5 0,7 0,95 7E-1 5E-1 4E-1 3E-1 1E-110 3E-1 2E-1 1E-1 6E-2 3E-220 9E-2 4E-2 2E-2 8E-3 3E-330 3E-2 1E-2 5E-3 2E-3 5E-460 3E-3 9E-4 3E-4 6E-5 1E-5

Table 5 Probability of human error for non-training situations with operator uncertainty.

Time minSuccess Likelihood Index (SLI)

0,1 0,3 0,5 0,7 0,95 6E-1 5E-1 4E-1 3E-1 3E-110 4E-1 3E-1 2E-1 2E-1 1E-120 2E-1 1E-1 9E-2 5E-2 3E-230 1E-1 7E-2 4E-2 3E-2 1E-260 3E-2 2E-2 1E-2 6E-3 3E-3

The quantification of human error poses problems for a number of reasons:

Incident records rarely describe the environmental conditions (or performance shaping

factors) under which the human errors were made. This makes it difficult to generalize

from failure data for specific tasks to others that are similar.

Incident records often-record only errors, which have resulted in some modifiable

consequence. They do not record either opportunities for error or error frequencies with

no consequence (e.g. because of error recovery). It is not possible to determine, therefore,

what the true error rate is.

Some of the techniques for quantification of human reliability require the use of

subjective judgment by experts. Bias in making expert judgments and in judging error

probabilities for new designs of systems which have not yet been operated exacerbate the

problem, although progress has been made in 'structuring' the judgments in order to

reduce the bias.

Without quantification of human factors, quantitative risk assessment reduces to an analysis of

hardware, predicated on an implicit assumption that all the human factors involved are about the

same as the industry average. This is usually a sensible assumption, because the quantitative risk

assessment is supposed to valid for the plant lifetime and operator performance will vary during

that time. However, it should be note that such an assumption is being made.

.

Overview of information provide on human factors to Seveso II safety reports in Slovakia.

Identification of working positions, which can have influence at safety of system or subsystem;

Description and short characterization of working positions;

Analysis and human reliability assessment of certain working positions:

To indicate critical places in human – machine interaction

To summarize the set of human errors and they potential causes (HAZOP and the other

qualitative hazard techniques;

To provide quantification of human reliability assessment (quantitative technique is not

direct recommended);

Categorization/descriptions difficulties of subsystems (compound hardware, complex of start-up

or shut-down procedures and difficulties with communications);

To declare the system of people selection at working positions:

Physical health and to indicate the periodical monitoring;

Personal factors (mental health, self-control, resistance at stress)

To declare regular performance of next activities:

Ergonomics default

Default and uncertainty with software

Uncertainty and exact define responsibilities for operators

Undesirable workload

Undesirable rotation of working period

Non-favorable working conditions

Outside working influence – live style

To provide information about the risk which follows from their working activities

Training of hazard situation and emergency response

Level of communication in regular and critical situations

To collect information about needs, feelings and comments of workers/operators.

Future development in Slovakia

It is clear that human reliability analysis techniques have been developed and applied in the

nuclear industry and there is an evident need to adapt these techniques to the chemical industry.

On the other hand, this it is not an easy goal because this requires the generation of human

reliability data appropriate to the chemical industry. Currently a few data exist but these data may

be inappropriate due to differences in environment, training, stress levels and etc. Direction of

improvement in the use of human factors methods in quantitative risk assessment in chemical

processes in Slovakia can be in:

Continued improvements in models for incorporating human factors into a quantitative

risk assessment in chemical processes.

Human factors analysis focus on the dynamical aspect of human – machine interaction

because, by the dynamical analysis, it becomes possible to consider specific sequences and

accident paths, which are not identified by the traditional way.

Better understanding of the impact of company and plant culture, management systems,

maintenance practices on the reliability of process plant equipment, in the case of modern plants,

the root causes of human errors can be effectively identified by the application of an accurate and

structured method that accounts for the cognitive processes in the management system.

To developed generally available data for human error.

Finally it can be said that human error is commonly found to be the dominant factor in

determining the frequencies of major incidents, thus uncertainty in estimating human error rates

may be the dominant factor in the uncertainty of the event frequency. On the other hand, it has to

be noted that the deep information can be also obtained by non-numerical descriptive type of

analysis, which is important for the evaluation of findings from the accident investigation and for

the assessment of the working and control procedures.

References

Štikar, J.: - Hoskovec, J. - Stríženec, M.: Inženýrská psychologie, SPN, Praha 1982

Majer, I.: Príručka na zavedenie jednoduchého systému riadenia bezpečnosti a ochrany zdravia pri práci v malých podnikoch, Pravidlá dobrej praxe BOZP 1, NIP, Bratislava 2002

Swain, A. D., and H. E., Guttmann Handbook on Human Reliability Analysis with Emphasis on Nuclear Power Plant Application. NUREG/CR-1278. SAND 80-0200 RX, AN. Final Report, (1983),

Dougherty, E.M. and J.R. Fragola, Human Reliability Analysis, Wiley, (1988)

Hannaman, G.W., A.J. Spurgin, and Y.D. Lukic, "Human Cognitive Reliability for PRAAnalysis," NUS-4531, NUS Corp., 1984.