AFFIDABILITA' E SICUREZZA DEI SISTEMI PRODUTTIVI

Knowledge and understanding

The course develops students' awareness of risk and safety management in complex systems. On completion of the course, students command the technical vocabulary and the core concepts of risk analysis and assessment; they know the deterministic and stochastic models of reliability theory for the assessment of components and systems, including repairable ones, and the qualitative and quantitative methodologies for hazard identification and risk analysis; they know the technical and organisational aspects of safety, reliability and maintenance management, aimed at the design and management of the safety of people, assets and the environment; and they understand the essential elements of both binding legislation and voluntary standards concerning occupational safety and the safety of industrial plants.

Applying knowledge and understanding

On completion of the course students are able to:

●        perform reliability calculations for components and systems in standard configurations (series, active parallel and stand-by) and in complex configurations, including through the identification of minimal cut sets and tie sets;

●        set up and solve the Markov model of a repairable/non-repairable system, deriving the transient and steady-state reliability parameters, also by means of Laplace transforms;

●        build and quantify a fault tree and an event tree starting from the functional description of a plant and from the available failure data;

●        carry out a HAZOP study on one or more nodes of a process plant, applying the guide words, identifying causes, consequences and existing safeguards, and formulating recommendations for safety improvement;

●        set up the risk analysis of a job task, identifying the hazards, estimating the risk and selecting collective and individual prevention and protection measures consistent with the general protection measures laid down by binding legislation or by good technical practice;

●        select and justify the most appropriate maintenance policy and strategy for a component or a system, according to its failure behaviour and to the consequences of failure.

Making judgements

Students develop the ability to choose among qualitative, semi-quantitative and quantitative analysis methods and to justify their adequacy to the problem at hand, to judge the representativeness and the limitations of the failure data used, and to express a reasoned opinion on the acceptability of residual risk. These abilities are developed through guided exercises and through the HAZOP analysis or the job-task risk analysis project, which require assumptions to be made under incomplete information and to be defended.

Communication skills

Students acquire the ability to document reliability or risk analysis using appropriate technical terminology and in the formats used in professional practice (HAZOP worksheet, analysis report, risk assessment document), and to present its results to specialist and non-specialist audiences. These skills are developed through the drafting of the project reports and their presentation and discussion, normally in groups, at the examination.

Learning skills

Students acquire the ability to independently retrieve, read and interpret primary legislative sources and technical standards, and to update their knowledge within an evolving regulatory framework. These skills are developed through guided individual study of the legislation and technical standards referred to in class, and through group project work, which requires the autonomous search for data and references.

The course, worth 9 ECTS credits, comprises 93 hours of teaching activity, divided into 28 hours of lectures and 65 hours of tutorials, plus 132 hours of individual study, for a total workload of 225 hours.

Lecture-based teaching — 28 hours. Lectures devoted to the presentation of theoretical contents: probabilistic foundations, reliability theory, Markov models, maintenance concepts, risk analysis methodologies and the regulatory framework. Lectures are supported by slides and lecture notes made available on the Studium platform before each topic is addressed.

Interactive teaching — 65 hours. Qualitative and quantitative (numerical) exercises carried out in class with the active participation of students in problem solving; analysis and discussion of application cases, accident case studies and plant documentation; group development of the HAZOP analysis on real plant documentation provided by the lecturers, with intermediate reviews where applicable; alternatively, development of the job-task risk analysis project; mid-term test and assessment of the topics covered.

 

Consistency between teaching methods and expected learning outcomes

●        Lecture-based teaching supports the «knowledge and understanding» descriptor, presenting reliability models and the body of legislation in systematic form.

●        Qualitative and quantitative exercises and the mid-term test support the analytical component of the «applying knowledge and understanding» descriptor, since they require the independent use of models on problems of increasing complexity.

●        The HAZOP analysis and the risk analysis project support the «making judgements» and «communication skills» descriptors, since they require assumptions to be made and defended under incomplete information and results to be documented in professional formats.

●        Guided study of legislative sources and technical standards supports the «learning skills» descriptor, in a field where the regulatory framework is subject to frequent change.

 

If the course is delivered in blended or remote mode, appropriate adjustments may be made to the above, to ensure consistency with the syllabus.

Curricular prerequisites: none.

Cultural prerequisites. To follow the course profitably, the following prior knowledge is required:

●        essential: elements of mathematical analysis (function study, differentiation and integration, first-order linear ordinary differential equations) and notions of Boolean algebra;

●        important: combinatorics, probability theory (conditional probability, Bayes' theorem) and the main discrete and continuous probability distributions; Laplace transforms;

●        useful: basic notions of production systems and industrial plants, ability to read a process diagram and a functional block diagram; technical English reading comprehension at CEFR level B2.

The knowledge listed as «important» is briefly revised at the beginning of the course; this does not replace individual study.

Attendance is compulsory. Under the Teaching Regulations of the Master's Degree Programme in Management Engineering, students are required to attend at least 70% of the course teaching hours.

Beyond the formal requirement, active participation in teaching activities is decisive for achieving the expected learning outcomes: exercises and the development of the risk analysis are interactive teaching activities carried out in class and cannot be entirely replaced by individual study, since much of the learning arises from discussing the assumptions made and from the progressive review of the reports. In particular, the HAZOP analysis is carried out in groups, with intermediate reviews with the lecturers where applicable.

Students who are unable to attend are invited to contact the lecturers at the beginning of the course in order to agree on arrangements for the project activities compatible with their situation. Complete teaching material is in any case available on the Studium platform.

1. Introduction and definitions. The concept of safety. Hazard, risk, exposure and harm. Risk assessment and safety analysis. Residual risk and acceptability criteria.

2. Combinatorics revision (prerequisite alignment, not an examination topic). Factorials, Newton's binomial, arrangements, permutations and combinations. Cartesian product of sets. Tree diagrams.

3. Probability theory revision (prerequisite alignment, not an examination topic). Definition of probability and properties of probability calculus. Discrete random variables. Conditional probability with examples. Multiplication rule and Bayes' theorem.

4. Statistics revision (prerequisite alignment, not an examination topic). Discrete and continuous probability distributions of interest in reliability analysis.

5. Classical reliability theory. Reliability and unreliability functions. Failure rates and MTTF. Simple reliability configurations: series and active parallel. Derivation of reliability functions for active parallel, cold stand-by and warm stand-by. Complex systems: cut sets and tie sets. Exercises.

6. Application of Markov theory to system reliability. Stochastic processes. Markov processes and Markov chains. Laplace transforms revision. Repairable safety systems. Application to systems in the most common reliability configurations (series, active parallel, including k-out-of-n logic, cold stand-by, warm stand-by, complex configurations). Exercises.

7. Introduction to maintenance concepts. Maintainability and availability. Maintenance policies and strategies. Reference terminology (UNI EN 13306).

8. Risk analysis. Risk analysis methodologies: historical analysis, checklists, HAZOP (IEC 61882) and FMEA/FMECA (IEC 60812). Fault Tree Analysis: Traditional FTA (IEC 61025) and Dynamic FTA (DFT). Event Tree Analysis: ETA (IEC 62502). Index methods.

9. Major-accident hazard legislation. Directive 2012/18/EU (Seveso III) and its transposition by Legislative Decree 105/2015: scope and dangerous substances, lower-tier and upper-tier establishments, safety report, internal and external emergency plans.

10. Machinery safety legislation. Regulation (EU) 2023/1230: essential health and safety requirements (Annex III), conformity assessment and CE marking, technical file, safety software and substantial modifications. Duties of the employer as user of work equipment (Legislative Decree 81/2008).

11. Occupational health and safety legislation. Legislative Decree 81/2008 as amended: general protection measures, delegable and non-delegable duties of the employer, risk assessment and contents of the risk assessment document (Art. 28(2)), assessment procedures, prevention and protection service, information, training and instruction, other roles relevant to workers' safety and their duties.

12. Workplace safety: specific risks. Personal protective equipment (Regulation EU 2016/425). Fire risk and fire safety measures. Ergonomics of display screen workstations. Chemical risk and dangerous substances (safety data sheets). Manual handling of loads. Mechanical risk and protection against moving parts.

13. Numerical exercises. Exercises on classical reliability theory, on Markov theory applied to reliability, and on the construction and quantification of fault trees.

14. HAZOP analysis (group work). Analysis of one or more nodes of an industrial plant using the HAZOP methodology, carried out in groups on plant documentation provided by the lecturers.

15. Job-task risk analysis project (activity replacing the HAZOP analysis). Risk analysis of a job task agreed with the lecturers.

Reference texts

D1. Lecture notes and slides, available on the Studium platform (https://studium.unict.it) to all enrolled students.

E1. Modarres M., Groth K., Reliability and Risk Analysis, 2ª ed., CRC Press, 2023, ISBN 9781032309729 (hbk 9781032309736; ebk 9781003307495).

E2. Rausand M., Haugen S., Risk Assessment: Theory, Methods, and Applications, 2ª ed., Wiley, 2020, ISBN 9781119377238.

Recommended further reading

E3. Rausand M., Barros A., Høyland A., System Reliability Theory: Models, Statistical Methods, and Applications, 3rd ed., Wiley, 2021, ISBN 9781119373520.

E4. Zio E., An Introduction to the Basics of Reliability and Risk Analysis, World Scientific, 2007, ISBN 9789812706393.

Legislative sources

N1. Legislative Decree 81/2008 as amended, consolidated text available on the Normattiva database (https://www.normattiva.it).

N2. Legislative Decree 105/2015 (transposing Directive 2012/18/EU).

N3. Regulation (EU) 2023/1230 and Legislative Decree 17/2010, available on EUR-Lex (https://eur-lex.europa.eu) and on Normattiva.

Structure of the assessment

Learning is assessed through two written tests, one numerical and one theoretical, normally held on the same date unless the mid-term test has been passed, and through the oral discussion of the risk analysis (HAZOP or job-task risk analysis), normally held on a separate date.

Mid-term test. A mid-term test of approximately 75 minutes is held during the course, covering the numerical exercises part (reliability, Markov models, fault trees). The test is passed with a mark of at least 18/30; the mark obtained contributes to the proposed final mark and replaces the corresponding part of the final numerical written test. Its validity is limited to the examination sessions of the current academic year.

Final written test. In the examination sessions following the course, the written test lasts approximately two hours and thirty minutes and consists of two parts. The theoretical part comprises approximately one hour for five open-ended questions on the syllabus topics and one theoretical exercise involving proofs relating to reliability, with no reference material allowed, plus 15 minutes for a multiple-choice test of 15 questions, with reference material allowed. The numerical exercises part lasts approximately 75 minutes and comprises two applied exercises; it is not required of students who have passed the mid-term test. During the numerical test, calculators and Laplace transform tables may be used. A mark of at least 18/30 is required to pass the written test, which is a condition for admission to the oral discussion.

Oral discussion of the risk analysis. Normally on a date other than the written test, group and/or individual works (HAZOP analysis or job-task risk analysis project) are presented and discussed, for approximately 45 minutes per group. Each group member answers on the whole report. Students who pass the written test and present their report are offered a mark and the passing of the course.

 

Assessment criteria

The theoretical written test assesses the relevance of the answer to the question asked, the correctness and completeness of contents, the ability to summarise, the correctness of the formulation and analytical development of the theoretical exercise, and command of technical language.

The numerical written test assesses the methodological approach, the correctness and completeness of intermediate and final calculations, the orderliness and systematic nature of the development, and the consistency of any assumptions made and of the results obtained.

The risk analysis discussion assesses the methodological correctness of the analysis, the justification of the assumptions, the accuracy of the report and of the proposed recommendations, and clarity of presentation.

The final mark, expressed out of thirty, is determined as follows: theoretical written test (40%), numerical written test or mid-term test (40%), risk analysis discussion (20%). Within the theoretical written test, the weights are: open-ended questions (55%), theoretical exercise (30%), multiple-choice test (15%).

The final mark is awarded according to the following parameters:

●        fail: students do not possess the minimum required knowledge of the main course contents; their ability to use specific language is poor or absent and they are unable to apply the acquired knowledge independently;

●        18-21: students have minimal knowledge of reliability and risk analysis methods and of the regulatory framework, show limited ability to critically analyse the cases presented and expound sufficiently clearly, although their command of language is poorly developed;

●        22-25: students have fair knowledge of the contents, although limited to the main topics; they are able to integrate and critically analyse the cases presented, though not always coherently, and expound with fair command of language;

●        26-28: students have good knowledge of the contents, analyse the cases presented critically and coherently, solve complex reliability problems fairly independently and expound using appropriate language;

●        29-30 with honours: students have thorough knowledge of the contents, integrate and critically analyse the cases presented, independently solving even highly complex problems, and demonstrate excellent communication skills and command of language.

 

Examination booking

Booking for an examination session is compulsory and must be made exclusively online through the Student Portal, no later than three working days before the examination date. Examination dates are published on the Degree Programme website.

 

Learning assessment may also be carried out on-line, should the conditions require it.

To ensure equal opportunities and in compliance with current laws, interested students may request a personal interview in order to plan any compensatory and/or dispensatory measures based on educational objectives and specific needs. Students can also contact the CInAP (Centro per l'integrazione Attiva e Partecipata — Servizi per le Disabilità e/o i DSA) referring tutor within their department (https://www.cinap.unict.it/content/referenti).

THEORETICAL WRITTEN TEST

Open-ended questions

●        Explain the difference between active parallel, cold stand-by and warm stand-by.

●        Write the analytical definitions of the reliability function, the unreliability function, the failure probability density function and the failure rate in the case of random failures, and draw the corresponding diagrams.

●        Briefly describe the advantages, the disadvantages and the field of application of the risk analysis methodology known as Checklist.

●        State the criteria for the use of self-contained (isolating) respiratory protective devices.

●        Describe the main risk factors associated with the use of display screen equipment, briefly outlining their causes.

 

Theoretical exercise

●        Derive the reliability function of a 1-out-of-2 cold stand-by system with an ideal switch, using classical reliability theory.

●        With reference to repairable safety systems, draw the diagram showing the potential states of the system over time, where failure is revealed only at the periodic proof test and maintenance (of duration r) is carried out irrespective of the occurrence of a failure. Then draw the corresponding Markov diagram, highlighting the states that contribute to the PFD.

 

Multiple-choice test

●        In order to reduce the frequency of occurrence of an accidental event, the required measure is: [a] prevention — [b] protection — [c] both.

●        In the signage for dangerous substances, the pictogram showing a skull and crossbones indicates a substance that is: [a] toxic — [b] harmful — [c] irritant.

 

NUMERICAL WRITTEN TEST

·       Given the plant diagram (P&ID section) shown in the figure, whose operating principle is known:

R1. Draw the fault tree for the Top Event = «XXX».

R2. Determine the minimal cut sets, indicating at each step the properties of Boolean algebra used.

R3. Compute the probability of the Top Event. For events with given MTTF and MTTR, assume constant rates and repairable components; rare-event approximations are allowed, provided they are justified.

R4. Propose a design modification that improves reliability, explaining how the structure of the tree changes and computing the new probability of occurrence of the Top Event.

·       Given the reliability block diagram (RBD) shown in the figure:

Q1. Draw the state diagram according to Markov theory, indicating the corresponding transition rate for each arc.

Q2. Write the transition rate matrix A and the system of differential equations.

Q3. Assuming the failure rates given in the table, solve at least three equations of the system, choosing them among those of the states with at most one failed component, for a mission time t = 1000 h.