The HAZOP (HAZard and OPerability) technique is a scenario-based risk assessment procedure. It is typically used to determine what hazards may occur and what safety barriers (Protection Layers) should be adopted.
The HAZOP technique and its many variants, defined by the IEC 61882 standard, originated from insurance type studies on large process plants, extending the application to detailed analysis of a wide range of risks during the design and operation phases of a given process. The technique was developed to identify and assess risks in a plant and to identify problems with normal operations and safety procedures. Due to the detailed information required it can only be implemented while or at the end of the executive design. The limits of the plant under examination must be defined in detail with the aid of the documents used in successive phases for the execution of the study: plans, running diagrams, functional diagrams, flow diagrams, equipment specifications, single-line electrical diagrams, suppliers' detailed drawings, operating manuals, emergency procedures. The use of incomplete or outdated documents can significantly compromise the quality and results of the study, so it is essential to work on "as built" documentation, i. e., final construction and updated version.
Risk and operational analyses are developed to allow a formal, systematic and critic examination of the design and procedural intentions of a system. These analyses shall enable the identification and assessment of possible risks and malfunctions of individual parts of the installation and the consequences for the system. The formal structure of this technique ensures that all risks related to the activity under analysis are identified, through brainstorming and direct comparison between the experiences of different people and company functions. The main disadvantage is related to the long lead times and therefore the high costs.
The HAZOP operation modalities require the assistance of experts and operators involved in a multidisciplinary team that works according to the objectives and the program of the study established by the client. The team must use a systematic and creative approach to analyze the plant and logically correlate individual accidental occurrences, identifying interactions of occurrences that could lead to unwanted consequences.
Systematicity can be achieved in several ways. For example, the "guiding words" method involves a combination of "guiding words" and "process variables", through which is determined a dynamic characterized by alternating questions and answers between leaders and team members. The leader defines, in each P&ID (Process and Instrumentation Diagram), a series of unique points and sections bounded by multiple nodes. All that provide an excellent basis for drawing up operating manuals for individual parts of the plant and for evaluating written procedures.
Team meetings are useful to identify the hazards that exist in the management of a work process. These hazards are identified and investigated based on deviations, whether accidental or not, of key parameters, characteristic of the process under examination. This analysis is carried out through a phase of defining the working environments and understanding the work processes that take place in them, in a subsequent examination of parameters (with deviations and their consequences), to proceed finally to the recording of conclusions on possible hazards and useful recommendations for their management. It is critical to derive a table of logical correlations between events, team findings (risks, operational issues), recommendations for changes and insights related to the process, facility and procedures.
Tab.1 Hazop table example (ResearchGate)
While the HAZOP method is used to identify potential risks associated with the operation of an installation or activity, the HAZard IDentification (HAZID) method works similarly by identifying the risk in relation to an EUC (Equipment Under Control) system and associated control. Everything is done in accordance with ISO 17776 (Guidelines for Instruments and Techniques for the Identification and Assessment of Hazardous Events) and ISO 12100 (Safety of Machinery – General Principles of Design – Risk Assessment and Risk Reduction).
The objective of the HAZID phase is therefore to identify the potential hazard inherent the controlled system, without recurring to the implementation of safety-related functions. The obtained result must be sufficiently detailed to allow identification of potential deviations from the minimum SIL (Safety Integrity Level) requirements.