Hazop – Wikipedia

The methodology of dangerous analysis and operability (O Hazop , from English HAZard and OPerability analysis ^[first] ), aims to examine the work environments and identify the dangers to which these environments expose workers.

The Hazop technique originated from insurance studies, especially on large process plants, extending its application to different areas and sizes. Operating methods require the competition of experts and operators involved in a team multidisciplinary who works by reaching the purposes and programming of the study established by the client.

The main characteristics of the techniques used in the analysis/risk assessment are:

• Checklist: one of the simplest methods; It consists of a predefined series of questions or topics to be examined. It is the “Knowledge Based Hazop”, developed by the Exxon.
• What-IF Analysis: it is conducted using a brainstorming approach; it starts with analyzing dangers already known to the team of work, to get to other potential incidental scenarios. Mentioned in the OSHA standard 1910.119 and in the CEI UNI EN IEC 31010 standard Risk management – risk assessment techniques . ^[2]
• Analysis of the ways and effects of faults (or FMEA, from English Failure mode and effects analysis ): evaluation of the possible failure ways of the individual components of a system and the consequences that these failures cause on the system.
• Hazop: group exercise, which takes place through the formulation of some specific structured questions; It is aimed at identifying deviations from the project intent that can lead to security or exercise inconveniences.

Hazop is one of the best known and widely adopted techniques, also by International Normation Bodies :

• European Process Safety Center, HAZOP,Guide to Best Practice (2008)
• European Process Safety Center, Hazard Identification Methods (2003)
• Kletz T. “Hazop & Hazan” (4th EDN), Icheme (2006)
• CCPS “Guidelines on Hazard Evaluation Procedures, 2nd Edn”
• IEC 61882 Ed. 1.0 b:2001: Hazard and operability studies (HAZOP studies) – Application guide
• OSHA 1910.119 : Standard for the management of process safety of plants in which very dangerous substances are used. He cites the Hazop among the recommended techniques for identifying the dangers.
• DEF STAN 58 : standard published by the British Ministry of Defense. It provides precise indications on the use of Hazop in the study of programmable electronic systems (PES).
• Chemical Industries Association (1990): body to whom companies in the chemical sector adhere; He has published guidelines to follow in Hazop studies applied to the process industry.
• American Institute for Chemical Engineers (1985): has published a volume dedicated to the Hazop technique, inserted in a monographic necklace edited by Centre for Chemical Process Safety .

In Italian legislation, even in the absence of mandatory references to this technique, there are notes, especially for the parties concerning complex plants ( Relevant risks, according to what is defined by the European directive 82/501/EC and subsequent amendments ).

Approach [ change | Modifica Wikitesto ]

Hazop is based on a group work, carried out in sessions, aimed at identifying the existing dangers in the management of a specific work process. These dangers are identified and investigated on the basis of deviations, whether they are accidental or not, of key parameters, characteristic of the process in question.
This analysis is conducted through a phase of defining the working environments and the understanding of the work processes that take place, in a subsequent examination of parameters, their deviations and related consequences, to proceed with the registration of conclusions on possible dangers and useful recommendations for their management.
Characteristic of the Hazop are the way of the working group and the methods of defining the content of the study.

• The Hazop team: the leader are part (ask questions to the team and coordinates the works), the secretary (takes note of the key points of the discussion) and representatives of each of the main disciplines for the system studied, which are:
  • process
  • exercise
  • Safety and maintenance.

• The system in question: it is defined at the beginning of the Hazop, normally using plans, functional patterns, driving patterns, uniform electric patterns of the system and clearly identifying battery limits and interfaces with other systems.
• The team at work: through the use of guidance words (” The basis of HAZOP is a guide word examination ” – IEC 61882 2001), questions are asked and refined answers regarding deviations from the project intent of the process variables or the system failure ways.

Dynamics [ change | Modifica Wikitesto ]

The dynamic of the Hazop is characterized by an alternation of questions and answers between leaders and team members.
The leader defines, in each P&D, a series of singular points (nodes) and sections delimited by multiple knots; For each section, the team examines the possible deviations of the variables from the project intent.
The leader formulates a series of questions; Through a group discussion, the members of the Hazop team try to reach a shared response:

• The questions asked by the leader are based on the systematic use of guidance words
• The questions aim to solicit the group discussion on the ways in which the functioning of the system or a part of it could differ from the intent of the designers
• For each deviation, the team wonders about the possibility that a dangerous condition arises
• The secretary records the salient points of the discussion for each guide.

Field of application [ change | Modifica Wikitesto ]

The limits of the plant in question must be defined in detail before the start of the Hazop, with the help of the documents that will subsequently be employed for the execution of the study. In particular:

• Planting drawings and patterns, such as plans, driving patterns, functional diagrams, are normally used to circumscribe the study area.
• Further useful consultation documents:
  • flowcharts
  • specifications specifications, supplier detail drawings.
  • operating manual and emergency procedures.

The use of incomplete or non -updated documents can significantly compromise the quality and results of the study, therefore it is essential to work on “as built” documentation, that is, in a final construction version and updated to take into account any changes that occurred. In addition to the process industry, the Hazop technique is effectively applied usefully to various types of systems, as indicated in the table:

Study topic	Reference diagram	Type of parameter
Electricity distribution	Uniform diagrams	Electric
Critical safety software	Information flow diagram	Data
Electro-pneumatic components	Electric and tire circuits	Electromechanical
Operative manual	Analysis “Herchy homework”	Human action

For the success of the Hazop it is essential that the available documentation provides an exhaustive description of the way in which the system is called to work.

Equally important is the availability of reliable information on the operating conditions for interfaces with other systems. Not infrequently, in fact, dysomogeneities existing on the border points are at the origin of dangerous situations.

Planning [ change | Modifica Wikitesto ]

The key documents should be made available at least a week before the start of the Hazop, in order to allow adequate planning of the study.
It is important that the Hazop leader obtains documents with a reasonable advance, so that it can become familiar with the system and the methods of representing the process.

Before the start of the study, the leader meets the members of the team and informs them about how the study and the guidance words that will be used will be conducted.
The proposed program must be compatible with the chosen office for the conduct of the study and the needs of the members of the working group, taking into account the need, by the team, to be able to work undisturbed in two daily sessions, each lasting about 3 hours, verifying the actual availability of all interested parties.

The duration of the study also depends on the methods of recording the discussion: a complete register requires that every guide used to be noted, while it is faster to consider only those deviations that can give rise to a dangerous condition

Pauses in number and duration must be provided to keep the level of attention and concentration of the participants high. In particular, prolonging the duration of the work sessions over six hours a day is often counterproductive: the concentration of the working group inevitably drops and the quality of the work is affected.

At the end of each day of work, moreover, leader and secretary must dedicate time to the revision and completion of the notes and prepare copies to be distributed to each member of the team the next day.

The experience acquired in previous studies allows you to estimate the duration of a Hazop on the basis of the average daily number of P&D which can be examined.

The choice of the meeting room and its location is also important.

The meeting room must be spacious, the work table must be sufficient to allow each participant to be able to follow the study, keeping in front of it a copy of the documentation under discussion and other work documents.

The secretary must have sufficient space for the arrangement of a laptop, used for the transcription of the notes. It is good practices to fix the general plans and the flow schemes of the processes under investigation to the walls of the room, to make the understanding of the process and control of interfaces between plants or plant sections more immediate.

The working group [ change | Modifica Wikitesto ]

The choice of members of the working group must fall on the company’s staff in possession of the necessary technical and operational skills, which must be freed from other work commitments for the entire duration of the study.

Specific positions are assigned to each member of the working group:

• The leader has the role of chairman . It is he who formulated the questions and to stimulate the discussion and participation of the other team members on the topics from time to time.
• The secretary takes note of the key points of the discussion, organizes the work sessions and prepares the preliminary versions of the Hazop document, to be circulated daily among all the participants.
• The members of the group represent the main technical disciplines involved.

Other specialists can be called to participate for limited periods, where necessary.

The numerical composition of the group can vary between 4 and 12 elements: groups too numerous slow down the pace of work and limit the discussion, while in too small groups the global vision of the problems treated is lacking.

The leader [ change | Modifica Wikitesto ]

The main role of the leader is to encourage discussion and comparison. This objective is pursued by the President:

• keeping the Hazop group concentrated:
  • reiterating that it is a question of identifying dangers, not of redesign;
  • in lack of information, noting and proceeding to the next point.
• taking into account the different personalities of the members of the group:
  • tolerating small inconveniences and maintaining a positive and serene atmosphere;
  • keeping the most talkative people in brake;
  • soliciting the opinion of the most confidential people.
• By making use of their knowledge and experience for:
  • promote accuracy;
  • reach a point of understanding;
  • formulate the appropriate and effective recommendations.

The Secretary [ change | Modifica Wikitesto ]

The secretary must have adequate technical knowledge and actively participate in the sessions. Its tasks and characteristics are:

• maintain a level of concentration such as to allow him to grasp and write down the salient aspects of the topics under discussion;
• summarize and transcribe conclusions and recommendations formulated by the President;.
• offer support to team , for example in soliciting answers to still open questions or requests for clarifications;
• suggest any points that had been neglected and participate in the discussion, where necessary, without altering their rhythm;
• Avoid to stop the session to request clarifications on insignificant aspects.

The members of the group [ change | Modifica Wikitesto ]

The members of the working group come from the companies responsible for the design and construction and by the company by departments or units involved in the exercise and maintenance of the system in question.

Each participant represents an aspect of the necessary technical, prevention and organizational skills, as a whole, for the management of the system safely. And in this spirit that each member should participate in the study, avoiding to get his hand taken by personal or preconceptions.
The members of the team they must show (and deserve) mutual respect. When people of different seniority or career level sit around the table, younger colleagues must feel free to freely express their ideas.
Any aspects of confidentiality or confidentiality of the information must be resolved before the start of the study; The work must not be hindered, for example, by legal pressure, aimed at denying the fact that a certain incidental scenario can also cause very serious consequences on people.
Group members must maintain an open attitude and be able to recognize and describe credible accidents.
The working group must be put in a position to be able to formulate recommendations, without the need to resort to external approval.

Execution [ change | Modifica Wikitesto ]

The president leads the group to examine the various sections of the system, normally following the flow of the process.

Each session focuses on a part of the plant, delimited by the nodes chosen in advance by the president. The session begins with a brief description of the process preferably provided by the designer or by system garment (depending on the case), or if the time available is limited and his experience allows him by the president.
The main purpose of the introduction is to put all members of the team in conditions of understanding the operation of the plant section in question.
The time dedicated to the introduction must be reasonably short (5-10 minutes are generally sufficient); We must also avoid transforming this preliminary phase into a revision of the design or in a sterile discussion on the participants’ design preferences.

The president questions members of the working group through the use of keywords applied to each of the parameters of the process. The parameters are the main measurable characteristics of the system, such as: flow rate, pressure and temperature; They are systematically examined for each section of the system.
The keywords represent the main deviations, such as No , Bass , High ; They are interpreted in terms of typical events that could be at the origin of deviations compared to the project intent.
For example, in the table there are characteristic deviations for some parameters together with possible causes:

Parameter	Keyword	Typical deviation
Level	High	Malfunction of the level meter
Flow	No	Block (of a filling pipeline)
Action	Before after	The operator does not correctly perform an assembly sequence of a component
Containment	Partial	Loss
Voltage	high	Loss of insulation towards higher voltage line
Utility	Partial	Loss from the Cutting Emulsions Distribution plant

The questions asked by the President aim to stimulate the discussion regarding how deviations can occur from the project intent and if they bring to danger conditions.
In addition, the leader can formulate the question explicitly or use a combination of parameters and guidance words: in any case the basic idea is to make sure that all possible deviations are explored and potential dangers are not neglected.
For each deviation, the team It must decide whether it can happen in the plant section considered and if so assetive if it can give rise to a dangerous situation.
In cases where a deviation leads to dangerous conditions, the team Consider if there are already preventive or protective measures and proposes improvements or changes that it considers advantageous to implement.

The secretary takes note of the discussion by noting each parameter and key word pair or noting only the deviations that are the basis of a dangerous situation and for which improvement recommendations have been proposed.

The close application of all “key parameter-parameter-parameter” can be very expensive in terms of time. It is up to the president (leader) to decide an appropriate level of detail.

Normally, the key parameters are measurable variables typical of the process, which must be adapted to the system in question.

Process industry	Electrical systems	Mechanical systems
Flow	Voltage	Force
Pressure
Temperature
Level
Composition
State
Contamination
Corrosion
Chain
Resistence
Impedance
Couple
Speed
Acceleration
Pasta

The leader defines and communicates to the group the list of parameters that will be used during the study. The chosen parameters are revised and agreed before the start of the sessions.
Similarly, the choice of keywords will be linked to the process parameters to be examined.
The keywords are applied by referring to the normal conditions of operating the system.

Typical keyword	Parameter	Typical deviation
No	In the current	Inadvertently open switch
Bass	Low couple	Sliding clutch
High	High pressure	Pressostat faulty
Inverse	Reverse flow	Rupture of conduct upstream
Partial	Partial level	Loss of containment
Like (of state)	new phase	Presence of condensation
Different from	Composition	Toxic residues on product
Before after	Operator action	Wronty assembly sequence
Soon late	Control system	Delayed drive of the arrest system

However, conditions of anomalous operation are also considered, such as normal stop, start -up, emergency stop, maintenance.
In addition to the application of the crossed key parameters/keywords, the team It can also consider specific fault methods.

Loss of containment

• Pipe loss due to corrosion or mechanical impact
• Flag loss and connections
• Loss from valves or pump holding
• Refreshment of pressure container
• I waste from diametro smacks, instruments, and spurs.

General service failures

• Air and nitrogen
• Energy
• Cooling water, steam
• Fuels and fuels

Meteorological phenomena

• Lightning, wind, flooding
• Earthquake

Other specific keywords can be used to solicit the discussion on critical activities for the management of the system safe.

Tests

• Appliances and systems such as alarms, blocks and set-point of safety valves
• Sampling and analysis of finished or intermediate products.

Maintenance

• Accessibility and possibility of interception
• Drainage and purge
• Cooling or heating of equipment
• Availability of spare parts.

Electrical systems

• Electric classification of the system
• Isolation and ground.

Instruments

• Suitability/reliability/number
• Location, ways of failure and effects on majority logic systems
• Alarms, hierarchy and possibility of response from the operators.

Personnel protection

• Typical personal protection devices (DPI) (safety shoes, helmet, glasses, gloves, etc.)
• Antigas masks and self -resurreists (for potential exposure to toxic substances, entry into confined spaces, etc.)
• Work permits and prescriptions (escape routes, harnesses, etc.)
• Protection tools (oxygen analyzers, S02, CO, etc.)

Protection of plants

• Smoke and flame detectors
• Toxic or flammable detectors
• Fire -fighting systems (water, foam, etc.)
• Passive fire prevention protection
• Storage, transfer and use of chemicals
• Protections against unwanted access.

Cleaning

In many cases, the nature of the process involves the exposure of operators and plants to a series of risks, which can be identified and analyzed during the study, such as those reported for example in the following table.

Phase in Hazop	Action of the leader	Specific example	Input of the working group
Application of the parameter/keyword combination	Select: flower flow	How can the (reverse) flow in the power line take place?	In case of upstream pressure fall
Identification of a credible cause for the deviation	Explore if and how the deviation can happen	What can cause pressure fall?	1) Mount -up line breakdown 2) Valve closure 3) pump failure
Examination of the possible consequences	Check if the consequence is dangerous	There could be a danger in case of loss from the line	It depends on entities and location of the loss, the possibility of triggering and exposure of the staff
Discussion on existing maintenance protections	Check if and how the danger is controlled	How is the system protected compared to this eventuality?	Design standard Regular inspections Intervention of the emergency team

There may be more than one cause at the origin of a certain deviation and each of them must be analyzed.
The fact that the team or not recognizes the existence of a dangerous condition depends on the specific situation under examination. For example, the team may recommend the installation of a non -return valve to minimize the event of reverse flow.

Recording [ change | Modifica Wikitesto ]

Each line of the Hazop table ends with one or more of the following four types of sentences:

• A note (N): simply to record how the system works or to describe existing control measures considered adequate.
• A recommendation (R): in cases where the team agrees on the opportunity to propose an intervention aimed at improving the safety and/or performance of the system.
• A question (Q): When the information available during the Hazop is not enough and further data must be collected.
• One response (a): relating to a asked question. Where the answer identifies the existence of a dangerous condition, it can follow a further recommendation.

The Hazop document is sequentially numbered to facilitate the drafting of the subsequent action plan (for example: N1, R2, Q3, A4).
The recommendations proposed by team of Hazop aim to improve the safety and/or performance of the plant through the reduction of frequencies or consequences of unfavorable events.

Recommendations may concern many technical or organizational aspects:

• More reliable and resistant equipment and materials
• Components or tools in stand-by
• Greater frequency of tests/controls on equipment, tools and protection systems
• Review of operating procedures or intensification of training

At the end of the study it is appropriate to classify the recommendations in order of importance, as a support for the decision regarding the implementation times.

• Kletz, Trevor, Hazop and Hazan , 4th Edition, Taylor & Francis, 2006, ISBN 978-05252525-506-2.
• Tyler, Brian, Crawley, Frank & Preston, Malcolm, HAZOP: Guide to Best Practice , 2nd edition, icheme, rugby, 2008, ISBN 978-0-85295-525-3
• IEC 61882 2001 Hazard and operability studies (HAZOP studies) — Application guide