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Sunday, May 26, 2013

HIRARC: HAZOP



HAZOP is an acronym for HAZard and OPerability studies. The term 'HAZOP' originated in ICI and first appeared in the literature in the early 1970s.


Skelton, B, (1997) defined it as a formal, systematic, critical, rigorous examination to the process and engineering intentions of new and existing facilities to assess the hazard potential of mal-operation or mal-function of individual items of equipment and the consequential effects. Wells, G, (1996),  HAZOP is formal, systematic examination of a processing plant in order to identify hazards, failures and operability problems, and assess the consequences from such mal-operation.

HAZOP will generates a list of identified problems, usually with some suggestions for improvement of the system. It will  improves safety, reliability and quality by making people more aware of potential problems. It also will help to sort out loopholes and inconsistencies
in procedures and force plant personnel to get their instructions up to date.

Basic philosophy of HAZOP; if a process operates within its intended design philosophy then undesired hazardous events should not occur. The objective of a HAZOP is mainly to identify how process deviations can be prevented or mitigated to minimize process hazards.

Basic Ideas of HAZOP are to stimulate the imagination of a review team, including designers and operators, in a systematic way so that they can identify potential hazards in a design; AND to let the mind go free in a controlled fashion in order to consider all the possible ways that
process and operational failures can occur.

Outcomes of HAZOP; to recommend necessary changes to a system to meet company risk guidelines, AND to recommend procedures or changes for eliminating or reducing the probability of operating deviations.

HAZOP used as an application at the correct stage in a project means that problems are identified and can be rectified during detailed design. It will provide a considerable amount of useful material for inclusion in the plant operating instructions.

HAZOP Terminology; (1) Design intent - the way in which the plant is intended to operate. (2) Deviation - any perceived deviations in operation from the design intent. Cause - the causes of the perceived deviations. (3) Consequence - the consequences of the perceived deviations. (4) Safeguards - existing provisions to mitigate the likelihood or consequences of the perceived deviations and to inform operators of their occurrence, (5) Actions - the recommendations or requests for information made by the study team in order to improve the safety and/or operability of the plant. (6) Guide words - simple words used to qualify the intent and hence discover deviations. (7) Parameters - basic process requirements such as 'flow', 'temperature', 'pres-sure' and so on.

HAZOP COMPONENTS are Team, Procedure and Guide words. HAZOP Team normally comprises between four and eight members,  each of whom can provide knowledge and experience appropriate to the project to be studied. The team needs to be small enough to be efficient and allow each member to make a contribution, whilst containing sufficient skills and experience to cover the area of study comprehensively.

Two types of person are required in a Hazop team: those with detailed technical knowledge of the process; AND those with knowledge and experience of the HAZOP technique and the ability to chair and report upon technical meetings.

typical member of a Hazop team are chairman or team leader, secretary, process design engineer, control engineer, operations specialist and project engineer. Other specialists may be consulted or be available for specific points.

Chairman or team leader is selected for his or her ability to effectively lead the study. He/she should have sufficient seniority to give the study recommendations the proper level of authority and has a knowledge and experience of the Hazop technique.

Secretary should have a technical appreciation of the project and be familiar with the HAZOP technique. The technical members are usually part of the project design team.

Hazop PROCEDURE

1. Begin with a detailed flow sheet. Break the flow sheet into a number of process units.  eg the reactor area might be one unit, and the storage tank another. Select a unit for study.
2. Choose a study node (vessel, line, operating instruction).
3. Describe the design intent of the study node. eg example, vessel V-I is designed to store the benzene feedstock and provide it on demand to the reactor.
4. Pick a process parameter( flow, level, temperature, pressure, concentration, pH, viscosity, power, Inert and etc.
5. Apply a guide word to the process parameter to suggest possible deviations.(NO, MORE, LESS, REVERSE and etc)
6. If the deviation is applicable, determine possible causes and note any protective systems.
7. Evaluate the consequences of the deviation (if any).
8. Recommend action: what, by whom, by when.
9. Record all information.
10. Repeat steps 5 through 9 until all applicable guide words have been applied to the chosen process parameter.
11. Repeat steps 4 through 10 until all applicable process parameters have been considered for the given study node.
12. Repeat steps 2 through 11 until all study nodes have been considered for the given
section and proceed to the next section on the flow sheet.











HIRARC: FMEA



FMEA is an acronym that stands for Failure Modes and Effects Analysis. It can identifies the potential failure of a system and its effects, assesses the failures to determine actions that would eliminate the chance of occurrence and documents the potential failures.


It’s oriented towards equipment rather than process. Particularly suited for mechanical and electrical systems. FMEA systematically in identifies the consequences of component failure on that system and to  determines the significance of each failure mode with regard to the system's performance. It will improve the safety, Quality and Reliability.

The purpose of this Hazard Identification system are to identify single equipment of system failure modes and the potential effects or consequences of the failure modes on the system or plant, AND to generate recommendation for increasing equipment or system reliability, thus improving process safety.

Resource requirements to do this system are;(1) Technical drawing of the equipment / system,(2) Knowledge of equipment function and failure modes,(3) Personnel with knowledge of system /plant function and responses to failure equipment failure AND (4) Personnel with knowledge of FMEA methodology and analysis.



It also can be define as the extent of the system to be analyzed. It usually performed in relatively small steps. It requires analysts / personnel with a knowledge of the system. It will show the functional relationships of the parts of the system and their performance requirements.

Level of Analysis are based on the functional structure of a system and the failure modes are expressed as failure to perform a particular subsystem function. Primary function is that for which the subsystem was provided and secondary function is one which is merely a consequence of the subsystem's presence.

It will be use to analyze Failure modes of  premature operation, failure to operate when required, intermittent operation, failure to cease operation when required, loss of output or failure during operation, degraded output and etc. It will looks at the likely causes and the effects on both the components and the system, consideration is given to the relative importance of the effects and the sequence AND safeguards against such failures and methods of detecting them are then examined.

Reporting of FMEA are to identify the most significant failures in terms of their effects on the overall system, decide whether or not the existing safeguards and detection devices are adequate AND more detailed analysis on the ‘weak link’. There are no standard reporting format; typically covers  The unit/system, Failure mode, Consequence of failure, Symptoms, safeguards and Corrective action.


 


FMEA CRITICALITY ANALYSIS (FMEACA)

Criticality is defined in the same way as risk – that is, a combination of the severity of an effect and the probability or expected frequency. It is the simplest approach that requires a form of ranking or quantification in effect / consequence AND frequency.

Effects are normally ranked into one of the following categories; (1) loss of mission due to inability of equipment to perform,(2) economic loss due to lack of output or function, (3) damage to plant or third party property, (4) injury to operating personnel or the public, (5) death to operating personnel or the public and/or significant damage to the environment.

Quantification of frequency depends on the data available and may again be a simple ranking, such as one depending on failure probability during the operating time interval, for example; extremely unlikely, remote, Occasional, reasonably frequent AND frequent.

Alternative ranking for effect (reverse order or severity), For Example; (1) catastrophic - may cause death or total system loss,(2) critical- may cause severe injury or damage,(3) major - may cause some injury or damage AND (4) minor - requires unscheduled maintenance.







Corrective Action And Follow-up are (1) reduce probability that the cause of failure will result in the failure mode,(2) reduce severity of failure by redesign or add protection redundancy AND (3) increase probability of detection.

Thursday, May 23, 2013

HIRARC : TASK ANALYSIS



TASK ANALYSIS

Working Environment
·         Material- Flammable, Toxic, oxidizing, corrosive
·         Systems- Units, Equipments, Instruments, etc
·         Process / Operation
·         Human

Hazard Identification
·         Material- Dows FE&I, CEI, ISI
·         Systems-  FMEA, FMEACA
·         Operation / Process- HAZOP
·         Human- Task Analysis


Human at Work

Work may be done by Rule based or Skill based. Conscious behavior is being used whenever task is being learned- rule-based behavior as rules are developed on how to do the task. Unconscious behavior, generally known as skill, takes over once complete proficiency is attained.

At work people try for as long as possible to control demands on their resources using skill-based behavior- they can work for several hours without unacceptable fatigue. When the situation requires more analytical reasoning, as when incidents occur, they switch to rule-based or conscious behavior


Human Error

Past worldwide records of major accidents of industrial facilities shows that many of those accidents were caused by human error of either plant  operators or maintenance contractors(Lees, 1996). An error is often the end-point of a complex series of events involving failures associated:
·          with the process and system
·          the procedures and practices
·          communication systems
·          Etc

Error is more likely due to:
·          failure to provide adequate resources and training.
·          inadequate management and supervision
·          working conditions are not optimal,
·          pressure on the operator to make a correct
·         decision is high due to any cause
·          Unfamiliar conditions and lack of technical back-up and information

An error may be defined as the failure of planned actions to achieve their goals. Error:
·          Violations
·          Mistakes
·          Slips
·          Mismatched

TERMINOLOGY

Violation- an intentional departure from accepted practice.  example not wearing a hard hat.
·         a hat is hot to wear
·         it is getting in the way
·         less comfortable than being bare-headed
·         a hat may not be readily available

Slips- errors in automatic skill-based or unconscious behavior. example  Slips occur when actions are not as planned.

Mistakes;
·         errors in conscious behavior which may be either rule-based, if the task merely involves following a set of procedures, or knowledge-based when the task involves evaluation of a new situation.
·         Mistakes arise when planning is inadequate.
·         Mistakes due to lack of knowledge
·         They may lack elementary knowledge of the properties of the materials, the process or the equipment.
·         They may believe they must always follow rules, and be unable to react correctly when flexibility is needed
·         People may be given contradictory or ambiguous instructions. Also instructions may have implied contradictions

Conscious behavior is being used whenever task is being learned - rule-based behavior as rules are developed about how to do the task. Error: Mistakes. Unconscious behavior, generally known as skill, takes over once complete proficiency is attained.  Error: Slips. Intentional deviation from rules, procedures, standard practice.  Error: Violation.

Example

Ahmad drove his car southbound along PLUS highway. He was enjoying his drive at 145 km/h and was not wearing seat belt. Between Ayer Keroh R&R and Exit, he had a flat tyre. While preparing to replace the flat tyre, he found that there was no spare tyre.
·         What is the task
·         Violation??
·         Mistakes??
·         Slips??

Three pipes (A,B and C) are utilized to transfer flammable gas. Pipe B required maintenance work. An operator in the control room pressed the wrong button which isolated pipe A instead of pipe B. A team of maintenance contract workers removed a
flange connection at pipe B, flammable gas was released and ignited by one of the contractor worker who was smoking.
·          What is the task
·          Violation??
·          Mistakes??
·          Slips??

TASK ANALYSIS

A process of sorting out what people might or actually do when carying a task. The analysis try to respond to relevant questions:
·          what actions do the operators carry out?
·          how do operators respond to different cues in their environment?
·          what errors might be made and deviations caused in plant operations?
·          how might any error be recovered from, or any deviation be controlled?
·          how do operators plan their actions?

Task analysis helps in the prevention or reduction in the frequency of occurrence of error. Task Analysis has been developed as a systematic method for analyzing a task into its
·          goals
·          operations
·          Plan
·          Procedure
·          practice

A goal is what the person doing the job is aiming to achieve-  A specific work objective. A task is a specific work assignment- represents the set of operations / actions required to achieve a stated goal. The operations represent the stages involved in the task. Plans describe the methods and conditions under which the operations are carried out.

A procedure is a step-by-step description of how to proceed from beginning to end in order to perform a given task. A practice is a set of guidelines helpful to the performance of a specific type of work which may not always follow a set procedure.

Task Analysis can provide input to such features as:
·          the specification of equipment, controls, emergency controls and process interface;
·          the preparation of procedures and operating instructions;
·          the development of written practices;
·          the specification of training requirements and development of skills

Types of Task Analysis

·         Hierarchical Task Analysis (HTA) -  Graphical / Tubular representation - Decomposition of high level task into constituent subtasks, operations, plans
·         Cognitive Task Analysis -  Model the internal representation and processing that occurs for the purpose of designing tasks that can be undertaken more effectively by humans
·         Modeling how to knowledge - Focuses on task to action mapping.  GOMS approach (Goals, Operations, Methods, Selection Rules)

Example of Tubular / textual HTA

0. Clean the house
1.0 Get the vacuum cleaner out
2.0 Fixed the appropriate attachment
3.0 Clean the rooms
3.1 Clean the hall
3.2 Clean the living rooms
3.3 Clean the bedrooms
4.0 Empty the dust bag
5.0 Put the vacuum cleaner and the attachments away

Plan 0: do 1-2-3-5 in that order. When dust bag full do 4
Plan 3: do 3.1, 3.2 and 3.3 in any order depending on which rooms need cleaning


DATA FOR TASK ANALYSIS

Data / Information required
·         documentation process diagrams, functional models, job descriptions, working practices and permits, instructions, operating manuals, design specifications, existing documentation of task; . output from hazard reviews;
·          Hazard reviews
·          study of plant records, computer output, logs, etc
·          debriefing of operators following completion of the task

Information required
·          discussion or interview with management, actual or potential users, design, engineers, safety specialists and human factors experts;
·          observation, recording and inspection during operation and user trails including use or video, audio, transcripts, coding schemes.

STEPS IN CARRYING OUT A TASK ANALYSIS

Goal of the analysis;
·         The overall goal of the task to be carried out should be stated
·         Examples: To ensure adequate supply of raw materials for a processing unit
·         Task - a specific work assignment that represents the set of operations / actions required to achieve a stated goal. Examples (1) To schedule arrival of raw material supply truck; (2) To fill raw material storage tank; (3)  To pumping of raw material to processing unit

Breakdown of the task into steps or activities
·         The task is then broken down into a set of subordinate tasks or operations which must be per-formed to achieve the goal at that level
·         to list all the steps which are critical for performing the task correctly
Creating a plan
·         A plan should refer to each of its subordinate operations.
·         Plans are important in defining when to carry out various operations, their sequence, the duration of an activity, the process conditions and so on.
·          The plan might take the form of a hierarchical diagram (flow diagram) or a tabular list.
Analyzing the plan. The analysis of the plan or system should:
·         examine possible deviations from the system
·         detemine the likelihood of those deviations
·         determine any deviation at the start and end of the procedure
Modifying the plan
·         Modifications should be made to improve the method of working and to reduce the effect of deviations and appropriate controls, precautions and mitigation introduced
·         The analysis of the plan leads to improvements in such features as working methods, procedures and practices, work environment and exposure frequency, communication and information processing, skill and capabilities of people, and management, supervision and control
·         The plans should also give advice on action to take when deviations arise and recovery as necessary including such features as: (1)what to do if the transfer of material is to the wrong place or if it is off-specification; (2) how to effect immediate recovery from human error or equipment malfunction; (3) The plan must be properly documented with appropriate performance standards, practices and procedures clearly identified.
·         The plans should also give advice on action to take when deviations arise and recovery as necessary including such features as: (1) A procedure should therefore start by indicating the task purpose and features of importance; (2) Practices should present positive guidelines for correct performance.

THE STRUCTURE OF PLANS

A plan might involve several different types of method:
·          in a set or fixed sequence- the person follows a set of activities in a specific order
·          in a timesharing sequence- the operations are carried out in co-ordination with each other or at the same time
A plan might involve several different types of method:
·          in a branching sequence- the person will do a task, then depending on the outcome from that task, the individual will carry out a particular option;
·          a plan may allow for the selection of the task which is most appropriate to the situation.

Example 3

Prepare a plan for changing a flat tyre on a car. It can be assumed that the ground is level, the spare tyre is properly inflated and the car is not in a hazardous location. Each task could be expanded with respect to action if problems in performance occur.

ANALYSIS OF TASK DEVIATIONS

There are many ways of analyzing task deviations. The traditional method study approach employs (What?, When?, How?, Where?, Who?, Why?).  The objective is to improve safety, production and quality with possible savings in cost. Example of questions in analysis of task deviations?
·          Is the task to be performed within the operator's ability?
·          Does the task place excessive demands upon the operator?
·          What environmental concerns must be addressed for this task?
·          What potential emergencies can arise, and can the operator recognize them?
·          Is needed information displayed and/or available?
·          Will the operator know what to do with the information?
·          Will the operator be able to control the system?
·          Does this task require further study or decomposition?

CRITICAL TASK

Safety Risk ; SR = 2(S+ L)
·         Negative values is treated as zero
Severity: 1 to 5
Likelihood: -5 to 0
·         10-5 to 100 per year
Production Lapse
·         values range from –2 to 2
·         10-2 to 102 per year
Quality Lapse
·          Similar basis as in production lapse
Critical Task: CT=SR+PL+QL

Example 4
A batch storage tanks system for storing flammable liquid is shown in Figure1. The tank is 5 m high. Further protection and operating aids provided are:
·         Low level alarm (LAL) at 0.5 m,
·         High level alarm (LAH) at 4.1 m
·         a trip system closing valve FV2 and high high level alarm (LHH) at 4.2 m.


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