Hazard Identification

Chapter 6

Let’s think together....identify the potential hazards

Let’s think together....identify the potential hazards

Contents Introduction of Hazard Identifications Hazard and Operability Studies (HAZOP) HAZOP guidewords

Objectives Identify study nodes and decide on

possible hazards based on HAZOP guidewords

Construct HAZOP review table subsequently assess the hazard’s cause, consequence and action required.

What is Hazard Identification? Questions that must be asked for each

process in chemical plant What are the hazards? What can go wrong and how? What are the chances? What are the consequences?

Provide basic information for risk assessment

Figure 10-1 Hazards identification and risk assessment procedure

When it should be performed? At any stage during the initial design or

ongoing operation of a process. It serves to enables modifications to be

easily incorporated into the final design and to operate the ongoing process better in terms of safety.

Who should perform? It usually requires a committee which composed of cross-

section of experienced plant, laboratory, technical and safety professional

One individual must be a trained safety personnel and serves as the committee chair. He will lead the discussion and must be expert in the chemical process under review

One individual must also be assigned the task of recording the results

The meeting duration must be short enough to ensure continuing interest and input from all committee members

It takes a large investment of time and effort, but the results are well worth the effort

How to perform?

1.Process hazard checklists provide a list of items and possible

problems in the process that must be checked.

should only be applied during the preliminary stage of hazard identification and not be used as a replacement for a more complete hazard procedure.

1. Process hazard checklistsA classic example is an automobile checklist that one might review before driving away on a vacation. This checklist might contain the following items: Check oil in engine.

Check air pressure in tires.

Check fluid level in radiator.

Check air filter.

Check fluid level in windshield washer tank.

Check headlights and taillights.

Check exhaust system for leaks.

Check fluid levels in brake system.

Check gasoline level in tank.

Checklists for chemical processes can be detailed, involving hundreds or even thousands of items.

2. Hazard surveys1. Hazards surveys

It is more like to inventory of hazardous materials, or, it can be detailed as the Dow Fire & Explosion Index.

use a rating form

How to perform?3. Safety review

It is a method used to identify safety problems in laboratory and process area and to develop solutions.

Two (2) types Informal: small changes to existing processes Formal: new process, substantial changes to existing processes

4. Hazard and operability studies (HAZOP) is a formal systematic procedure used to identify hazards in

a chemical process facility very effective in identifying hazard

Hazard and Operability Studies

What is HAZOPA Hazard and Operability (HAZOP) study is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment, or prevent e cient operation.ffi

The HAZOP technique was initially developed to analyze chemical process systems, but has later been extended to other types of systems and also to complex operations and to software systems.

A HAZOP is a qualitative technique based on guide-words and is carried out by a multi-disciplinary team (HAZOP team) during a set of meetings.

When to perform HAZOP ?

The HAZOP study should preferably be carried out as early in the design phase as possible - to have influence on the design. On the other hand; to carry out a HAZOP we need a rather complete design. As a compromise, the HAZOP is usually carried out as a final check when the detailed design has been completed.

A HAZOP study may also be conducted on an existing facility to identify modifications that should be implemented to reduce risk and operability problems.

When to perform HAZOP ?HAZOP studies may also be used more extensively, including:

At the initial concept stage when design drawings are available

When the final piping and instrumentation diagrams (P&ID) are available

During construction and installation to ensure that recommendations are implemented

During commissioning

During operation to ensure that plant emergency and operating procedures are regularly reviewed and updated as required

Type of HAZOP Process HAZOP

The HAZOP technique was originally developed to assess plants and process systems Human HAZOP

A “family” of specialized HAZOPs. More focused on human errors than technical failures Procedure HAZOP

Review of procedures or operational sequencesSometimes denoted SAFOP - SAFe Operation Study

Software HAZOPIdentification of possible errors in the development of software

For identifying causes and the consequences of perceived mal operations of equipment and associated operator interfaces in the context of the complete system.

Objective of HAZOP

Identifies potential hazards, failures and operability problems. Recommended as a principal method by professional

institutions and legislators on the basis of proven capabilities for over 40 years.

Most effective as a team effort consists of plant designers, operating personnel, control and instrumentation engineer etc.

Encourages creativity in design concept evaluation. Results in fewer commissioning and operational problems and

better informed personnel, thus confirming overall cost effectiveness improvement.

Why & How HAZOP Is Used?

For preliminary HAZOP Process Flow Sheet

(PFS or PFD) Description of the

Process

What is needed to perform HAZOP?

For Detailed HAZOP Piping and Instrumentation

Diagram ( P & ID ) Process Calculations Process Data Sheets Instrument Data Sheets Interlock Schedules Layout Requirements Hazardous Area

Classification Operating instructions

1. Detailed flow sheet, break into process units, select a unit2. Choose study node (vessel, line, operating instruction)3. Describe the intent of study node (vessel: to store)4. Pick a process parameter: flow, level, temperature, pressure, etc.5. Apply guide words to generate deviations from normal operation

corresponding to all conceivable possibilities such as NO or NOT, MORE, LESS, AS WELL AS, PART OF, REVERSE, OTHER THAN.

6. If deviation is applicable, determine possible causes and note any protective systems

7. Evaluate consequences8. Recommend actions9. Record information

HAZOP Procedures

Process flow for HAZOPSelect Line

Select deviation (eg. MORE flow)

Is more flow possible?Move on to next deviation

Is it hazardous or does it prevent efficient operation?

Will the operator know that there is more flow?

What changes in plant or method will prevent the deviation or make it less likely or protect against the

consequences?

Is the cost of the change justified?

Agree change(s), who is responsible for action

Consider other causes of more flow

What change in plant will tell him ?

Consider other changes or agreed to accept hazard

Follow up to see action has been taken

Choices of lines – P&ID must be divided logically, not too many sections

Factors to be considered: Each section should contain active components,

which gives rise to deviations. E.g piping which contains control valves can give rise to flow deviations, heat exchangers can cause T deviations.

Materials in section – contain significant amount of hazardous materials.

Section based on process and states of materials. Only one process operation per section.

Guidelines for Division into Sections

General guidelines: Define each major process component as a

section. Usually anything assigned equipment number should be considered a major process component.

Define one line section between each major process component.

Define additional line sections for each branches off the main process flow.

Define a process section at each connection to existing equipment.

Guidelines for Division into Sections

Supplementary guidelines Define only one process section for equipment

in identical service. However, pumps in different service with a common spare must be treated separately.

Define only one line at the end of a series of components if there are no other flow paths.

Define only one additional line section if there are alternative flow paths, regardless of how many branches there are.

Guidelines for Division into Sections

Do not define line between major equipment items if there are no single active components that could cause deviations.

Do not define sections for existing equipment that is upstream of new or modified equipment. Address malfunctions of such upstream equipment as deviations in the new or modified equipment.

Guidelines for Division into Sections

Guide WordsNONE No forward flow when there should be

MORE More of any parameter than there should be, e.g more flow, more pressure, more temperature, etc.

LESS As above, but "less of" in each instance

PART System composition difference from what it should be

MORE THAN More "components" present than there should be for example, extra phase, impurities

OTHER What needs to happen other than normal operation, e.g. start up,shutdown, maintenance

Guide WordsNONE e.g., NO FLOW caused by blockage; pump

failure; valve closed or jammed : leak: valve open ;suction vessel empty; delivery side over - pressurized : vapor lock ; control failure

REVERSE e.g., REVERSE FLOW caused by pump failure : NRV failure or wrongly inserted ; wrong routing; delivery over pressured; back- siphoning ; pump reversed

MORE OF e.g., MORE FLOW caused by reduced delivery head ; surging ; suction pressurised ; controller failure ; valve stuck open leak ; incorrect instrument reading.

Guide WordsMORE OF MORE TEMPERATURE, pressure caused by

external fires; blockage ; shot spots; loss of control ; foaming; gas release; reaction;explosion; valve closed; loss of level in heater; sun.

LESS OF e.g., LESS FLOW caused by pump failure; leak; scale in delivery; partial blockage ; sediments ; poor suction head; process turndown.

LESS e.g., low temperature, pressure caused by Heat loss; vaporisation ; ambient conditions; rain ; imbalance of input and output ; sealing ; blocked vent .

PART OF Change in composition high or low concentration of mixture; additional reactions in reactor or other location ; feed change. 

Guide WordsMORE THAN Impurities or extra phase Ingress of

contaminants such as air, water, lube oils; corrosion products; presence of other process materials due to internal leakage ; failure of isolation ; start-up features.

OTHER Activities other than normal operation start-up and shutdown of plant ; testing and inspection ; sampling ; maintenance; activating catalyst; removing blockage or scale ; corrosion; process emergency ; safety procedures activated ; failure of power, fuel, steam , air, water or inert gas; emissions and lack of compatibility with other emission and effluents.

The application of each guide word to a process line to generate all conceivable deviations must be thorough and exhaustive.

For each deviation generated the cause and the consequences must be determined . Typical questions which could arise are: Do we need a high liquid level alarm as well as a level

indicator? Is a single non-return valve sufficient ? Is the vent big enough ?

Guide Words

HAZOP Study Report Form

Project Date Sheet 1 of 12

Process Section

GUIDE WORDS

DEVIATION

CAUSES CONSEQUENCES

ACTIONS, OR RECOMMENDATIONS

HAZOP Study Form

Table 10-6 (page 451)

Systematic, reasonably comprehensive and flexible suitable mainly for team use whereby it is possible to

incorporate the general experience available gives good identification of cause and excellent

identification of critical deviations use of keywords is effective and the whole group is

able to participate excellent well-proven method for studying large plant

in a specific manner identifies virtually all significant deviations on the

plant, all major accidents should be identified but not necessarily their causes.

Strengths of HAZOP

Time consuming and can be laborious with a tendency for boredom for analysts

Tends to be hardware-oriented and process-oriented, although the technique should be amenable to human error application

Tends to generate many failure events with insignificance consequences and generate many failure events which have the same consequences

Stifles brainstorming although this is not required at the late stage of design when it is normally applied

Does not identify all causes of deviations and therefore omits many scenarios.

Weaknesses of HAZOP

Takes little account of the probabilities of events or consequences, although quantitative assessment are sometime added. The group generally let their collective experiences decide whether deviations are meaningful

Poor where multiple-combination events can have severe effects

Tends to assume defects or deterioration of materials of construction will not arise

When identifying consequences, HAZOP tends to encourage listing these as resulting in action by emergency control measures without considering that such action might fail. It tends to ignore the contribution which can be made by operator interventions

Weaknesses of HAZOP

Exothermic reaction controlled by cooling water

HAZOP Example

TC

Cooling Coils

MonomerFeed

Cooling Water to Sewer

Cooling Water In

Thermocouple

Description of the process The reaction is exothermic. A cooling system is provided

to remove the excess energy of reaction. In the event of cooling function is lost, the temperature of reactor would increase. This would lead to an increase in reaction rate leading to additional energy release. The result would be a runaway reaction with pressures exceeding the bursting pressure of the reactor. The temperature within the reactor is measured and is used to control the cooling water flow rate by a valve.

Perform the HAZOP study on this unit to improve the safety of the process

HAZOP study as in Table 10-7 (page 453) : handout

HAZOP Example

See the Figure. An alkene / alkane fraction containing small amounts of suspended water is continuously pumped from a bulk intermediate storage tank via a half-mile pipeline into a buffer / settling tank where residual water is settled out prior to passing via a feed / product heat exchanger and preheater to the reaction section. The water, which has an adverse effect on the dimerization reaction, is run off manually from the settling tank at intervals. Residence time in the reaction section must be held within closely defined limits to ensure adequate conversion of the alkene and to avoid excessive formation of polymer.

Node is flow in pipe

Throughout the study Should be an integral part of an overall

safety management system Process must have full backing and support

of senior management

Factors for a Successful HAZOP Study

Before the study Must be initiated by a person with authority, who will

receive and implement the actions The design must be well developed and firm,

drawings must be well prepared Skilled and suitably experienced team leader should

be chosen Team must be balanced and well chosen to combine

knowledge and experience

Factors for a Successful HAZOP Study

During the study Team must be motivated and have adequate time to

complete the task The boundary of the study must be clearly analyzed and

studied Must have clear process description, design intent and

design envelope The study uses a creative thought process. Should fatigue

sets in, study must be halted and resumed when the team is refreshed

Factors for a Successful HAZOP Study

After the study Every action raised must be analyzed and

answered accurately Those which require a positive change

should be subject to a management of change process

Factors for a Successful HAZOP Study

Hazard identifications is one of the most important tasks for a process plant

HAZOP is a mature and most popular tool for identifying hazards without waiting for an accident to occur

Summary

Thanks…..

aziz

an

ram

li2010