Mr. R. R. Diwanji

Techniques for Safety Improvements

Searching for hazards

Intuitive methods Inductive Methods

Key points check listsFailure mode and effect analysisDecision Table TechniqueIncident sequence AnalysisHazard and Operability Studies (HAZOP)Action Error Analysis

Deductive methods•The Fault Tree Techniques

• Developed by ICI

• Six Stages of Study

Study 1 - To identify the basic hazard of material and operation.

Study 2- To identify the significant hazard at the project definition stage and determine the appropriate design features.

Study 3- This is hazard & operability study (HAZOP). To identify hazards operability problems after project / plant is designed.

Hazard Study

Study 4- Before introduction of process material proper checks are introduced for the hazard identified in study 1 to 3.

Study 5- To check whether project meets company & Legislative requirements

Study 6- Performed after 3 - 6 months of continuous operation the checks introduced after hazard study 1 to 4 are properly functioning.

Hazard Study

How do I carry out HAZOP ?

•Assemble a team of min-3 and max 5 people

•Experts required fromProcessMaintenanceDesignR&DSafety

•Safety personnel acts as a study leader

•Focus on Guidewords

Guidewords

Key words Meaning Comments

NONOT

completefailure

Not even part of the intentions or functions is achieved.

MORELESS

increase orreduction

Can refer to quantities or qualities, e.g. throughput,temperature, as well as to functions like “heating “ or “reactwith”

AS WELL AS

PART OFSOME OF NOT

qualitative increase

qualitativedecrease

In addition to the intended function some unintended functionstakes placeOnly part of the intentions or functions are achieved.

REVERSE

OTHER THAN

the logical oppositeof the intention

completesubstitution

mostly applicable to functions (e.g. reverse flow, wrongsequence)

Intention or function is not achieved, something quite differenthappens.

HAZOP -A STEP by STEP APPROACH

1. Select a line from P& I diagram.2. Explain intention of the line.3. Apply first guideword.4. Develop meaningful deviation.5. Examine possible causes.6. Examine consequences.7. Detect the hazard.8. Make suitable record.9. Write corrective actions

POSSIBLE PARAMETERS

Flow Pressure Temp Mixing

Level Viscosity Phase Addition

Transfer Control Maintain Part. Size

PH Sequence Speed Signal

Time Start / stop

SUPPLY OF CHLORINE -Example

•Proposal- Supply of Chlorine gas from caustic soda plant to chlorination unit at M. C. B. Plant.

•Define Intention- To supply dry pure chlorine gas at 1 to 1.5kg/cm2 pressure at the rate of 200 to 250 5kg/hr. to chlorination unit at M.C.B. plant.

•Apply Guideword to - Dry, Pure, Pressure, Rate etc.

Application

• Mainly used for continuous plant operation.Eg. Distillation columns, Complex automatic Plants, Critical parts of the system

Advantages of HAZOP Study

• Structured process• Improves operability • Moderator supports systematic procedure.

Disadvantages of HAZOP Study

Higher time commitment (mainly for larger systems)

Considers Technical aspects mainly only normal operation but start up - shut down procedures

Assumes previous analysis of chemical process risks

RISK ANALYSIS & PROCESS SAFETY

• Developed by CIBA- Geigy for searching hazard using check list

•What is Hazard?

The possibility of undesirable event that could take place

•What is risk?

Evaluation of hazard in terms of probability & Severity

Sources of Hazard

Chemicals themselves

Chemical reactions

Energies used for the process

Installations (Equipments).

Sources of Deviation

Technical defects

Human Error

System Error

How do I carry out Risk Analysis?

I. Collection of Basic data Physical / Chemical / Toxicity / Reaction data.II. Safe condition / Limitations III. Systematic search for the hazard.IV. Analysis of hazard according to severity& probabilityV. Listing of Risks.VI. Suggesting measures.VII. Residual risk.

Sample Check List

1. Process conditions• What happens if wrong R.M. is charged?• What happens if sequence of R. M. is charged?• What happens if rate of R.M. charge increases or decreases?• What happens if temperature is high?• What happens if pressure increases etc?

2. Interruption in Utilities• Power Failure• Cooling Failure• Heating Failure• Nitrogen Failure

Application

Mainly to the batch process.

Auxiliary plants with manual operators

Checking of process.

Start up shut down procedures.

Advantages

Screening procedures

Relatively less time required for data collections.

Gives a first quick overview.

Disadvantages

Additional investigations may be required for data collections.

No fully developed check lists available for complex process.

Accident Investigation

Why accident investigation?- To determine the cause of accident and not to identify scape goat.- Uncovering problems that did not directly lead to the accident.- On going effort to reduce likely hood of accident.- Prevent similar accidents in future.

As soon as all emergency procedures have been completed.Reason being - More likely to get more accurate information.

-Information becomes fade in people’s mind. -Likelihood of accident scene may get changed. -Human nature encourages people to change their

stories with those of other witnesses.

When to investigate?

- Minor injury the supervisor of injured person - Team should be consist of - Plant I/C, - Safety personnel, - Maintenance man and- Immediate supervisor.

Who should investigate?

Root Cause analysis

There may be many reasons why an accident occurs.

Define Problem

Diagnose all Causes

Identify Solutions Implement

Review

Diagnose Symptoms

Identify Solutions

Define the problem / incident accurately Ask the question “WHY did the problem occur”? List down all possible causes as you brainstorm Keep asking a series of “WHY” for each cause until the

most fundamental cause is identified Event Tree or Fish bone techniques can be used to

pictorially represent all causes Highlight all root causes Prioritize them Implement actions to prevent recurrence of the root causes Fix the problem for ever

How a root Cause Analysis is done?

The analysis must be initiated within 24 hoursRoot Cause Analysis must be done by a teamAdequate Representation from various functions

Written Report to be preparedImmediate causes (symptoms) & Root (underlying) Causes to be identified

Action Plan to prevent recurrence to be prepared

Structure of RCA

a structured method to identify all possible causes of an

accident to seek a preventive solution

Advantages: