Techniques for Safety Improvements

Mr. R. R. Diwanji

Searching for hazards

 

Intuitive methods

Inductive Methods  Key points check lists  Failure mode and effect analysis  Decision Table Technique  Incident sequence Analysis  Hazard and Operability Studies (HAZOP)  Action Error Analysis  Deductive methods •The Fault Tree Techniques

Hazard Study

• 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.

How do I carry out HAZOP ?

•Assemble a team of min-3 and max 5 people •Experts required from  Process  Maintenance  Design  R&D  Safety •Safety personnel acts as a study leader •Focus on Guidewords

Guidewords

Key words Meaning Comments NO NOT MORE LESS AS WELL AS PART OF SOME OF NOT REVERSE complete failure increase or reduction qualitative increase qualitative decrease the logical opposite of the intention Not even part of the intentions or functions is achieved.

Can refer to quantities or qualities, e.g. throughput, temperature, as well as to functions like “heating “ or “react with” In addition to the intended function some unintended functions takes place Only part of the intentions or functions are achieved.

mostly applicable to functions (e.g. reverse flow, wrong sequence) OTHER THAN complete substitution Intention or function is not achieved, something quite different happens.

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

Flow Level Transfer

POSSIBLE PARAMETERS

Pressure Viscosity Control PH Sequence Time Start / stop Temp Mixing Phase Maintain Addition Part. Size Speed Signal

SUPPLY OF CHLORINE -Example

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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/cm 2 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.

II.

Collection of Basic data Physical / Chemical / Toxicity / Reaction data.

Safe condition / Limitations III. Systematic search for the hazard.

IV. Analysis of hazard according to severity& probability V. 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.

When to investigate?

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.

Who should investigate?

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

Root Cause analysis

There may be many reasons why an accident occurs.

Review Define Problem Diagnose all Causes Identify Solutions Implement Diagnose Symptoms Identify Solutions

How a root Cause Analysis is done?

    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

Structure of RCA

 The analysis must be initiated within 24 hours  Root Cause Analysis must be done by a team  Adequate Representation from various functions  Written Report to be prepared  Immediate causes (symptoms) & Root (underlying) Causes to be identified  Action Plan to prevent recurrence to be prepared

Advantages:

   a structured method to identify all possible causes of an accident to seek a preventive solution