1 chemical process safety read chapter 24: turton’s design book (crowl & louvar) chapter 11:...

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Chemical Process SafetyRead Chapter 24: Turton’s Design Book

(Crowl & Louvar)Chapter 11: Hazard Identification

Chapter 12: Risk Assessment

Guidelines for Hazard Evaluation Procedures, 3rd Ed., CCPS (John Wiley), 2008:

5.3; 7.0-7.5; ch 9

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Introduction

Micro and mini scale reactors

Adiabatic calorimeters

Kinetics,modelling,simulation

Design reappraisal,relief systems, dump and

quench tanks

Desktopstudies

Objective is to move from the earliest phases of research and development through tofull scale production in a confident, safe and cost effective manner

AutomatedCalorimetersand reactors

HAZOP,HAZAN,HAZID

Syntheticorganic

chemistryideas

Desktopscreening,databases,

calculations

Discovery research and

multipleexperiments

Automatedlaboratoryreactors.Process

optimization

Pilot plantstudies

Scale upand design

Industrial production.Debottlenecking.Optimization of

mature processes.Retrofits.

SAFE PROCESS DEVELOPMENT

C H E M I C A L P R O C E S S L I F E C Y C L E

D. Crowl, notes

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Figure 11-1 Hazards identification and risk assessment procedure. (Adapted from Guidelines for Hazards Evaluation Procedures (New York: American Institute of Chemical Engineers, 1985), pp. 1–9.)

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Process Hazard Analysis – Many Options

1. What-If2. Checklist3. What-If/Checklist4. FMEA – Failure Mode & Effects

Analysis 5. FTA – Fault Tree Analysis6. Hazards Surveys7. HAZOP – Hazards & Operability

study

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Process Hazard Analysis – Many Options

1. What-If2. Checklist3. What-If/Checklist4. FMEA – Failure Mode & Effects

Analysis 5. FTA – Fault Tree Analysis6. Hazards Surveys7. HAZOP – Hazards &

Operability study

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1. What-If Analysis

• Unstructured method for considering results of unexpected events

• Uses questions beginning with "what-if“• Not concerned with "how" failures occur• Purpose is to identify problems that could

lead to accidents• Results in a list of potential problem areas

and suggested mitigation methods

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What-If Example

LNG Vaporizer

What if:

(a) Water flow is stopped?(b) LNG flow is stopped?(c) Natural gas temperature is too low?(d) Water flow is too low?(e) Water pressure is too high?(f) A tube leaks into the shell?(g) Inlet water temperature is too low?

D. Crowl, notes

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What-If ExampleLNG Vaporizer

too low?

flow alarm.

What-If Consequence/ Hazard Recommendation

Water flow is stopped? Water in shell freezes and may rupture shell; natural

gas temperature too low.

Automatic interlock to

stop LNG flow if water

flow is stopped.

LNG flow is stopped? Not Hazardous None

Natural gas temperature is

Downstream piping may become embrittled.

Monitor gas temperature; low temperature alarm.

Water flow is too low? Natural gas temperature

may be too low; water may

freeze in tubes.

Monitor flow rate; low

D. Crowl, notes

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6. Hazards Surveys

Can be simple like inventory of hazardous chemicals

More rigorous procedures:

- Dow Fire & Explosion Index

- Dow Chemical Exposure Index

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6. Hazards Surveys: Dow Fire & Explosion Index

• Complex and detailed procedure carried out by an individual• Rates relative hazards of storing, handling, processing flammable and explosive materials• Systematic approach independent of judgmental factors

• Break the process down into units or sections, e.g. the reactor, storage tank or a pump

• Use experience to select the units or sections that have the highest likelihood of a significant hazard (too many to cover all); may use checklist approach to choose

• Define the material factor (what chemicals are being used); in general, higher the value the more flammable / explosive

• Adjust this with various penalties based on conditions such as storage above normal boiling point, exothermic reaction, etc

• Then take credits for safety procedures and safety systems• Finally arrive at a number that rates the hazard; compare with table /

experience

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Dow Fire & Explosion Index standard form; C&L Fig 11-3

Penalties Material factor

Penalty factors

Special ProcessHazards Factor

MF

F1

General ProcessHazards Factor

F2

D. Crowl, notes

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Dow F&EI - Determining the degree of hazard, Table 11-2

F&EI index value Degree of hazard

1 – 60 Light 61 – 96 Moderate 97 – 127 Intermediate 128 – 158 Heavy > 158 Severe

D. Crowl, notes

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7. Hazard and Operability (HAZOP) Study

HAZOP is a Structured "What If" Type of Study• Objectives

- Identify Hazards

- Identify Operability Problems• HAZOPs Use Team Approach• Multi-Disciplinary• Guide word based• Structured and Systematic

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Hazards and Operability Study

Investigative Process• Select study nodes

– Major process vessels– Major process lines connected to process vessels– Pumps and compressors– Heat exchangers– Major support systems

• Pick a process parameter

- Flow, level, temperature, pressure, volume, pH, concentration, agitation, etc

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Investigative Process (Cont’d)

• Apply guide words to process parameters– Determine deviation from design– Determine consequences of deviations– Evaluate consequences

• Typical causes of deviations– Hardware failures– Human error– Outside forces– Unanticipated process state

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Investigative Process (Cont’d)• Suggested actions

– Change in design– Change in equipment– Alter operating procedures– Improve maintenance– Investigate further

• HAZOP Follow-up– Assign responsibility for carrying out recommendations with

agreed timetable– Refer recommendations to appropriate managers– Evaluate and review

• Record keeping– Copy of all data used– Copy of all working papers– HAZOP worksheets

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Guide Words and Their Meanings

Simple words or phrases used to qualify the intention and associated

parameters in order to discover deviations.Guide Words & Symbols

Application to Input Material Application to Desired Activity Further Applications

Design Intent The intended material including quantity, chemical composition and input physical condition.

The intended activity. May be one major and one or more dependent minor activities.

Further intentions, e.g., sources or destination.

NO The intended material is not present but no substitute material present.

The intended activity does not occur but no direct substitute activity takes place.

MORE A greater quantity of material than intended, e.g., "Higher Pressure".

A greater activity than intended, e.g., flow rate, pressure rise, heat input, chemical reaction, duration of activity etc.

LESS A lesser quantity of material than intended, e.g., weight or volume. Lower physical condition, e.g., "Lower Pressure".

A lesser activity than intended, e.g., flow rate, pressure rise, heat input, chemical reaction, duration of activity etc.

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HAZOP Example

• Chemistry is such that concentrations of B must not exceed that of A

• First Study Node - pipeline from suction side of pump that delivers A to the reaction vessel

• First Guide Word - No to design intent of transfer A • Causes of Deviation

– Supply tank is empty – Pumps fail to run – Pipeline is fractured – Isolation valve is closed

• Consequences – Excess of B over A could lead to an explosion

• Recommendation – Install interlock device on pump B into reactor

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HAZOP Example Worksheet

D. Crowl, notes

21W. Buck, SDSMT Seminar, 2012

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Risk Matrix

B.K. Vaughen, PSM Overview, SACHE, 2012

Freq

uen

cy

Consequence

UnacceptableUndesirable Marginal

Risk = F x C

Acceptable

Negligible Marginal Serious Critical Catastrophic

Frequent D C B A A

Probable D D B B A

Occasional D D C B B

Remote D D D C B

Improbable D D D D C

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Risk Equation


Frequency x ConsequenceRisk =

Operational Discipline

Frequency x ConsequenceRisk =


Frequency

How often the event may occur

- its likelihood is a “probability”

Consequence

How severe the event may be

- an undesired result of the event

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The personal commitment of everyone to ensure

their

personal and process safety by

1) performing their tasks correctly, and

2) recognizing, responding to and seeking

help, as needed, to unanticipated situations

or conditions.

OD

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“Organizational” OD

Leadership Focus

Employee Involvement

Practice Consistent With

Procedures

Excellent Housekeeping

“Personal” OD

Awareness

Knowledge

Commitment

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Risk Reduction


F x CRisk =

OD

F Frequency

Engineering and Administrative Controls

C Consequence

Inherently Safer Processes

Emergency Response

Design

Phase: the

best time to

use ISP

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Risk Reduction


OD Operational Discipline

Safety Culture Organizational OD

Safety Behavior and Personal OD

Commitment Characteristics

F x C Risk =

OD

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Effect of Poor OD on Risk


Fre

quen

cyConsequence

Negligible Marginal Serious Critical Catastrophic

Frequent D C B A A

Probable D D B B A

Occasional D D C B B

Remote D D D C B

Improbable D D D D C

Unacceptable

Undesirable

Marginal

Actual Risk

Perceived Risk

Risk = OD

F x C

Acceptable

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Risk Matrix

W. Buck, SDSMT Seminar, 2012

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PSM Systems


Designed to minimize process safety risk:

There is always some level of risk

Our PSM-related risk reduction efforts are compared and

evaluated against other potential business risks (i.e.,

environmental, operational, maintenance, quality and

financial)

Risk = OD

F x C

32B.K. Vaughen, PSM Overview, SACHE, 2012

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Questions?

1 chemical process safety read chapter 24: turton’s design book (crowl & louvar) chapter 11:...

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