TOPIC : SAFETY ANALYSIS & PREVENTIONDATE : June 2014LECTURE : DETAILED HAZARD ANALYSIS,

RISK ANALYSIS and ManagementLecturer : Dr Ghulam Murshid (GM)

Health, Safety &Environment (CCB 2012)

Lecture Content Part 2 Detailed Hazard Analysis

Failure mode and effect analysis (FMEA) Hazard and operability (HAZOP) Fault tree analysis (FTA) Risk analysis (RA)

You should be able to identify, defineand differentiate Detailed Hazard Analysis (for complex system)

Failure mode and effect analysis (FMEA) Hazard and operability review (HAZOP) Human error analysis (HEA) Fault tree analysis (FTA) Risk analysis and Management

Lecture Outcome

Proceeds as follows: Critically examine the system in question. Divide the system into its various components. Each component is studied to determine how itcould fail.

Rate each potential failure according to itsconsequences (0 to 10).

Failure mode and effect analysis (FMEA)

Weaknesses: no human error factor. does not account for component interfaces.

FMEA Example

HAZOP HAZOP highlights include: Systematic examination Multidisciplinary study Utilization of operational experience Safety as well as operational evaluations May indicate solutions to the identified

problems Considers operational procedures Led by an independent person Results are recorded.

Preparation for HAZOP Detailed information on the processmust be available

Process flow diagrams (PFD), processand instrumentation diagrams(P&Ids), detailed equipmentspecifications, materials ofconstruction and mass & energybalances are very essential for thestudy.

Process Flow Diagram (PFD)

HAZOP Guide WordGuide words describe ways in which the component maydeviate from its design.

No Less More Part of As well as Reverse Other than

Never none Quantitative decrease Quantitative increase Qualitative decrease Qualitative increase Opposite of forward Complete substitution

Guide words Meaning

Stages of HAZOP as applied to eachcomponent of a chemical processing systemare described below:1. Identify the design intent of the selected partof process.2. Consider each condition or action using theHAZOP guide word to suggest possibledeviations3. Consider causes and consequences of thedeviation4. Define and note the action required to addressthe problems.

Procedure

EXAMPLEThe phosphoric acid and ammonia are mixed,and a non-hazardous product, diammoniumphosphate (DAP), results if the reaction ofammonia is complete. If too little phosphoricacid is added, the reaction is incomplete, andammonia is produced. Too little ammoniaavailable to the reactor results in a safe butundesirable product. The HAZOP team isassigned to investigate "Personnel Hazardsfrom the Reaction".

SOLUTIONStorage A

Storage B

Reactor C Storage C

Valve A

Valve B

Parameter Deviation Possible Causes Consequences Action

Flow NO flow into reactor Blockage or leaking pipe into R Rate of reaction decreases

No reaction occurring

Install flow indicator and flow

control valve

NO flow out of reactor Reactor outlet clogged or

blocked

No flow to subsequent

separation units

Stop operation

Perform reactor maintenance

MORE Control valve failure trim

changed

Exchanger tube leaks

Incorrect instrument readings

Reactants build-up

Increase in reaction rate

Check flow indicators and

controllers

By-pass flow

LESS Blockage or leaking in piping

system into R-100

(line restriction)

Reduced rate of reaction

Less production

Install flow indicator and

controllers

HAZOP

Parameter Deviation Possible Causes Consequences Action

Pressure MORE Reactants build-up

Blocked pipeline

Pressure indicator failure

Pressure build-up inside

reactor

Runaway reaction

Install high pressure alarm

Pressure relief system (PRV)

LESS Leakage in piping of reactor Reduced reaction rate

Reverse flow

Check feed pressure

Install Pressure indicator at

feed to reactor

Temperature MORE Higher reaction rate

Excess feed into reactor

Cooling system failure

Feed heater failure

R-100 out of control

Runaway reaction

Catalyst deactivation

Install high temperature alarm

Install coolant flow meter and

low flow alarm

Perform maintenance on feed

heater

LESS Low feed temperature

Feed heater failure

Low reaction rate

Low product purity

Increase feed temperature

Install temperature indicator

Human Error Analysis (HEA)

It is best to perform HEA together witheither FMEA or HAZOP. This will enhancethe effectiveness of all three processes.

For predicting human error before accidents occurby:

observing employees at work and notinghazards.

actually performing job tasks to get a first handfeel for hazards.

FTA The analysis process is displayed visually. Between Basic event and Top Event. Uses symbols derived from Booleanalgebra.

The resultant model looks like a logicdiagram or a flow chart.

Fault Tree Analysis (FTA)

OR gate

AND gate

Top eventIntermediateevent

Basic event

Undevelopedevent

External orhouse event

TransferIN-OUT

Logic and Event Symbols

Top Event ContributingEvents

Undeveloped Event Basic Event

The FaultTree

Concept

FaultTree Fault tree: top-down approach startingwith the unwanted consequences as thetop event & identifying all factors thatcould contribute to the top event.

Used to think through possible causesof a loss, to find most probablesequence of events leading to the loss& to quantify the probability of loss.

Steps: FTATo draw a fault tree take the followingsteps.1. Determine undesirable event, which is to be the Top

Event.2. Determine the Basic Events, which could immediately

cause the Top Event.3. Determine the relationship between the Basic

Events and the Top Event in terms of AND and ORgates.

4. Determine whether any of the Basic Events needfurther analysis, if so repeat steps 2 & 3.

Example: Fault TreeConsider a case of a motor overheated. TheBasic Events could be the primary motor failsor excessive current load to the motor.The current load might be excessive due toexcess current flow in the circuit and failure ofthe fuse.It could be either short circuiting or a powersurge that contributed to the excess currentflow.

Example: Fault TreeMotor OverheatedPrimaryMotorFailure

A

FuseFails

B

ExcessiveCurrent to

Motor

ExcessCurrent In

Circuit

Shortcircuit

C

PowerSurge

D

AND

OR

OR

The probability of the Top Event (themotor overheated) is obtained bycombining the base events accordingto the logic rules:

For this case, probability= [(C+D) x B] + A

For an OR gate (ADD theprobabilities)

For an AND gate(MULTIPLY the value)

Example: Fault TreeMotor OverheatedPrimaryMotorFailure

0.05

FuseFails

0.1

ExcessiveCurrent to

Motor

ExcessCurrent In

Circuit

Shortcircuit

0.007

PowerSurge

0.003

AND

OR

OR

The probability of the Top Event(the motor overheated) isobtained by combining the baseevents according to the logicrules:

For this case, probability

= [(0.007+0.003) x 0.1] + 0.05

= 0.051

Risk Analysis (RA) Decision-making tool normally associatedwith insurance and investments. It can also be used to analyse theworkplace, identify hazards and developstrategies for overcoming hazards. Focuses on TWO questions:

How frequently does a given eventoccur? How severe are the consequences of agiven event?

What is a risk?Risk may be considered as the potential foradverse effects resulting from an activity orevent

Acceptable level of riskThis is generally determined by what isprepared to be lost balanced against possiblegains

The Risk Management ProcessThe total procedure associated with

identifying a hazard,

assessing the risk,

putting in place control measures,

and reviewing the outcomes.

Hazard IdentificationRemember Hazard:

Risk Assessment

Risk Control

Risk AssessmentRisk:The possibility of an unwanted eventoccurring

Likelihood:The chance of an event actually occurring.

Likelihood Very Likely -- Could happen frequently

Likely -- Could happen occasionally

Unlikely -- Could happen, but only rarely

Highly Unlikely -- Could happen butprobably never will

When evaluating the likelihood of an accident,a factor that will modify the likelihood category, is

exposure.

Very Rare -- Once per year or less Rare -- A few times per year Unusual -- Once per month Occasional -- Once per week Frequent -- Daily Continuous -- Constant

Likelihood

ConsequencesFATAL Death

MAJOR INJURIES Normally irreversible injury ordamage to health requiring extended time off work to effectbest recovery.

MINOR INJURIES Typically a reversible injury ordamage to health needing several days away from work torecover. Recovery would be full and permanent.

NEGLIGIBLE INJURIES Would require first aid and mayneed the remainder of the work period or shift off beforebeing able to return to work.