hazard operability analysis

8/9/2019 hazard operability analysis

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HAZOP STUDY

CHAPTER No.11

HAZOP STUDY

INTRODUCTION

A HAZOP survey is one of the most common and widely accepted methods of systematic

qualitative haard analysis! "t is used for #oth new or e$istin% facilities and can #e applied

to a whole plant& a production unit& or a piece of equipment "t uses as its data#ase the

usual sort of plant and process information and relies on the 'ud%ment of en%ineerin% and

safety e$perts in the areas with which they are most familiar! The end result is& therefore

relia#le in terms of en%ineerin% and operational e$pectations& #ut it is not quantitative and

may not consider the consequences of comple$ sequences of human errors!

The o#'ectives of a HAZOP study can #e summaried as follows(

)* To identify +areas of the desi%n that may possess a si%nificant haard potential!

,* To identify and study features of the desi%n that influence the pro#a#ility of a

haardous incident occurrin%!

-* To familiarie the study team with the desi%n information availa#le!

.* To ensure that a systematic study is made of the areas of si%nificant haard

potential!

/* To identify pertinent desi%n information not currently availa#le to the team!

0* To provide a mechanism for feed#ac1 to the client of the study team2s detailed

comments!

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Production of Acrylonitrile


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HAZOP STUDY

A HAZOP study is conducted in the followin% steps(

)* Specify the purpose& o#'ective& and scope of the study! The purpose may he the

analysis of a yet to #e #uilt plant or a review of the ris1 of un e$istin% unit!

3iven the purpose and the circumstances of the study& the o#'ectives listed

a#ove can he made more specific! The scope of the study is the #oundaries of

the physical unit& and also the ran%e of events and varia#les considered! 4or

e$ample& at one time HAZOP2s were mainly focused on fire and e$plosion

endpoints& while now the scope usually includes to$ic release& offensive odor&

and environmental end5points! The initial esta#lishment of purpose& o#'ectives&

and scope is very important and should #e precisely set down so that it will #e

clear& now and in the future& what was and was not included in the study! These

decisions need to #e made #y an appropriate level of responsi#le mana%ement!

,* Select the HAZOP study team! The team leader should #e s1illed in HAZOP

and in interpersonal techniques to facilitate successful %roup interaction! As

many other e$perts should #e included in the team to cover all aspects of

desi%n& operation& process chemistry& and safety! The team leader should

instruct the team in the HAZOP procedure and should emphasie that the end

o#'ective of a HAZOP survey is haard identification6 solutions to pro#lems

are a separate effort!

-* 7ollect data! Theodore)0 has listed the followin% materials that are usually

needed(

Process description

Process flow sheets

Data on the chemical& physical and to$icolo%ical properties of all raw

materials&& intermediates& and products!

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HAZOP STUDY

Pipin% and instrument dia%rams +P8"Ds*

9quipment& pipin%& and instrument specifications

Process control lo%ic dia%rams

:ayout drawin%s

Operatin% procedures

;aintenance procedures

9mer%ency response procedures

Safety and trainin% manuals

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HAZOP STUDY

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HAZOP STUDY

Table-11.2: HAZOP Guide Words and eanin!s

Guide Words eanin!

uantitative increase

>ualitative decrease

>ualitative "ncrease

:o%ical opposite of the intent

7omplete su#stitution

.* 7onduct the study! Usin% the information collected& the unit is divided into

study ?nodes? and the sequence dia%rammed in 4i%ure & is followed for each

node!


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HAZOP STUDY

/* rite the report! As much detail a#out events and their consequence as is

uncovered #y the study should #e recorded! O#viously& if the HAZOP

identifies a not impro#a#le sequence of events that would result in a disaster&

appropriate follow5up action is needed! Thus& althou%h ris1 reduction action is

not a part of the HAZOP& the HAZOP may tri%%er the need for such action!

The HAZOP studies are time consumin% and e$pensive! Bust %ettin% the P 8 "D2s

up to date on an older plant may #e a ma'or en%ineerin% effort! Still& for processes with

si%nificant ris1& they are cost effective when #alanced a%ainst the potential loss of life&

property& #usiness& and even the future of the enterprise that may result from a ma'or

release!

HAZOP "#ud$ o% "#ora!e Tan& %or Pro'$lene

A HAZOP study is to #e conducted on Propylene stora%e tan1& as presented #y the pipin%and instrumentation dia%ram show in fi% +)C!,*!

"n this scheme& propylene is unloaded from tan1 truc1s into a stora%e tan1

maintained under a sli%ht positive pressure until it is transferred to the process!

Application of the %uide words to the stora%e tan1 is shown in Ta#le +)C!,* alon% with a

listin% of consequences that results from process deviation! Some of the consequences

identified with these process deviations have raised additional questions that need

resolution to determine whether or not a haard e$ist!

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HAZOP STUDY

148


Propylene

Storage Tank


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HAZOP STUDY

Figure-11.2: Pi'in! and ins#ru(en#a#ion dia!ra(

Deviations

fromoperatin%

conditions

hat event could causethis deviation

7onsequences of this

deviation on item ofequipment under

consideration

Processindications

:evel(

:ess

;ore

Temperature(

:ess

;ore

Tan1 runs dry

=upture of dischar%e line

@5- open or #ro1en

@5) open or #ro1en

Tan1 rupture +#ustin% of

vessel*

Unload too much from

column

=everse flow from

process

Temperature of inlet is

colder than normal

Temperature of inlet is

hotter than normal9$ternal fire

Pump cavitates

=ea%ent released

=ea%ent released

=ea%ent released

=ea%ent released

Tan1 overfills

Tan1 overfills

Possi#le vacuum

=e%ion released

Tan1 fails

:"A5)

4"7A5)

:"A5)&

4"7A5)

:"A5)

:"A5)

:"A5)

:"A5)

:"A5)

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