7/27/2019 hazopcas

1/21

Safety

Use Case Histories to

Energize YourHAZOP

7/27/2019 hazopcas

2/21

Glenn E. Mahnken,

Reviewingincidentreportsat a

FM Global

Photos:

2000 Factory

Mutual Insurance

Company. Reprinted

with permission.T

he process safety management

pro-grams of many companiesincludeformal process hazardsanalyses,using methods such as hazardandoperability (HAZOP) studiesandwhat-if reviews, as keyelements

o

f

H

A

Z

O

P

m

e

et

in

g

is

m

or

e

th

a

n

just a

lessons

learned

activity. It

can spur

sharper

thinking

and lead

to a

more

telling

analysi

s of

your

proces

ses.

likely to

discover the

unforeseen

effects that

might result in

a preventable

major accident.

As noted, the

team is

working with a

basically sound

design, so the

sought after

effects are

often quite

subtle. To find

as many of

these as

possible, the

team mustenergetically

probe and

challenge the

process design

and be able to

sustain its

efforts over

many hours of

questioning and

answering.

7/27/2019 hazopcas

3/21

Safety

7/27/2019 hazopcas

4/21

7/27/2019 hazopcas

5/21

Table 2. Selected case histories from the AIChE Loss Prevention Symposia (1971 2000).

Author(s) Title Year Incident type Consequences

R. C. Dartnell,Jr.

Explosion of a Para-Nitro-

1971

Unexpected thermal degradation ofPNMC

and T. A.Ventrone Meta-Cresol Unit

caused the rupture of a 3,000 gal stainlesssteelstorage tank into five pieces inside abuilding.

A. H. Searson Fire in a Catalytic 1971 Corrosion as a result of a process changeled to

Reforming Unitrupture of piping and release ofhydrocarbons.

T. J. R.Stephenson Explosion of a Chlorine

1972

Hydrogen formed in a corrosiveenvironment

and C. B.Livingston Distillate Receiver where Cl

over into the process where Cl

was high. The vapors ignited due tounknown

ignition source.

T. A. Kletz Case Histories on197

3Maintenance was underway to add abranch

Loss Preventionline to a steam main, which had notbeenadequately isolated from a process ventprior to welding.

T. A. KletzEmergency IsolationValves

1975 Gasket on a level connection for a

for Chemical Plants reactor burst suddenly, allowing therelease of polypropylene vapor, whichignited after about 20 min, probably duetobuildup of static electricity in the cloud.

S. A. SaiaVapor Clouds and Firesin

1976 During shutdown due to power failure,

a Light HydrocarbonPlant a 24 in. bellows expansion joint failed,

allowing 15,000 gal of polypropylene totoescape. Vapor cloud traveled 250300ftto furnaces and ignited within about 2min.

A. L. M. Explosion in a Naphtha 1977Upsets during startup caused highlevel/low

vanEinjnatten Cracking Unittemperature in a feed drum, resulting incoldbrittle fracture of a weld. Loss ofcontainment

of polypropylene. Vapor cloud ignited.

V. G. GeishlerMajor Effects fromMinor

1978

Power failure caused control valves toshut.

Features in EthylenePlants

Thrust forces on pipe caused controlloopsupports to puncture the pipe, resultingin

loss of containment of flammable liquid.

Fire, explosion damage to building, injuries,one fatality.

Vapor cloud explosion and major fire, injuries.

Chlorine receiver blew apart into five pieces, also

causing extensive damage to nearby equipment.

When the welder cut into the steam main, anexplosion occurred.

Despite 4,0005,000 gpm water deluge, the fire spread

to neighboring units causing considerable material

damage.

Sprinkler systems contained the fire toTrain 2.

14 fatalities, 106 injuries.

Fire, property damage, business interruption.

T. A. Kletz Organisations Have NoMemory

S. J. SkinnerExplosive Evolution ofGasin Manufacture of EthylPolysilicate

D. R. PesuitDust Explosions inStorageSilos: Polyvinyl Alcohol

R. E.Sanders Plant Modifications

Troubles and Treatment

T. O. Gibson Learning Value from aRecent Loss

D. J. Lewis A Review of SomeTransportation Accidents,Identification of Causes

Operat

or

opene

d the

door to

a

pressu

re filter

that

was

still

underpressu

re.

Reactan

ts

had

diffe

rent

den

sitie

s

and

did

not

mix

initi

ally.

Gas

bub

bles

evol

v

e

d

b

y

r

e

a

c

t

i

o

n

a

7/27/2019 hazopcas

6/21

t interface caused mixing and

runaway acceleration of the

reaction.

Electrostatic discharge during

unloading of polymer from a tankertruck into a silo. Operation had

operated without incident for manyyears.

No flow of oil when a processheater was fired up and the

safeguards had been field-adjusted out of range.

Electrical fault in an indoor

transformer containing 235 gal of

mineral oil.

High pressure caused a cryogenic

ethylene tanker truck to explode. It

was parked near an alcohol

unloading rack. The cause was

considered to be freezing of the

safety relief valve.

Operatorwaskilled.

Cov

er

was

blow

n off

the

reac

tor

and

the

plant

was

enve

lope

d in hydrogen

chloride fumes.

Explosion: silo

swung over in

flames onto the

top of the truck

and the transfer

line.

6 in. dia. tube

ruptured andallowed 1,800gal of oil toescape. Fireensued andcausedsubstantialproperty

damage.

Oil fire

spread to

electrical

cables and

into the

control

room.

Caused

emergency

evacuation

of thecontrol

room. A

$17.6 million

loss.

The

tanker

rocket

e

d

.

A

l

c

o

h

o

l

f

i

r

e

.

Vaporcloudexplosion.

74 www.aiche.org/c ep/ March 2001 CEP

7/27/2019 hazopcas

7/21

7/27/2019 hazopcas

8/21

Author(s) Title Year Incident type Consequences

P. G. Snyder Brittle Fracture of a High1987

Pressure HeatExchanger

R. F. Schwab Explosion and Fire at a1988

Phenol Plant

T. O. Gibson Learning Value from a1989

Blown Fuse

B. W. Bailey Iron Fire in Heat1990

Recovery Unit

S. E.

Anderson More Bang for the Buck:

19

91and R. W.Skioss Getting the Most from

Accident Investigations

D. J. LeggettManagement of aReactive

1992

Chemicals Incident:Case Study

M. L. Griffinand Case Histories of Some

1993

F. H. Garry Power and Control-basedProcess Safety Incidents

W. E. Clayton

and Catastrophic Failure of a

19

94M. L. Griffin Liquid Carbon Dioxide

Storage Vessel

R. E.Sherman,

Carbon-initiated EffluentTank

1995

K. C.Crawford, Overpressure IncidentT. M. Cusick,andC. S.Czengery

S. Mannan Boiler Incident Directly1996

Attributable to PSM

Issues

D. S. Hall andCarbon DisulfideIncidents

1997

L. A. Losee DuringViscose RayonProcessing

F. P. Nichols Air Compressor Delivery1998

Pipeline Failure

H. L. FeboPlastics in Construction

1999

The Hidden Hazard

Y. Riezel Fixed Roof Gas-Oil Tank2000

Explosion

Combination of

deviations lead to

brittle fracture at

3,400 psig during

hydrostatic

pressure testing of

a steam generator

following an

outage.

Hightemperature

as a result of

a leaking

steam valve,

in

conjunction

with

abnormal

conditions

that arose

during

process

restart,

caused

explosion of

a 25,000 gal

tank

containing

cumene

hydroperoxid

e.

Blown fuse in

instrumentation

power supply

caused series of

abnormal

conditions,

including high

condensate level

in a steam drum,

which overflowed

into the steam

header.

Condensate was

introduced into a

hot 20 in. dia. line

when a steam

valve was opened.

Hightemperaturesoccurred as aresult of anelectricalshort incontrol wiring

while gasturbine wason turninggear. Theshort causedfuel valves toopen andignitiontransformer toenergize.

Hightemperature andrunawayreaction

occurredin a railtank carcontainin

galoadofmethacryli

cacidthatwasinsufficientlyinhibited

.

Wrongmaterialwasloadedin

toachemicalb

arge

7/27/2019 hazopcas

9/21

.

High gas flow to a reactor resulted when an air-to-open valve suddenly went to the full open position (asa result of a plugged orifice in the valve positioner).

High temperature occurred in a tank containing 30 m.t. CO2,when an internal heater failed "on." The high temperatureresulted in high pressure. The relief valve on the tank failed toopen.

High temperature (hot spot) developed in a carbonbed absorber connected to the vent line of a 1,000

bbl intermediate effluent storage tank.

Low water level occurred in a high-temperature boiler in

a process plant due to failure to follow proper

procedures and failure of the low-level interlock.

High level of carbon disulfide liquid during a cleaning operation

resulted in overflow into the heating zone and sudden

volatilization of the liquid.

Low flow of air from one of the cylinders of a double-acting

reciprocating air compressor resulted in high temperature and

concentration of lubricating oil mist in the air stream.

High temperature occurred in the plastic duct andscrubber due to loss of quenching for the hot fluegases when a pulp mill recovery boiler trippedoffline and interlocks failed.

More hydrogen was present than was expected inthe gas-oil stream sent from a hydrogendesulfurizing unit to a

15,000 m3

storage tank.

No injuries. Refinery

production was

curtailed to 6070%

for 4 mo.

Phenol Unit 1 was almost

completely destroyed by

fire. Severe damage to

adjacent Unit 3. Fuel tank

fire.

The line ruptured.Three people weresprayed with steamand condensate. Twofatalities.

Fuel gas burnedinside thecombustor exhaustduct. The 600 psigheat recovery unitcaught fire and wasdestroyed.

Car exploded. Parts

were found 300 yards

away. Overhead

electrical lines were

severed, shutting

down production.

Incompatible reactive

chemicals mixed. 48

72 h state of alert.

Near miss.

Gas vented into

the area ofthe reactor.

The tank exploded.Three fatalities,$20 millionpropertydamage, 3 mo.lost production.

The vent streamwas in the

flammable range,

ignited and

propagated back

to the storage

tank. The tank

roof was blown off

(~200 ft).

The boiler was

dry fired.

Serious internal

damage to

boiler and

steam drum. No

injuries (nearmiss).

Explosion blew

out a wall.

Extensive fire

in the ductwork.

Minor injuries.

The air stream

ignited and an

explosion

propagate

d a

"galloping

detonation

" in the

compresse

d air

pipeline.

All plastic

duct work

destroyed,

scrubbercollapsed

onto

cable tray.

Mill was shut

down for

extended

period.

Property

damage over

$5 million.

The tank

exploded

as a result

of

electrostatic

discharge

during a

sampling

operation.

One fatality.

Massive fire

in storage

dike.

CEP March 2001www.aiche.org/ce p/

75

7/27/2019 hazopcas

10/21

Safety

Table 1. Case history synopsis hypothetical HAZOP worksheet (in hindsight).

Company: ABC Study-Section: 2.1 SVG piping: fan to incinerator Facility: XYZPlant

HAZOPDate:

Process: Waste Gas IncineratorLeader/Scribe:

Design Intent: Burn AOG and SVG off-gases

TeamMembers:

HAZOP

Deviat

ion Cause ConsequencesEngineering/

F*

C*

R* Questions/

ItemNo.

Administrative Recommendations

Controls

2.1.1Noflow Valves L and K (1) Increase Operators 2 1 D 2.1.1.1

closedimproperly concentration of follow Check procedures for Valves L and K

combustiblegases

proceduresfor Are procedures clearly documented?

in SVG piping. shutdowns.Do procedures cover abnormalsituations?

(2) Potential High 2 4 B 2.1.1.2

explosion if gasconcentration Check gas alarm response time

goes into

explosive alarm. is it fast enough?range and gasreachesincinerator.

7/27/2019 hazopcas

11/21

Bypass SVG 2.1.1.3

to flare on Check bypass response time vs.high: highgas travel time to incinerator.concentrationalarm.Flamearrestor. 2.1.1.4

Review flame arrestor design vs.

expected blast pressures.

Damage-limiting 2.1.1.5

construction. Review flame arrestor design vs.

expected reaction forces.

* F = frequency; C = consequence severity; R = risk ranking.

How case histories can helpClearly, a variety of psychological factors come into play

that can encourage or hold back the HAZOP team duringdeliberations (2). The intent is to help encourage criticalthinking by making short presentations of previous chemical

process industries (CPI) plant accidents to the team (3). Of

course, as a general prerequisite for the suc-cess of anyHAZOP, the participants must already own the process (4),i.e., the team members must have a strong sense of urgencyand be highly motivated by virtue of their roles andresponsibilities as process designers, plant engi-neers,supervisors, operators, and technicians. In this con-text, casehistory presentations can be made at the start of a meeting, or

during a break to help engage and galvanize the team bytelling a short war story and, at the same time,demonstrating the connection between HAZOP guidewordsand real world accidents.

The immediate benefit of the case history presentation is not

quantifiable in terms of the HAZOP output; one sim-ply

surmises that a properly designed 10-minute presenta-tion can be

worthwhile, because a group with an accident example fresh in

their minds will be more critical and more creative in their

deliberations through the course of the study. A long-term

benefit, assuming case history presenta-tions become an integral

part of the plants HAZOP ses-sions, is that participants will

gradually accumulate a body of loss experience and invaluable

loss-prevention wisdom

based upon reported CPIplant losses. This benefit isnot quantifiable either; itrelates to the value oflearning any kind of historythat we desire to avoid

repeating. In this re-spect,the HAZOP session affordsa unique opportunity topresent these history lessonsto busy engineers and plantpersonnel who generally arenot easy to assemble forsuch purposes.

Use a synopsispresentation format

HAZOP meeting time is

almost inevitably in short

sup-ply. And, since the main

intent of presenting the casehisto-ry is not to study the

details of the accident, but

rather to help energize the

critical thinking process, a

synopsis pre-sentation format

is most appropriate. In the

context of the study,

providing the basic sequence

of events of the acci-dent,

along with a flow schematic,

selected loss lessons and key

conclusions will suffice as

long as these are offered in a

manner that engages the

interest of the team. The pre-

sentation can also include a

hypothetical HAZOP work-sheet page that illustrates how

the accident might have been

foreseen in a HAZOP study.

This worksheet serves as a

minitraining example for new

participants and a refresher

for those with previous such

experience. Of course, the

reasons for making the case

history presentation also need

to be explained to the group

at the start of the

presentation.

The person presenting the

case history need not be the

group leader or the same

individual. Team members

can take

76 www.aiche.org/cep/ March 2001 CEP

7/27/2019 hazopcas

12/21

Figure. 1. Source slide.

Case History Synopsis

Based on the paper:

Flashback from Waste Gas Incinerator

into Air Supply Piping

S. E. Anderson, A. M. Dowell, III, P.E.,

and J. B. Mynaugh

Rohm and Haas Texas, Inc.P.O. Box 672

Deer Park, TX 77536

Paper 73c prepared for presentation at the

25th Annual AIChE Loss Prevention

Symposium, August 18-22, 1991

Figure 2. Summary slide.

Accident Summary1 Miscommunication between outside

operators and control room resulted in closing the

wrong valve

2 A waste gas incinerator experienced a

flashback with a pressure wave in the supply piping

3 Damage to flame arrestor, piping, fan, and theincinerator

7/27/2019 hazopcas

13/21

Waste Gas AOGWaste Gases

Incineratorfrom Process

Valve L

Vent Gases(SVG)

from Process

Valve KSVG Fan

To SVG FlareFigure 3. Schematic slide.

Figure 4. Process slide.

Process Description

1 Waste gas incinerator burns off-gases

from two separate sources: AOG and SVG

2 SVG stream is normally routed to the waste gas

inciner-ator at less than 10% of the lower explosive limit

(LEL)

3 At 25% LEL, an alarm sounds

1 At 50% LEL, the SVG stream bypasses to theflare

Figure 5. Cause slide.

7/27/2019 hazopcas

14/21

Initial Cause

1Field operators misunderstood radio instructions

from the control room to close the AOG valve to the

incinerator

2 Valve L was closed by mistake and Valve K

was being opened

3 SVG was blocked in: VOCs increased

4 Valve L was then reopened, sending theSVG to the incinerator, which flashed back

Figure 6. Consequences slide.

Consequences (Partial list)

7/27/2019 hazopcas

15/21

1 SVG flame arrestor was broken from its

mounting bolts and sheared into 2 pieces

2 Stainless steel piping connecting the SVG

flame arrestor to SVG fan was broken free from itssupports and came to rest on top of the fan

3 Explosion was not stopped by the flamearrestor

4 Incinerator had numerous radial

cracks in the refractory brick

5 SVG piping going up to reactor rack fell

from the third level to the ground

6 Plastic (FRP) piping connected to the SVG

fan suction was sheared and broken

7 Missile damage to incinerator bustle

8 The manual wheel for Valve K was broken

off at the gear box casing

9 No injuries But, at the time of the

explosion, an operator was holding onto thewheel for Valve K

Figure 7. Conclusions slide.

Some Conclusions

1 Unusual circumstances of human factors,

unsteady-state events, and a rapid challenge com-

bined to overcome the well-designed safety systems.

2 Much of the serious damage was the

result of poor construction.

1 Consult the original paper for additional

findings and many recommendations that havegeneral application for this type of equipment.

CEP March

2001www.aiche.org/ce

p/ 77

7/27/2019 hazopcas

16/21

Safety

7/27/2019 hazopcas

17/21

7/27/2019 hazopcas

18/21

7/27/2019 hazopcas

19/21

A fire could

cost you ...

turns being

assigned a case

history as

prework to

study before the

meeting, and,using already

pre-pared

overhead slides

or handouts,

make the pre-

sentation to the

rest of the team

at a convenient

break in the

meeting. The

original case

history ar-ticle

should

preferably be

familiar to the

presenter

beforehand, but

discussion of

the accident

details should

be minimal.

The original

article can be

made available

to interestedparticipants for

fol-lowup

reading outside

of the meeting.

Examplepresentation

A well-

known case

history paper

describing a

waste-gas-incinerator

explosion at a

chemical plant

was presented

at the 25th

annual AIChE

Loss Prevention

Symposium

(5). As

described in the

original paper,

the accident

evolved as fol-lows: The

AOG process,

which

supplied

one of

the two waste gas

streams feeding into

an incinerator, shut

down safely and

tripped offline. The

incinerator remained

in operation,

burning waste gas

from a second

process, called

SVG. In preparing

the AOG line for a

restart, op-erators

accidentally closed

the wrong valves,

resulting in the SVGgas flow being

blocked in. The

control room oper-

ator received a low

SVG flow alarm and

radioed to the field

operators to reopen

the SVG valve to the

incinerator. The

SVG flow to the

incinerator was

quickly restored and

an explosion

occurred, resulting

in overpressure

damage to the

incinerator

refractory, as well as

the dislocation of

pip-ing, valves, a

flame arrestor, and

the main SVG

blower. Fortunately,

there were no

injuries to theoperators who were

working in the

vicinity of the

explosion.

Liter

atur

eCit

ed

1.Kletz, T., Hazop

and Hazan:

Identifying and

Assessing Process

In-dustry Hazards,

4th ed., Taylor &

Francis, London, p.

34 (1999).

2.Leathley, B., and

D. Nicholls,

Improving the

Effectiveness of

HAZOP: A

Psychological

Approach,Loss

Prevention

Bulletin, Issue No.

139, p. 8 (1998).

3.Mahnken, G., et

al., Using Case

Histories in PHA

Meetings, Paper

6c, presented at

AIChE 34th

Annual LossPrevention Sympo-

sium, Atlanta (Mar.

69, 2000).

4.Kletz, T., Hazop

and Hazan:

Identifying and

Assessing Process

In-dustry Hazards,

4th ed., Taylor &

Francis, London, p.

33 (1999).

5.Anderson, S. E., et

al., Flashbackfrom Waste Gas

Incinerator intoAir

Supply Piping,

Paper 73c, AIChE

25th Annual Loss

Prevention

Symposium,

Pittsburgh (Aug.

1821, 1991).

6. Loss Prevention

on CD ROM,

AIChE, New York

(1998). The set

contains

presentations from

all 31 Loss

Prevention

7/27/2019 hazopcas

20/21

Symposia spon-sored by

AIChEs Safety and

Health Division from

1967 to 1997, plus early

CCPS conference and

workshop proceedings

from 1987 through 1994.

(See

www.aiche.org/pubcat.)

7.Kletz, T., What Went

Wrong: Case Histories of

Process Plant Dis-asters,4th ed., Gulf Publishing,

Houston (1998).

8. Sanders, R. E.,

Chemical Process Safety:

Learning from Case His-

tories, Butterworth

Heineman, Boston (1999).

more thanyou know.

A synopsis ofthis accident,prepared in a slide

format intended forpresentation toHAZOP groups, isgiven in Figures 1through 7. Table 1represents ahypotheticalHAZOP worksheetthat predicts the

accident (in perfecthindsight, of course). Theworksheet attemptsto demon-strate tothe team how, by

using criticalthinking and fol-

lowing HAZOPmethodology, theymight have beenable to identifysome of thepossible causes andconsequences, aswell as develop thecorresponding

action items to helppre-vent or mitigate

an actual accident.

Sources ofaccident casehistory reports

The annual

AIChE Loss

Symposium Papers

(6) include many

accident case history

studies that are

detailed and, often,

written first hand by

the accidentinvestigators or par-

ticipants. Table 2 is

a selected list of

these reports from

19712000 that can

be used in the

manner described

above. Other sources

are available as well,

such as case history-

based loss

prevention books (7,

8), loss preventionjournals, e.g., the

Loss Prevention

Bulletin, and

published investiga-

tive reports. A good

source of these

reports is the U.S.

Chemical Safety and

Hazard Investigation

Board, Washing-ton,

DC. The CSB allows

downloading of itsinvestigation

reports at www.csb.gov.

C

E

P

T

o

j

o

i

n

a

n

o

n

l

in

e

d

i

s

c

u

s

s

i

o

n

a

bo

u

t

7/27/2019 hazopcas

21/21

t

h

i

s

a

r

t

i

c

l

e

wi

t

h

t

h

e

a

u

t

h

o

r

an

d

o

t

h

e

r

r

e

a

d

e

r

s,

g

o

t

o

t

h

e

P

r

o

c

e

s

sC

i

t

y

D

i

s

c

u

s

s

i

o

n

R

o

o

m

f

o

r

C

E

P

a

r

ti

c

l

e

s

a

t

w

w

w

.

p

r

o

c

e

ss

c

i

t

y

.

c

o

m

/

c

e

p

.

7. E. MAHNKEN

is a loss prevention

specialist with FM

Global (formerly known

as FactoryMutual),

Norwood, MA ((781)

440-8000 ext. 8644;

Fax: (781) 440-8718; E-

mail:

glenn.mahnken@fmglo

bal.com). He has been

with the company for 15

years, and holds a BA

in biology from Antioch

College and a BS in

chemical engineering

from the National

Technical University of

Athens, Greece. He is a

member of AIChE.

78

www.aiche.org/cep/

March 2001 CEP