1b_bhopal.ppt
-
Upload
jayan-perkasa -
Category
Documents
-
view
7 -
download
1
Transcript of 1b_bhopal.ppt
Bhopal located in North Central India
Very old town in picturesque lakeside setting
Tourist centreIndustry encouraged to go to
Madhya Pradesh as part of a policy to bring industry to less developed states
Annual rent $40 per acreDecision by Union Carbide in 1970
to build was welcomed
Bhopal Capitol ofMadhya Pradesh
The Setting
Operator : Union Carbide India Ltd.Half owned by Union Carbide USA (50.9%)Plant built to produce carbonyl pesticide :
SEVIN-DDT substituteVery successful initially - part of India’s
Green RevolutionInitial staff 1000
The Plant
Initially in quiet suburb
Later the town expanded around it
Attracted a large squatter camp, as in many third world countries
The Surroundings
SEVIN manufactured fromCarbon Monoxide (CO) imported by truck
Monomethylamine (MMA)
Chlorine (Cl2) made on site
Alpha-Napthol (AN)
Process route
CO + Cl2 COCl2 (Phosgene)
COCl2 + MMA MMC + MIC
MIC stored in three 15,000 gal tanks
MIC + AN SEVIN
}}
The Sevin Process
• Toxic, flammable gas• Boiling point is near to
ambient• Runaway reaction with
water possible unless chilled below 11 C
M I C Hazards
NFPA Diamond
Flammability
Toxicity Reactivity
DOT = US Dept of Transport
CAS = Chemical Abstracts No.
ID = United Nations Ref No.
Properties of MIC
Reaction SystemReaction System
Phosgene StillPhosgene Still
PyrolysisPyrolysis
MIC Refining StillMIC Refining Still
MIC StorageMIC Storage
MMA Phosgene
HCl
Chloroform
TailsResidue
Flare and Scrubber Derivatives Plant
Simplified Process Flow Chart
SAFEGUARD TYPE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Mounded/insulated MIC Tanks
Refrigeration below reaction initiation temperature
Refrigeration uses non-aqueous refrigerant (Freon)
Corrosion protection (cathodic) to prevent water ingress
Rigorous water isolation procedures (slip blinds)
Nitrogen padding gas used for MIC transfer not pumped
Relief Valve and rupture disk
Vent gas scrubber with continuous caustic circulation
Elevated flare
Water Curtain around MIC Tanks
Passive
Active
Active
Active
Active
Active
Passive
Active
Passive + Active
Active
MIC Safeguards Table
1. Why it was not categorized as passive? It is permanently installed
2. What would you say constitutes a passive safeguard ?
The vent gas scrubber was defined previously as an active safeguard
What do we mean by Safeguards?
Accidents are normally characterised by a sequence of events leading from the initiating event, propagation of the accident, and realisation of the undesired outcome
Safeguards may be equipment items or procedures designed to prevent the initiating event, limit or terminate the propagation, or mitigate the outcome
Active safeguards are those which require human procedures or mechanical initiation to operate (e.g. work permit procedures, scrubber caustic circulation)
Safeguards
Passive safeguards are those which are designed in and which do not require any initiation (e.g. concrete fireproofing, elevated vent stack for dispersion)
Both active and passive safeguards can be defeated through inadequate Safety Management Systems
Safeguards
A-Napthol plant shut down SEVIN production no longer making
money, so cost savings sought, and plant run intermittently
Minimum maintenance Safety procedures simplified for small
jobs Refrigeration unit shut down and Freon
sold Scrubber circulation stopped Manning cut to 600 Morale low Slip blinding no longer mandatory
during washing High temperature alarm shut-off as
T now > 11 C
RV and PCV headers joined (for maintenance)
Emergency flare line corroded, disconnected
1981-1984: 6 accidents with phosgene or MIC
1982 audit critical of MIC tank and instrumentation
1984 warning of potential runaway reaction hazard
Plant Problems – Precursor to Disaster
Occurred late at night, soon after shift changeMIC tank overheated, over-pressured and vented
through scrubberElevated discharge of massive quantity of MIC
(approximately 25 tons)Operational staff retreated upwind, no casualtiesStaff from other plants evacuated, few casualties
The Incident
Source of WaterFilters were being flushed using high pressure
waterDrain line from filter was blocked, operator
observed no flow to drainFlushing continued despite blockageHigh pressure could cause valve leak; force
water into relief header and then?
Incident Causes
Route of WaterRV and PCV headers were joined by jumper pipe,
no blindsMIC tank could not be pressurised because tank
PCV failed open?Leakage through a single valve would allow water
from RV header to enter tankHead of water sufficient for flowSlow initial reaction would allow 1600 lbs. to enter
Incident Causes
Water Drain
PI
RV
Valve which let water in
Quench Filter - pressuresafety valve lines(at ground level)
Phosphene Stripping -Still Filter- pressuresafety valve lines(at ground level)
To VCS RWH Line
To VGS and FVH FVH Line
N2 Header Isolation Valve
RuptureDisk
Concrete Cover
From MRS
From Refrigeration
To Reactor Conditioner
Refrigerator
Tank No. 610
40 PSI
Educator
MRS MIC Reactor SideRVVH Relief Valve Vent HeaderPVH Process Valve Vent HeaderVGS Vent Gas ScrubberFVH Flare Vent Header
Route of water ingress
ToVCS
PI
JumperLine
Slip Blindrequired here
WaterSourceArea
Ultimate destination of water
Probable Route of Ingress of Water into Tank 610
Water Drain
PI
RV
Valve which let water in
Quench Filter - pressuresafety valve lines(at ground level)
Phosphene Stripping -Still Filter- pressuresafety valve lines(at ground level)
To VCS RWH Line
To VGS and FVH FVH Line
N2 Header Isolation Valve
RuptureDisk
Concrete Cover
From MRS
From Refrigeration
To Reactor Conditioner
Refrigerator
Tank No. 610
Educator
MRS MIC Reactor SideRVVH Relief Valve Vent HeaderPVH Process Valve Vent HeaderVGS Vent Gas ScrubberFVH Flare Vent Header
Route of gas leakage after 0030
ToVCS
PI
40 PSI
JumperLine
MICto
vent
Ventnot
working!
Reaction
Probable Route of Gas Leakage before 0030 hrs
Water Drain
PI
RV
Valve which let water in
Quench Filter - pressuresafety valve lines(at ground level)
Phosphene Stripping -Still Filter- pressuresafety valve lines(at ground level)
To VCS RWH Line
To VGS and FVH FVH Line
N2 Header Isolation Valve
RuptureDisk
Concrete Cover
From MRS
From Refrigeration
To Reactor Conditioner
Refrigerator
Tank No. 610
Educator
MRS MIC Reactor SideRVVH Relief Valve Vent HeaderPVH Process Valve Vent HeaderVGS Vent Gas ScrubberFVH Flare Vent Header
Route of gas leakage before 0030
ToVCS
PI
40 PSI
JumperLine
Rupture disk bursts
Increased rate of release
Probable Route of Gas Leakage after 0030 hrs
No alarm or warning to publicVery stable atmosphere and low wind
directly into townSurrounding population asleepOver 2,500 fatalitiesOver 250,000 sought medical treatmentPanic
The Incident
Note how the cloud boundary (to the level of “serious” harm) almost exactly matches the area of highest population density
Had the wind blown north the Bhopal incident, although it would have still been serious, would have been less disastrous
Other incidents could have been worse but for luck in timing and the wind directionSeveso (wind direction)Flixborough (occurred at a week-
end)
The Incident’s Extent
Chemistry causing incident is not in dispute
41 tonnes of MIC in storage reacted with 500 to 900 kg water plus contaminants
Resultant exothermic reaction reached 400 to 480ºF(200 to 250ºC)
Tank pressure rose to 200+ psig (14+ bar) - tank was designed for 70 psig (4 bar)
Venting caused ground to shake!
Incident Chemistry
No universally accepted cause.Sabotage theory
Disgruntled employeeAlternative theory involves connection of water
hose to storage tank 610Evidence said to include the finding of the
disconnected pressure gauge from tank 610 after the disaster
A rough drawing found, said to depict a hose connected to a pressure vessel
Management systems theory Inadequate safety management allowed water
entry through inadequate slip-blinding and uncontrolled plant modifications
Design safeguards should have prevented the disaster of either case
ZZ
ZZ
Z
OR ?
Incident Causes
Many theories can be put forward and all mechanisms give insights into the vulnerability of the system
Main objective is to learn from the consequences; multiple possible causes only serve to highlight the weaknesses
Incident Causes
Early safety study would question hazardous inventories and plant siting
Detailed study would identify contamination problem
Safety Studies may propose a training function, should involve parent company staff
Safety Studies may review procedures, especially those involving hazards (water washing?)
Lessons
Learnt
What Could Safety Studies have done?