Hazards in Process Hazards in Process IndustriesIndustries

DR. AA

Hazards in Process IndustriesHazards in Process Industries

• There are Three Major Hazards: Toxic Release, Fire, Explosion

• Toxic Release– Impacts of people and environment. e.g. Bhopal

• Fire – Impacts on plant, people and environment– May also followed by toxic release

• Explosion– Same as fire but more severe

Toxic Toxic SubstancesSubstances

Hazard from Toxic SubstancesHazard from Toxic Substances• There are no harmless substance, only

harmless ways of using substances• Toxicants

– A chemical agents– A physical (dusts, fibers, noise, and radiation)

agents, e.g. asbestos– Toxicity is a property of toxicant that describe its

effect on biological organism.– Toxic hazards is the likelihood of damage to

biological organism based on exposure resulting from the use/transport/storage of the toxicants (hazardous material).

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Hazard from Toxic SubstancesHazard from Toxic Substances

• Source of Toxicants– Toxic Release– Fire and Explosion

• Route of Entry – Injection: through cuts or hypodermic needles into the skin,

usually cause highest blood level concentration.– Inhalation: through mouth/nose into the lungs– Ingestion: through mouth into stomach and gastrointestinal

tract, – Dermal (Skin) absorption: through skin membrane

Classification of Chemical Hazardous to Classification of Chemical Hazardous to Health Health

Very Toxic Toxic Corrosive Harmful Irritant Sensitizer

Carcinogenic– Category 1,2,3

Mutagenic– Category 1,2,3

Teratogenic– Category 1,2

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Data on toxicity can be found on Chemical Safety Data Sheet (CSDS)

Hazard from Toxic SubstancesHazard from Toxic Substances

• Effects that are Irreversible– Carcinogen-cause cancer– Mutagen-cause chromosome (gene) damage– Teratogen- cause birth defects

• Effects that may or may not be irreversible– Dermatotoxic – affects skin– Hemotoxic – affects blood– Hepatotoxic- affects liver– Nephrotoxic – affects kidneys– Neutotoxic – affects nervous system– Pulmonotoxic- affects lungs

2. Fire2. Fire

• Jet Fire• Flash Fire• Pool Fire

Flash FireFlash Fire

• Flash fire is the non explosive combustion of a vapour cloud resulting from a release of flammable material into the open air, which, after mixing with air, ignites.

• Combustion in a vapour cloud develops an explosive intensity and attendant blast effects only in areas where intensity turbulent combustion develops and only if certain conditions are met.

• Where these condition are not present, no blast should occur.

• The cloud than burns as a flash fire, and its major hazard is from the effect of heat from thermal radiation.

Jet FireJet Fire

Pool FirePool Fire

ExplosionExplosion

Classification of ExplosionsClassification of Explosions

EXPLOSION =Rapid Equilibration of High Pressure Gas via Shock Wave

Physical Explosions Chemical Explosions

Propagating ReactionsUniform Reactions

Thermal Explosions Deflagrations(Normal Transport)

Detonations(Shock Wave)

Types of ExplosionTypes of Explosion

• Vapour Cloud Explosion– Confined– Unconfined

• BLEVE• Mechanical Explosion• Chemical Explosion

Distance of Effect ComparisonDistance of Effect Comparison

125

102050

100200500

1000

INVENTORY(tons)

18366090

130200280400600820

BLEVE

120150200250310420530670900

1150

UVCE

2030365060

100130

FIRE

Distancein Meters

Physical ExplosionPhysical Explosion

• Explosion due to overpressure of materials stored in a container.

Chemical ExplosionChemical Explosion

• Deflagration– Combustion with flame speeds at non turbulent velocities of 0.5 - 1 m/sec.

– Pressures rise by heat balance in fixed volume with pressure ratio of about 10.

• Detonation– Highly turbulent combustion– Very high flame speeds– Extremely high pressures >>10 bars

Vapor Cloud ExplosionVapor Cloud Explosion

• Cloud will spread from too rich, through flammable range to too lean.

• Edges start to burn through deflagration (steady state combustion).

• Cloud will disperse through natural convection.

• Flame velocity will increase with containment and turbulence.

• If velocity is high enough cloud will detonate.

• If cloud is small enough with little confinement it cannot explode.

Factors Favoring Overpressures of Vapor CloudFactors Favoring Overpressures of Vapor Cloud

1. Confinement– Prevents combustion products escaping, giving higher local

pressures even with deflagration.

– Creates turbulence, a precursor for detonation.

– Terrain can cause confinement.

– Onsite leaks have a much higher potential for UVCE than offset leaks.

2. Cloud composition– Highly unsaturated molecules are bad due to high flammable

range, low ignition energy, high flame speed etc.

3. Weather

– Stable atmospheres lead to large clouds.

– Low wind speed encourages large clouds.

4. Vapor Cloud Size impacts on:

– probability of finding ignition source

– likelihood of generating any overpressure

– magnitude of overpressure

5. Source

– flashing liquids seem to give high overpressure

– vapor systems need very large failures to cause UVCE

– slow leaks give time for cloud to disperse naturally without finding an ignition source

– high pressure gives premixing required for large combustion

– equipment failures where leak is not vertically upwards increases likelihood of large cloud

Factors Favoring Overpressures of Vapor CloudFactors Favoring Overpressures of Vapor Cloud

70160290

470670

940

12 5

10 1520 30 355065

PeakOverpressure

psi

EquivalentWind Velocity

mph

Knock personnel down

Rupture eardrums

Damage lungs

Threshold fatalities50% fatalities99% fatalities

Effects

Impact of VCEs on PeopleImpact of VCEs on People

0.5-to-11-to-2

2-to-33-to-4

57

7-8

PeakOverpressure

psi

Glass windows breakCommon siding types fail:

- corrugated asbestos shatters- corrugated steel panel joints fail- wood siding blows in

Unreinforced concrete, cinder block walls failSelf-framed steel panel buildings collapseOil storage tanks ruptureUtility poles snapLoaded rail cars overturnUnreinforced brick walls fail

Typical Damage

Impact of VCEs on FacilitiesImpact of VCEs on Facilities

Damage from Vapor Cloud ExplosionsDamage from Vapor Cloud Explosions

Peak Overpressure Typical Damage (psi)

3 - 4 Self-framed steel panel buildings collapse.

Oil storage tanks rupture.

5 Utility poles snap

7 Loaded rail cars overturn

7 - 8 Unreinforced brick walls fail

Phillips Pasadena, USAPhillips Pasadena, USA

• 23rd Oct. 1989

• 23 Deaths 130 Injuries

• Vapour Cloud explosion

• Loss US$ 500 Millions

BLEVEBLEVE

B L E VOILING

IQUID

XPANDING

XPLOSIONS

EAPOR

BLEVE is a consequence of holding a pressurized flammable liquids above its boiling point.

Causes of BLEVECauses of BLEVE

• The immediate cause of the BLEVE is rupture of the container. If the pressure inside the vessel exceeds the outside strength of the walls the vessel will fail.

• If the vessel is overfilled and expansion (due to boiling of liquid) results in a heavy hydrostatic pressure.

• If the vessel is weakened by mechanical damage or by high temperature resulting from immersion in a fire then failure can occur.

Mechanism of BLEVEMechanism of BLEVE

• When BLEVE is initiated, the liquid boils off rapidly producing a reaction which turns parts of the ruptured vessel into rockets which can travel 2500 ft or more.

• The liquid can take fire if it is flammable and burning material can spread over a large area. If the gas or liquid mixes with air a vapour cloud explosion can occur.

FEYZIN, 04.01.1966, FRANCE• 4TH JAN. 1966 FRANCE

• 18 KILLED, 81 INJURED

• LEAK IN 1200 M3 PROPANE SPHERE LEADING TO BLEVE

• FURTHER SPHERE TOPPLED

• ADJACENT PETROL TANK CAUGHT FIRE

• 48 HRS TO GAIN CONTROL

The Tragedy Of San Juanico, The Tragedy Of San Juanico, PEMEX, Mexico City, 19 Nov 84PEMEX, Mexico City, 19 Nov 84

• Pemex is a liquid petroleum gas ( LPG) distribution plant.

• Pemex is located a few km. north of Mexico City (Pop = 16MM).

• Plant was 25 years old and built to 1950 API standards of the U.S.

• LPG gas is used for heating and cooking in almost every household.

15 of 48 Vessels BLEVE In Domino Fashion 550 people killed.2,000 people receive severe burns.7,231 people classed as injured.

Pemex – Before BLEVEPemex – Before BLEVE

Plot Plan

Plot Plan - AfterPlot Plan - After

Initiating EventInitiating Event• EBV shuts feed to a sphere at 90% full.

• Possible “water hammer” damages the 8 in. feed pipe near the vapor phase of F-4.

• Vapor cloud drifts toward a ground flare, ignites and causes a flash fire.

• The flame burns back to source and impinges on vapor space of sphere F-4.

• 10 minutes after line rupture, sphere F-4 BLEVEs.

• Vessel explosion as pressure is relieved.

• Fire ball from flashing contents.

• Large energy release breaks vessel into pieces which fly off as missiles.

Initiating Event Cont’dInitiating Event Cont’d

• Missiles from F-4 strike other vessels.• More liquid leaks, more fires and other BLEVEs

are created.• 14 other vessels BLEVE in domino fashion

over a 5 hour period.• The site emergency fire water system is

overwhelmed.

FailureFailure

Bullet Tank Area

Spherical Tank Failure (F4)

ImpactImpact

Nearby Houses

Cylindrical tank flew as missiles

• F1, F2, F3 and F4 spheres disappear.

• Avg. wt. of a bullet vessel was 20 tons.

• Furthest missile traveled 1,200 meters.

• Burning HCs rained on neighboring village 130m from fence line.

Emergency ResponseEmergency Response

• First firefighters arrive 15 minutes after F-4 BLEVE.

• 100 ambulances and 200 firefighters involved.• 985 medics and 1,780 paramedics involved.• 1,332 medical volunteers in 33 hospitals

involved.

Lessons LearnedLessons Learned

• Old plant, too congested, poor maintenance & poor operator training were cited.

• Village should have been 1,500 meters from terminal (determined by QRA analysis).

• Require many gas detectors and alarms.• EBV closure rates need adjustment.• Emergency plan required.