Hazards in Process Industries

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Hazards in Process Industries

• DR. AA

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Hazards 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

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Toxic Substances
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Hazard 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 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

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Classification of Chemical Hazardous to Health

• Very Toxic
• Toxic
• Corrosive
• Harmful
• Irritant
• Sensitizer

• Carcinogenic
• Category 1,2,3
• Mutagenic
• Category 1,2,3
• Teratogenic
• Category 1,2

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

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2. Fire

• Jet Fire
• Flash Fire
• Pool Fire

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Flash 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.

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Jet Fire
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Pool Fire
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Explosion
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Classification of Explosions
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Types of Explosion

• Vapour Cloud Explosion
• Confined
• Unconfined
• BLEVE
• Mechanical Explosion
• Chemical Explosion

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Distance of Effect Comparison
INVENTORY (tons)
BLEVE
UVCE
FIRE
Distancein Meters
1 2 5 10 20 50 100 200 500 1000
18 36 60 90 130 200 280 400 600 820
120 150 200 250 310 420 530 670 900 1150
20 30 36 50 60 100 130
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Physical Explosion

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

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Chemical 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 gtgt10 bars

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Vapor 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.

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Factors Favoring Overpressures of Vapor Cloud

• 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.
• Cloud composition
• Highly unsaturated molecules are bad due to high
  flammable range, low ignition energy, high flame
  speed etc.
• Weather
• Stable atmospheres lead to large clouds.
• Low wind speed encourages large clouds.

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Factors Favoring Overpressures of Vapor Cloud

• Vapor Cloud Size impacts on
• probability of finding ignition source
• likelihood of generating any overpressure
• magnitude of overpressure
• 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

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Impact of VCEs on People
PeakOverpressure psi
EquivalentWind Velocity mph
Effects
70 160 290 470 670 940
Knock personnel down Rupture eardrums Damage
lungs Threshold fatalities 50 fatalities 99
fatalities
1 2 5 10 15 20 30 35 50 65
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Impact of VCEs on Facilities
PeakOverpressure psi
Typical Damage
Glass windows break Common siding types
fail - corrugated asbestos shatters -
corrugated steel panel joints fail - wood siding
blows in Unreinforced concrete, cinder block
walls fail Self-framed steel panel buildings
collapse Oil storage tanks rupture Utility poles
snap Loaded rail cars overturn Unreinforced brick
walls fail
0.5-to-1 1-to-2 2-to-3 3-to-4 5 7 7-8
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Damage 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

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Phillips Pasadena, USA

• 23rd Oct. 1989
• 23 Deaths 130 Injuries
• Vapour Cloud explosion
• Loss US 500 Millions

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

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Mechanism 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.

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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

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The Tragedy Of San Juanico, PEMEX, 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.
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Pemex Before BLEVE
Plot Plan
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Plot Plan - After
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Initiating 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.

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Initiating Event Contd

• 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.

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Failure
Spherical Tank Failure (F4)
Bullet Tank Area
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Impact
Cylindrical tank flew as missiles
Nearby Houses

• 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.

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Emergency 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.

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Lessons 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.