Hazard Identification

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Hazard Identification
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The Most Common Chemical Plant Accidents is
Fire, Explosion, Toxic Release

• To prevent these accidents, engineers need to
  familiar with
• Fire, explosion and toxicity properties of
  materials
• Nature of fire, explosion and toxic release
  process
• Procedures to reduce fire, explosion and toxic
  release hazards

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Fires

• Pool Fire
• Liquid spilled onto the ground spreads out to
  form a pool.
• Volatile liquid (e.g. petrol) evaporate to
  atmosphere and soon form flammable mixture with
  air.
• Upon ignition, a fire will burn over the pool.
• The heat vaporizes more petrol and air is drawn
  in round to the side to support combustion.
• Danger to people is by direct thermal radiation
  and burn.

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• Flash Fire
• If spilled material relatively volatile (e.g.
  propane, butane, LPG) it would still form a pool
  but evaporation would be much more rapid.
• If ignition did not take place immediately to
  form pool fire, then sizeable vapor cloud
  would form, drifted away by wind, to form cloud
  within flammable range.
• If found source of ignition, flash fire will
  occur. People at risk from thermal radiation
  effects.
• Usually unexpected event and short duration

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• Torch Fire
• High pressure release of gas from a vessel or
  pipeline ignites almost immediately.
• This give rises to a giant burner of flame
  length tens of meters.
• Danger from thermal radiation and also
  impingement on adjacent pressurized vessel,
  such as LPG vessel, heating the content followed
  by pressure build up causing boiling liquid
  expanding vapor explosion (BLEVE).

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Distinction between Fires and Explosions

• Major difference between fires and explosions is
  the rate of energy release. Fires release energy
  slowly, while explosions release energy very
  rapidly (eg automobile tire explosion).
• For explosion to occurs,
• Explosive mixtures
• Initiation of reaction (ignition or detonation)
• Rapidity of reaction
• Rapid liberation of heat causes gas to expand and
  high pressure build up
• Rapid expansion of gases to rapidly generate high
  pressure
• .Explosion!!!!!!!
• Note Rubber tire explosion and vessel rupture
  due to overpressure are examples of mechanical
  explosion, i.e. no explosive mixture involve.

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• BLEVE (Boiling Liquid Expanding Vapor Explosion)
• Flammable materials stored under pressure at
  ambient temp, e.g LPG or ethylene oxide bullet
  tank. Fire could start from external spillage or
  leak and the flames impinge on the side of the
  vessel.
• The metal of the heated vessel at high
  temperature becomes weak and finally ruptures
  allow the content to rapidly escape forming
  large vapor cloud and entrained liquid.
• Cloud then ignited by original fire. Casualty
  from blast effect is due to thermal radiation or
  missiles.

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Examples a) Feyzin, France, 4/1/66. A
leak on propane storage sphere ignited and caused
fire which burned fiercely around the vessel and
led to BLEVE. 18 death, 81 injuries. b)
Mexico City, Mexico, 19/11/84. A series of LPG
explosions at LPG gas distribution plant
resulted in 542 killed and over 7000 injured. LPG
was stored in 6 spheres and 48 cylindrical
bullets holding 4 million gallons of LPG.
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Video on Bleve Explosion
http//www.youtube.com/watch?vGWjxrAhpBQk http/
/www.youtube.com/watch?vwcmmLvAYqkI
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• 2. UVCE (Unconfined Vapor Cloud Explosion)
• An explosion occuring in the open air which
  results from the ignition of flammable gas. An
  unconfined vapor-cloud explosion may result from
  the accidental release of a flammable liquid or
  gas.
• Example
• Flixborough, UK, 1/6/74. Plant producing
  caprolactam for nylon manufacture and part of the
  process involved reaction of cyclohexane with
  air. Massive failure of a temporary bypass
  pipeline cause 40 -50 ton of liquid cyclohexane
  to escape and formed a large vapor cloud.
  Subsequent explosion cause damage up to 3 miles
  away. 28 killed, 36 injured on site, 53 off-site.

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UVCE
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UVCE and Pool Fire
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• 3. Confined Vapor Explosion
• Explosion in a vessel or building
• Vapor cloud drifts/leaks into a building and
  ignites, the resulting fire raises temperature
  and increases pressure by a factor of 8 to
  10.sufficient to collapse wall or roof.
• Example Abbeystead disaster - Build up methane
  gas from earth within tunnels in water pumping
  station ignited, killing several of visitors.
• 4. Dust Explosions
• Inherent hazard whenever combustible solids of
  small particle size are handled. Eg Coal, flour,
  wood dust, resin dust
• Example Series of explosions in silos at New
  Orleans in 1977. 45 silos containing corn, wheat
  and soy beans involved35 to 50 people killed.

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Damage by wood dust explosion
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Damage by resin dust explosion
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Toxic Release

• Toxic chemicals can cause harm by inhalation,
  skin absorption, or ingestion.
• Short term and also long term effect from
  inhalation, absorption and ingestion as well as
  identification, evaluation and control of
  toxicants are covered under chapter Toxicity and
  Industrial Hygiene.
• Example
• a) Seveso, Italy, 10/7/76. Release of material
  containing dioxin to atmosphere. Incident after
  a series of not following specified procedure.
  About 2 kg of dioxin was discharge through relief
  valve to atmosphere. Heavy rain washed toxic
  chemical, absorbed into soil. 600 people
  evacuated, 2000 given blood test and many people
  suffered from skin disease

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1. Manfredonia, Italy, 26/9/76. Aerosol mixture
   containing 10 tons of K3AsO3 and H3AsO3 escaped
   from NH3 cooling column. Explosion resulted in 60
   tons of water, 10 tons of arsenic trioxide and 18
   tons of potassium oxide released into atmosphere.
   Contaminated 15 km2 of cultivated land from 2 km2
   area around the plant with arsenic. Fishing
   prohibited and 30 people contaminated. Area
   declared safe in Jan 1977.
2. Bhopal, India, 3/12/85. Runaway reaction caused
   release of methyl isocynate (MIC) and possibly
   hydrogen cyanide. 2500 fatalities and 200,000
   injuries. Identified causes Inadequate design
   pipe work, inadequate procedures, inadequate
   emergency plan, inadequate job supervision,
   inadequate maintenance of protective equipment,
   inadequate management capabilities, and possibly
   sabotage.

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Hazard Identification

• Hazard Survey/Hazard Inventory - Identifies all
  stocks of hazardous material with details of
  conditions of storage and information on nature
  of hazard i.e toxic, flammable etc (conceptual
  design stage).
• Hazard Indices - Checklist method of hazard
  identification which provides a comparative
  ranking of the degree of hazard posed by a
  particular design conditions, i.e the Mond Index
  and the Dow Fire and Explosion Index (detailed
  design stage).
• Hazard and Operability Study (HAZOP) - A formal
  systematic method of identifying hazards and
  operability problems by used of guide words
  (detailed design stage).
• Failure Mode and Effects Analysis (FMEA) - Hazard
  identification method where all known failure
  modes of components or features of a system are
  considered in turn and undesired outcomes noted.
  If the chances of failures and the seriousness of
  the consequences are ranked to identify the most
  critical features it becomes Failure modes,
  Effects and Criticality Analysis (FMECA)
  (detailed design stage).