Transcript Hazard Identification - HAZOP Malaysia | Process Safety

Hazard
Identification
The Most Common
Chemical Plant Accidents is Fire,
Explosion, Toxic Release
To prevent these accidents, engineers need to familiar with:
(1) Fire, explosion and toxicity properties of materials
(2) Nature of fire, explosion and toxic release process
(3) Procedures to reduce fire, explosion and toxic release
hazards
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Fires
1.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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2. Flash Fire
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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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3.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,
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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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1. 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?v=GWjxrAhpBQk
http://www.youtube.com/watch?v=wcmmLvAYqkI
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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 involved…35 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
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Toxic chemicals can cause harm by inhalation, skin absorption, or
ingestion.
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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.
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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
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b) 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.
c) 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
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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).
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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).
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Hazard and Operability Study (HAZOP) - A formal systematic method of
identifying hazards and operability problems by used of guide words (detailed
design stage).
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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).
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