Safety Case Studies Flashcards
Admin Barriers Case Study
Formosa - vinyl chloride release
April 23rd 2004
Plant used to produce PVC constructed in 1996, Formosa purchased in 02
Initial Causes:
Worker opened valve on pressurised reactor of flammable vinyl chloride – was cleaning reactor # from the top level and went to bottom floor reactor 310 instead with the intention of releasing cleaning water. Valve wouldn’t open so used emergency air override hose. PVC spilled everywhere. No large release emergency drill in 10 years. In 99, bottom valve interlock was deemed suitable
Consequences:
2 operators did not evacuate and died, 5 died total, 3 injured
Facility destroyed and fire lasted 2 days
Acrid smoke into the community
150 residents evacuated
Lessons Learnt:
• Engineering safety offices in bad location
• Not adequate evacuation training
• Reactors grouped too similarly
• No indicators on lower level of reactor on
• Control panel split top and ground floor – no radios for communication
• Interlock on bottom reactor valve susceptible to misuse
• Make appropriate changes based on past experiences – in 2003, Formosa Baton Rouge opened wrong reactor spilling 8000 pounds vinyl chloride to atmosphere – similar accident in 2004
Suggested steps:
• Review design and operation of reactors
• Design chemical processes to minimise consequences of human error
• Improve control safety interlocks
• More thoroughly evaluate high risk hazards
• Consider all consequences in near miss investigations
• Improve emergency evacuation drills
Barrier Vulnerability Case Study
Piper Alpha - gas release from unsecured flange after condensate pump switch
Dispersion Case Study
T2 Laboratories - MCMT reactor thermal runaway
Reactive chemistry hazards unknown
Cooling water system inappropriate
Rupture disk set at 400psi
Toxic Release Case Study
Bhopal (minimal)
MGPI - Sulfuric Acid and Sodium Hypochlorite accidentally mixed - toxic chlorine vapour cloud
Dust Flash Fire Case Study
Hoeaganaes
- Bucket elevator motor fix sent dust into the air and ignited
- Furnace fix using hammer propagated dust which then ignited
- Hydrogen leak from underground piping after hot water corrosion. Spark generated from forklift caused explosion
Vapour Cloud Explosion Case Study
Buncefield - overflow of gasoline tank formed vapour cloud which ignited and caused 20 others to explode
Dust Explosion Case Study
Imperial Sugar - steel covers on belt conveyors allowed dangerous levels of dust to accumulate. Most likely exploded due to overheated bearing. Caused further dust to be propagated leading to more explosions
Non-conductive Flammable Liquid Explosion Case Study
Barton Solvents - ignitable vapour-air mix in 15,000 V&MP Naptha non-conductive flammable solvent tank. Rapid charge accumulation from stop-start filling. Liquid level gauge float broke grounding circuit leading to an explosion
Inherent Safety Case Study
Bhopal - better methods could have been used
Management of Change Case Study
Flixborough - caprolactam factory used dog-leg bridge to connect reactors. Failed leading to release of 40 tons of cyclohexane vapour. Ignited causing explosion
Williams Olefins - heat exchanger rupture - completely isolated from pressure relief valve
Permit to Work Case Study
Valero Delaware - two workers died in the top of a reactor due to nitrogen asphyxiation
Loss of containment initiating causes
Over pressure, maintenance error, external energy, gradual failure, accidental release (OMEGA)
Factors determining severity of containment loss
Time, inventory, materials, energy, exposure
Barriers
Passive, active, admin
Hazard
Source of potential damage
Risk
Probability of harm to person or process if exposed to a hazard
What If? Analysis
What if? Hazard/consequences? Safeguards? Recommendations?
HAZOP vs HAZID
HAZOP for one unit op HAZID for the whole plant
Fault Tree Analysis
From top event (high consequence) to root causes
Event Tree Analysis
All possible outcomes of an event taking into account whether installed barriers did or didn’t work
Accidental event/additional event occurs/barrier 1 does not function/ barrier 2 does not function/outcome and consequence
Flammable
Flash point below 37C
Combustible
Flash point above 37C
Factors affecting dispersion
Release velocity, buoyancy, amount/duration, temperature, weather, terrain
Discharge vs dispersion
High to atm pressure vs atm pressure spread
