Safety Alerts 19

Petrochemicals

• C3=: Poor vapor freeing: Reactor with C3= and a layer polypropylene granules was purged with Nitrogen six times. But it released C3= held among the granules when filled with water. WWW

• C4: Liquid phase oxidation of Butane. Insufficient purging of reactor when it was down resulted in an explosion releasing reactor’s contents. VCE

• EO: Ammonia leaked past several check valves + positive displacement pump RV into Ethylene Oxide tank. Tank ruptured and EO cloud exploded

• EO: Cycle fatigues resulted in a hairline crack in the welded seam of Level Indicator (LI) on Aldehyde Column. Minor EO leak that formed PEG that accumulated in the mineral wool insulation. During repairs to LI, on removing insulation metal sheath, air contacted the insulation soaked with PEG. Auto-oxidation and ignition heating the LI piping. Decomposition of EO within the piping propagated to the column that then exploded

• EO: Explosion in final purification column of EO plant. Decomposition of contents led to rapid over-pressurization

• PO: Wastewater tank storing Propylene Oxide and Styrene plant wastes. N2 Blanket Compressor was under maintenance. Tank O2 level was monitored by a temporary O2 analyzer to purge with N2, if required. Peroxides and Caustic in waste. O2 build up from peroxides decomposition was not detected by the O2 analyzer in a dead zone. On restart, the tank Off Gas Compressor sucked in flammable vapor that was ignited and flashed back to the tank. Tank exploded killing 17. Ignorance of peroxide presence and its decomposition + poor location of O2 analyzer + stopped N2 purging. AIChE CEP

• Styrene plant: During Benzene unit restart, a flange gasket burst releasing H2. Explosion. Instead of spiral-wound gasket, only compressed asbestos fiber (CAF) gaskets were in use

• Improper and prolonged storage of hazardous chemicals can result in large explosions

• See Reactor Relief Sizing Mistakes, under Relief

• EO: Reactor making MPEG 500 (Polyethylene Glycol Methyl Ether) from EO and Methanol exploded. Likely causes - insufficient catalyst resulting in unreacted EO leading to a runway reaction followed by an internal gas phase explosion. Rupture disk was sized for fire only

• PVC: 24 identical reactors. While trying to empty wash water from an isolated reactor, operator forced open drain valve of another reactor in service. Flammable VC release and explosion. Interlock override by mistake without cross checking + poor or no communication + no running status display near the valve

• PVC: Mechanic removed top manhole cover of an autoclave and went down to the floor below to remove manhole at bottom. By mistake opened the manhole of the adjoining autoclave. Vinyl Chloride and Nitrogen at pressure blew off the cover. 3 fatalities. WWW

• Acrylic Acid: Intermediate tank provided between 2 columns purifying AA. Feed to downstream column was stopped for test runs. AA accumulated in the tank. Cooling coils at tank bottom was not effective to cool accumulating layers. Dimerization heat led to polymerization. Tank exploded and fire

• Acrylic Polymerization: Batch process. Monomer + solvent added in steps, heated with steam in jacket to a specified temperature. Then heating was switched off and initiator added. Hot solvent vapor from heat of reaction cooled in overhead condenser and sent to the reactor to keep it cool and then further monomer/ initiator added over an extended period. When the full batch was added in one go, heat output was high. Flammable vapor and explosion

• Acrylic polymer: 12 % more than normal batch. All the monomers were added. Next, the solvents (Toluene and Cyclohexane) and the initiator were added. Then part of the extra 12% more monomer was added - though the additional monomer for the larger batch was in the initial charge. Then the contents were heated and the initiator solution was added. Due to runaway reaction vapor vented from the reactor manway, forcing the operators out of the building. Building then exploded. Inadequate cooling. Fouled condenser that was not inspected or cleaned of sediment, scale and rust in its 30 years of service

• Butadiene: Known to form Popcorn Polymer that blocked RV inlet and HX. Slope RV inlet to avoid liquid accumulation. Piping/ equipment rupture on rapid growth/ expansion. Unstable Pyrophoric Polymers and explosive Polyperoxides. Many incidents. Minimize air ingress. Inhibit. Popcorn accumulation and expansion in dead-legs led to line rupture, Butadiene release, explosion and fire. Identify and eliminate dead-legs

• MTBE: Temporary suction hose used to empty a reactor. Hose incompatible with the pumped fluid. On improper discharge throttling the pump, the hose ruptured. Ignition. VCE. BLEVE. Contributing factors - failure to maintain a LIC, FCV and RV

• Mononitrotoluene: Produced by reacting Toluene with nitrating acid. The resulting MNT, residual acid, Toluene, and water were separated, spent acid concentrated and recycled. Toluene stripper removed residual Toluene. MNT liquid was separated in a 3 column distillation unit into ortho-, meta-, and para-MNT. The column operated under vacuum. The plant was shut down following a series of incidents including a fire in a Hydrogen unit and loss of vacuum in the distillation unit with MNT. After a month, the plant was restarted and column bottom temperature steadily increased. Vapor generated accumulated on the chimney tray at column top, resulting in a tray LAH. The column ruptured and its top was blown away. Column wall fragments hit a storage tank. Fire. Unit cooling tower was struck by debris and caught fire. Reboiler leaking steam valves had cooked MNT in column top, releasing gases and pressurizing the column. No TAH/ PAH

• Runaway Reaction: Reactor MAWP 5.3 bar at 180°C. A rupture disc + Relief valve set at 5.3 bar. Automatic vent valve to control pressure. Temperature controlled by either steam or cooling water in wall mounted coils. An agitator mixed the contents. Reaction at 0.85 bar and 149°C. While on steam heating, pressure and temperature shot up. Vent valve failed to open. Operators switched to Cooling Water. Runaway reaction. Vessel ruptured and blown away at 16.7 bar and 179°C. CSB

• Runaway Reaction: Steps - Add PNO, then Acetone as a ‘heat sink’ for the exothermic reaction of PNO and DECC, and then add DECC. Acetone was not added. Runaway exothermic reaction blew the reactor top, though there were 2 independent relief paths - RD + RV and RD. Interlock feed valves ?

• Runaway Reaction: Agitator failure led to poor mixing in an exothermic reactor. Chemical continued to be added. On starting the agitator, unreacted chemicals reacted, led to higher temperature which the cooler was unable to handle. Chemicals vented via relief valve impacting nearby residents

• Runaway Reaction: During a weekend, plant was shut down, reactants left at 158°C, below runaway reaction temperature of 230°C. Reactor contents not stirred or heated or cooled. Due to reduced weekend site load, turbine exhaust steam temperature rose to ~ 300°C (Normal 190°C), heated the reactor wall above the reactants to 300°C, radiating heat to the unstirred and uncooled reactants heating the top crust to 180 - 190°C. Exothermic slow reaction at 180°C for over 7 hours. RD ruptured discharging toxic dioxin. Lessons learnt: (1) Limit heating media temperature (2) Relief should exhaust to containment systems (3) Three similar past incidents where hot oil at 300°C was used and the manual heating control failed

• Runaway Reaction: On rising temperature, the batch was overcooled leading to unreacted components accumulation. Resultant runaway reaction blew and propelled off the reactor. Overcooling can damage too

• Runaway Reaction: Triallyl Cyanurate. First batch of a new product. Runaway reaction released flammable and toxic Allyl Alcohol and Allyl Chloride via manway seal and rupture disk. Undersized cooler, inadequate vent disposal, poor hazard analysis, poor start-up planning and poor emergency response

• Runaway Reaction: After synthesizing a Dekon, excess liquid was removed from the “cake” in a N2-inerted filter dryer. An agitator was used to smooth the cake to remove the liquid. The agitator had loosened and rubbed a plate at the vessel bottom, generating heat and hot spot. The vessel exploded, due to runaway decomposition at 138°C releasing flammable gases. The vessel pressure went up blowing open a discharge door. Gas and Dekon dust ignited, causing an initial weak explosion. Then a rupture disc opened with a second larger explosion. Incomplete knowledge of the hazards and runaway reaction. CSB

• Polymers: Solution of di-amines and di-carboxylic acids sent through a series of reactors. Partially reacted waste diverted to a catch tank. Due to problems with an extruder downstream of the reactor, a start-up was aborted. Unusually large amount of partially-reacted material reached the catch tank. Hot molten polymer in the catch tank continued to react and decompose, releasing gas and foam. Foam filled the tank and reached external pipes and vents. Catch tank was under pressure. When operators, unaware of the inside pressure, partially unbolted its cover, it blew off rupturing nearby piping. Hot fluid ignited. Fire. Blocked piping - unable to read tank pressure and fouled/ blocked RV inlets

• Runaway Reaction: Dye Production. Runaway reaction blew the reactor hatch. Violent explosion and fire. Inadequate cooling. Undersized rupture disks. No temperature or pressure alarms, automatic shut- down facility or dump/quenching reactants