Safety Alerts 13

Flare

• Stack: Air Ingression. Reduced purge rate, incorrect suction pressure of an off-gas compressor, lower molecular weight + cooling of hot flared gas in stack resulted in vacuum with air ingression. Explosion at tip, ejecting parts and damage at stack base. IChemE

• Stack: Air Ingression. Styrene plant. Off-gas compressor with suction under vacuum. RD in suction had failed and 2 RVs were passing. Air ingression and explosion. Damaged stack base. IChemE

• Stack: Tip Ice Formation. Ethylene plant cold gas condensed steam injected at tip for smokeless combustion. Ice built up at tip, partially blocking package. Sudden thaw in the weather. Ice blown off. IChemE

• Stack: Guyed structure collapsed and leaned by 10°. 3m section buckled. Probable causes: Corrosion due to flare open drain line + Chlorides carried over from WSD. Localized holes in stack resulted in internal combustion and localized heating

• Boom. Flare boom fell into the sea during installation. Installation forces and methods

• Vent: Flame arrestors are subject to blockage with corrosion products etc. FA located on a cantilever boom in an offshore platform was plugged. No access to check, clean or replace. Tank started breathing via a sample hatch - a local release that ignited during hot work near the tank. Ruptured 2 tanks. Provide access to FA for periodical cleaning. Bypass with RD/ glycol seal are other options

• Vent: ¾” vent ball valve opened by falling debris. Flammable release. Fire. Cap or blind flange such vents

• Vent: Tip refractory debris + ice by condensate from the top steam ring blocked the stack. WWW

• Vent: Gas migrated along structural beam into MCC. Subsequent actuation of a pump relay blew MCC

• See IChemE paper Managing the Hazards of Flare Disposal Systems Analyzing Hazards

Drain

• OWS: Heavy rains spread light hydrocarbons floating on top of water all around the plant. Potential ignition and explosion.  Welding sparks in OSBL ignited HC in OWS, spreading fire. Box-in welding jobs over drains with fire resistant sheets and/or cover the drains

• SWD: Oil/ condensate floating on top provide a continuous fire path around the plant along the SWD routing. During rainy season, SWD can overflow spreading flammables. Usually, flash fires that are self-limiting once the oil/ condensate layer is consumed. May set up secondary fires that last longer

• H2S: Amine KOD drained to atmospheric sump via open sewer. While vacuum pumping out sump contents, its vent emitted H2S gas, exposing workers in the area. BP

• H2S: DEA tower was on maintenance and isolated. Drain valve that was not blinded, allowed backflow of sour liquid and H2S in the vessel. ALL lines, including drains, should be positively isolated. BP

• H2S: NaSH solution from spills during tanker unloading was collected in a pit connected to a sewer. H2SO4 was added to control pH of sewer flow to an Effluent Treatment Plant. H2S generated escaped via a gap in the sewer manhole. 2 fatalities and 7 injured. Study potential cross-contamination issues

• H2S: Released while transferring wastewater from a tank to a tanker truck by a vacuum pump. The H2S in the wastewater was supposed to be neutralized before transfer. There was no instrumentation to monitor H2S level in the wastewater. 1 fatality tanker driver

• Drain valve on tank outlet did not close properly, due to sludge accumulation. Valve was not blinded. Resulted in large oil spill

• VDU: Sample valve on cracking open, released 300°C vacuum residue that auto-ignited. Use sample cooler. BP

• VDU: No flow when drain valve was opened. A blockage suddenly cleared. Major release that auto-ignited. BP

• Light ends in drained liquid flash, chill and freeze water in the drain line blocking further drain flow. If operators assume that all the liquids are drained and leave the drain valve open, later the line may thaw and release HC liquid and vapor. Fire and Explosion. Check for icing

• Temporary flexible fiber-reinforced rubber hose melted while draining hot oil. Oil was above its auto-ignition temperature. Spray ignited. Fatality

• Caisson: Seawater entry into pipelines through open drain sump caisson system and pumped back into process can cause leaks and failure. SRB and Microbiologically induced corrosion (MIC)

• Caisson: H2 generated by depleted anodes inside caisson led to explosion. Vapor Corrosion Inhibitor added

• Static Electricity: Drained oil was collected in a metal bucket suspended from the drain pipe. Plastic sleeve on bucket’s handle resulted in poor earthing/ grounding. No metal-to-metal contact. Fire. BP

• API Separator: Carbon canisters to absorb hydrocarbon vapors got overheated and ignited the flammable mixture in the vent line. Nitrogen blanket/purge was insufficient. BP

Fuel Gas

• See Fired Equipment

• Corrosion Under Insulation (CUI): In fuel gas piping led to HC release and fire near a heater. Inspect insulated piping in close proximity to structures. Add inspection windows on insulation to monitor CUI. Apply first coatings on pipe 

• Hard piped (not flexi hose) compressor fuel gas piping came apart and was ignited by hot exhaust gas

• Poor quality 40” HP Fuel Gas test flange failed before reaching test pressure of 123 bar. Color code and identify test flanges used for hydrotest as to their rating

• Power plant fuel gas piping “gas blow” to remove debris was ignited and exploded. Use non-flammable purge gas

Heating Medium

• Carbon Steel tubes in Hot Oil Service are prone to corrosion leaks. Fire

• Check regularly hot oil samples for degradation that will indicate localized heating/ higher corrosion

• Flow maldistribution in a multi-pass heater led to coking and tube burst and fire

• Water trapped after hydro-test/ flushing expanded enormously when hot heating medium entered Expansion Tank. Rupture. “Steam explosion”. Consider oil as hydrotest medium to keep water out

• Nitrate salt used as heating Medium to remove heat from oxidation reactor leaked into a 36” pipe dead-leg with carbonaceous deposits. Exploded

Gas Turbine

• Hot air leaking from a bleed (air) line within enclosure ignited lube oil and diesel in the base of the skid

• Leaking lube oil within turbine enclosure formed an oil mist and caught fire on contact with hot exhaust manifold. Check regularly fuel and lube oil line within enclosure. Keep diesel fuel SDV at a safe distance from GT. Many cases

• 600 MW GT Generator. 2m long LP blade broke-off. Crashed thru the casing and roof 20m above. It took another 15 blades with it. Turbine-Generator shaft broke

• Water Mist System: Steam used to displace air. Poses scalding and asphyxiation risk if on automatic mode. Restrict entry

• Transport: Prior bridge strength and root survey not done. Bridge collapsed while truck was on it with GT

Electrical/UPS

• Short circuit between two or more battery banks of UPS. Likely caused by leaking electrolyte fluid contacting a conductive metal cabinet frame in UPS battery room

• Caution: While working in areas without pushbutton guards, one may accidentally start or stop machines or spill chemicals. BP

• Check for common cause failures that may make back-up power not available when main power fails. Primary and backup components should not be in the same place. Difficult to access during local fire

• While de-energizing circuit breakers inside a building, CO2 fire suppression system was activated. Lethal atmosphere and zero visibility. Fatality. Lock-out/ tag-out of CO2 cylinders not followed. BP

• Purged enclosures: Even air purged units may have N2 backup. Check O2 level before entering. Leaking purge may over pressurize an enclosure, leading to blow-off while opening lid/cover. Check PG for proper range

• Vapor tight lighting panelboard housings in non-hazardous areas have exploded when switches were operated. Flammable gases or vapors may travel through underground conduits/ conduit seals. Consider explosion-proof switches and arcing devices in such places. BP