Safety Alerts 4

Storage Tanks

• Fire inside empty LNG storage tank. Pressure hike lifted its concrete dome which then collapsed down inside the tank. Multiple fatalities

• Water ingress in Hot Oil Expansion Vessel led to boil off/ rupture/fire. Drain water at all low points drains during start-up. Potential source of water - one of the heat exchangers where the drain valve was not at the bottom. Consider oil as hydrotest medium to keep water out

• Water or light ends ingress in hot Bitumen storage tank has resulted in violent boil off/ rupture and fire. It has resulted in hot bitumen spray when a tanker truck with water was filled with hot bitumen 

• Tank Lifted Off: Pneumatic testing of tank piping without proper isolation. Leaking inlet valve. Positive isolation, a must

• Tank Lifted off: Upon a fire caused by a road truck hitting a nearby loading gantry, a 20’ dia tank exploded and lifted off 300’. Difficult to provide weak roof-to-shell seams for small tanks. BP

• Tank Blown off: Air blown into inlet line of a high melting point liquid tank. Its vent was choked with solids. Heated vent? WWW

• Soil: Insulated tank bottom corroded and spilled contents. Restrict insulation to 200 mm above base. Electrical heater below liquified C3= tank failed. Ground below froze. Uneven settlement led to leak. WWW

• FRP Tanks: In Sulfuric acid service failed under stress corrosion cracking. In Caustic Soda service failed when its PP lining leaked. WWW

• Steaming Out: After steaming out, tank was quenched with water to shorten cooling time. Vent was unable to cope and tank collapsed

• Explosion: Poor vapor freeing in connected tanks while doing hot work in one tank. A number of accidents continue to happen while welding “empty” tanks, with leaking valves (poor isolation) or not fully emptying light hydrocarbons or ignoring inter-connected tanks or ignoring high LEL readings. Flammable gas reached a tank under welding via a common overflow line without valves. Failure to follow Hot Work Permit procedures and/or purge (gas-free) before welding

• Poor vapor freeing: Naphtha tank vapor freed by filling with water and emptied. No flammable gas test done before welding. Residual naphtha in nooks and crannies - roof supports? vaporized. Explosion. Residues on a tank bottom initially covered by water caught fire. Small amount of acid left in an acid tank produced Hydrogen that exploded when welding started. Acid leak via a corroded steam coil produced H2 and explosion when 'steam’ line was welded. Acid under gas pressure sprayed out when pipe joints are broken in a few plants. WWW

• Welding Inside Tank: Air educator on a manhole was unable to sweep thru where welding area. The 10’ Oxygen monitoring wand handheld by an external watcher was far away to cover the welding area. BP

• Heavy oils: It is impossible to completely clean pipes, vessels and tanks that contained heavy oils or polymers. Tanks that were assumed clean have erupted in fire or exploded when welding torch heat vaporized oil ‘hidden’ in crevices or weld laps. WWW

• Water tank in a paper plant exploded and blasted off 375’ when there was hot work near the tank. The tank had turpentine, a solvent obtained from resin, contained in wood, during paper manufacturing. Caution: Even small quantities of organic liquids float on water and can form explosive mixture

• Alkylation process tank with spent sulfuric acid + HC. Hot work spark ignited HC via corroded holes in tank roof and shell

• Sulfuric Acid tank checked OK for explosive gas at tank bottom before repair. Hydrogen gas generated as a resulted of corrosive action had accumulated on tank top. Exploded when a grinder was used to cut rusted bolts

• Ink factory destroyed. Operator forgot to close a manual valve of steam heater in a mixing tank (heptane + propyl alcohol). No TAH/ TAHH. Vapor built up in the building and exploded

• Anaerobic bacterial decomposition of organic matter in empty tanks can produce flammable gas that can accumulate inside and explode

• River water was used as a water layer in a kerosene storage tank. Bacterial decomposition produced Methane that exploded. WWW

• Flush water may pass thru leaking valve and cause catastrophic reaction with chemicals in tank

• Caution while walking on tank roof. Corroded roof plates may yield. Icing can cause slip and fall, especially on cone roof. Have caused fatal fall/ drowning

• Passively failed LAHH can lead to overflow and fire. For volatile and flammable liquids, bunds around tanks are of no value, as the vapour quickly overflows the bund wall. LTs of LC and LAHH/LALL should track each other and give discrepancy alarm, to detect latent failure of trips. DCS also can estimate time to fill a tank based on initial level and pumping rate. 4 similar accidents

• Similar. Failed float and tape measurement led operators manually calculate likely fill time for a gasoline tank fed from a ship. No LAH/ LAHH. Resulting overflow led to VCE

• Static Electricity: High inlet piping velocity with sensitive stock like Naphtha. Static Electricity build up spark and fire. While loading a barge tanker with kerosene, explosion. Light ends with low electrical conductivity + flash point <20°C is hazardous. Air in empty tanks forms explosive mixture. Static electricity triggered by high fluid velocity + splashing in tanks. Dry air is slow to dissipate electricity. Steel pipes used as dead weight at the end of filling hose can spark

• Static Electricity: Condensate stored in crude tank. Leak and vapor cloud. Fire hose deployed for ‘water sweep’ triggered static electricity and ignition