The probable cause of an explosion aboard barge IB1940 on November 4th 2019 on the Chicago Sanitary and Ship Canal, Illinois Marine Towing facility, Lemont, Illinois, was owner J O Equipment’s incomplete procedures, which had failed to incorporate the safety instructions included in the Facility Operations Manual regarding the electrical bonding of air movers to barges, the National Transportation Safety Board (NTSB) has found. Thincomplete procedures resulted in an unbonded air mover being operated in a cargo tank with residual acetone, thereby causing a static electrical discharge, which ignited flammable vapours in the tank.
In its Marine Accident Report the NTSB said that the probable cause of the explosion was incomplete procedures that did not incorporate the safety instructions included in the Illinois Marine Towing Facility Operations Manual for electrical bonding of air movers to barges.
The barge was declared a total constructive loss, valued at $1.75m, but no-one was injured and no environmental damage was reported.
The Chicago Sanitary and Ship Canal is a waterway linking the south branch of the Chicago River with the Des Planes River at Lockport, Illinois. The canal is 30 miles long and has a minimum width of 160ft, a minimum depth of nine feet, and two locks.
The explosion occurred when the barge was being prepared for cleaning after its cargo of acetone had been unloaded.
IMT had been contracted to remove any residual acetone from the IB1940’s cargo tanks, ventilate the tanks, and wipe down any wet spots inside the tanks in preparation for the next load of cargo, which was scheduled to be crude ethanol. This procedure was referred to as a “strip-and-blow cleaning,” says the NTSB report. The stripping process was to be performed using a vacuum truck connected to stripping lines (pipes) aboard the barge to extract residual liquids from the barge’s cargo tanks.
The blowing process was to be performed using venturi-type air movers, powered by compressed air, to force fresh air into the cargo tanks and expel any residual vapours. These air movers had no moving parts and were typically used for ventilating hazardous areas. At the IMT facility, filtered and dried compressed air was provided to a manifold that ran down the length of the dock, with valve connections for flexible compressed air hoses at various locations on the dock.
Based on a nearby facility’s video showing the explosion near the centre of the barge in the vicinity of cargo tank 2 and the most severe damage to the barge found in that area, cargo tank 2 was the likely location of the initial explosion.
The source of ignition was most likely a static electrical discharge from the air mover that was resting on the painted dogs of the tank-cleaning access hatch of cargo tank 2. The technician who installed the air movers could not recall if they had been bonded to the barge (ensuring that the air mover was properly bonded to bare metal on the barge) but did recall that they had not been tied off to prevent movement.
Post-accident testing indicated that resting the cast aluminium bell of the air mover on the four painted dogs of the tank-cleaning access hatch without proper bonding did not provide good electrical bonding between the air mover housing and the barge. An inadequately bonded air mover would allow the accumulation of electrostatic charge generated by the flow of the compressed air stream with water droplets and rust particles. Without a proper bonding connection, a static electrical charge would likely not safely dissipate to the grounded barge, but could instead accumulate, causing a potential spark hazard.
The explosion occurred soon after the air movers were started and before the residual acetone was completely removed from the cargo tanks. When the first technician found acetone in the cargo tanks, he did not record his findings in writing but instead reported them to the shipyard superintendent verbally; the liquid barge manager stated that he was told there was no acetone left on the barge to strip. The quantity of residual acetone remaining in the cargo tanks was not properly communicated amongst the workers, and the air movers should not have been started before the tanks were verified to be completely empty.
The air movers used aboard the barge IB1940 on the day of the explosion had been recently acquired by IMT, had not yet been put in service, and were not inspected before use on the day of the explosion. Proper inspection of the air movers could have identified operational issues with the air movers such as loose connections and/or issues with the bonding straps. The procedures that were being used by IMT at the time of the accident and were identified in attachments of the Facility Operations Manual did not include the warnings about properly bonding the air movers. Even if there had been adequate procedures, the workers assigned to cleaning the IB1940 did not review the SOP prior to commencing cleaning operations. If the air movers had been properly bonded to the barge, the risk of a static electrical discharge would have been significantly reduced. After the accident, IMT updated their SOP to include equipment inspection, bonding procedures, and verification.
The NTSB’s investigation revealed that while Illinois Marine Towing had written guidance to workers for tasks related to barge cleaning operations before the explosion, the documents did not include all procedures identified in the Facility Operations Manual, specifically guidance for bonding air movers to the barge.
Following the accident, says the NTSB, Illinois Marine Towing updated its standard operating procedure for liquid barge strip-and-blow cleanings to a 13-page document that includes instructions for stripping tanks, verifying that all residual product has been removed from tanks, inspecting air movers before leaving the shop, and ensuring the bonding strap is attached and tested for electrical continuity between the air mover horn and the bonding clamp.