NTSB: Incomplete Safety Procedures Led To Barge Explosion
An October 13 report by the National Transportation Safety Board on a barge explosion last November highlights the importance of companies providing full and detailed instructions to their employees on safety policies and procedures. “Incomplete” safety procedures led to the explosion of barge IB1940 in the Illinois Marine Towing Heritage Slip near Lemont, Ill., on November 4, 2019, the NTSB report concluded.
The explosion occurred when the barge was being prepared for cleaning after its cargo of acetone had been unloaded. No injuries or pollution were reported. The barge was declared a total loss, valued at $1.75 million.
In the report, the NTSB said the probable cause of the explosion was incomplete written procedures that did not incorporate all of the safety instructions included in the company’s Facility Operations Manual for electrical bonding of air movers to barges. While Illinois Marine Towing had a three-page 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 electrically bonding air movers to the barge.
The barge IB1940, a double-hulled steel tank barge designed for bulk liquid products, built in 2013, had a cargo capacity of 11,558 barrels and was authorized by the U.S. Coast Guard to carry hazardous cargoes. It had three raised, externally framed cargo tanks and was equipped with a cargo pump, driven by a diesel engine serving all three cargo tanks. After discharging its cargo of acetone in all three tanks, the barge was shifted by towing vessel to the IMT Heritage Slip tank-barge-cleaning facility on November 2. It was scheduled for a “strip-and-blow” cleaning, with venturi-type air blowers with no moving parts used to evacuate vapors, after which the atmosphere was to be tested. Once declared safe, the tanks were to admit workers with rags to wipe up any residual wet spots. IMT had a three-page standard operating procedure to provide guidance.
According to the IMT liquid barge manager, acetone had been cleaned from various barges at IMT approximately 100 times. At about 7 a.m. on November 4, the liquid barge manager, a credentialed tankerman, assigned two liquid barge technicians and a new temporary worker to the IB1940 cleaning project. The workers reviewed and signed a “Table Topper-Every Day Reminder” checklist, which included items such as checking every void tank for water and odors, putting in all scupper plugs and ensuring two fire extinguishers were available and the emergency shower/eye-wash station and both the ground and winch wires were in place. The safety data sheet for acetone, which highlighted the dangers of the product, was also reviewed, particularly by the temporary worker, since it was his first day on the job.
According to the manager, the two technicians did not review the SOP because they were “seasoned guys” and they had done “a lot of stripping boats,” and the new temporary worker did not review the SOP because he was only to be serving in a support role (retrieving rags and tools) for the technicians and would receive introductory instructions about the barge.
After the morning meeting, the first technician went aboard the IB1940 and inspected the cargo tanks for acetone. He remembered estimating that cargo tank 1 had about 300 gallons of residual acetone in it, and cargo tanks 2 and 3 each had approximately 50 gallons in their sumps. These findings were not recorded in writing; the technician said he reported the quantities verbally to the shipyard superintendent. He said he told the second technician and the temporary worker to set air movers in place, but not to connect them. However, the liquid barge manager recalled that he was told that there “was no product on the barge to strip” and the technicians were going to start blowing air into the cargo tanks.
At about 9 a.m., the second technician and the temporary worker took from the shoreside shop three air movers, recently purchased by IMT. The air movers were used but had not yet been put in service by IMT. The technician did not inspect the air movers before use and could not recall if they had bonding straps attached to their frames before use. A bonding strap, when properly connected, is a physical connection between metal parts to ensure electrical continuity and eliminates the risk of electrical discharges that can create safety hazards such as arcing, fire and explosion.
The second technician placed a 6-inch-diameter air mover in the 18-inch tank-cleaning access hatch of cargo tank 3 by inserting the discharge horn into the tank and resting the cast aluminum bell flange on the inward-rotated dogs used to secure the tank. He attached the compressed air connection to the fitting on the side of the air mover.
On the pier, the temporary worker opened a valve on the manifold to provide compressed air to the air mover. The technician aboard the barge then placed another 6-inch-diameter air mover and compressed air was turned on; he then placed an 11-inch air mover in cargo tank 1, and compressed air was turned on to that unit. The technician aboard the barge also opened up each of the tank hatches to allow the air from the tanks to vent out. He could not recall if he attached the bonding straps to the barge but did recall that he did not secure the air movers in place with line during installation to avoid movement. After the three air movers were running, both workers went to the forward part of the barge to check the flanges and gaskets on the stripping pipe.
At 9:29 a.m., as the workers were stepping off the barge, they felt a vibration as the explosion occurred within minutes of the compressed air supply to the air movers being applied. Security video footage from a nearby facility captured the explosion and showed it was located approximately at the center of the barge in the vicinity of cargo tank 2. The workers ran to the IMT facility muster point and were directed to turn off the boiler, which was enclosed in a trailer about 60 feet from the stern of the barge. After hearing the explosion from the office, a shoreside worker called 911 and took a head count of the employees at the muster station. The local fire department arrived on scene and met with the manager. Together, they boarded the barge, which had a small fire at the base of each of the cargo tanks. Using two handheld dry chemical fire extinguishers through the holes created by the explosion, they extinguished the fires in each of the three cargo tanks.
A post-accident survey found that the barge IB1940 sustained extensive damage. The normally rectangular cross-section configuration of the raised cargo tank above the main deck had been bowed out in all directions. There was upward distortion of the tank top of about 5 feet over the barge’s entire length with numerous transverse tank-top stiffeners torn. Several holes were torn in the tank-top plating. After the accident, Coast Guard investigators found the air movers in various locations on the barge of the damaged IB1940. The two smaller air movers were found on top of cargo tanks 2 and 3, and the larger one was found on the port side of the barge outboard of cargo tank 1. The two smaller air movers did not have bonding straps attached to their frames, and the spring-loaded bonding (alligator) clamp of the larger air mover was engaged on the securing rope. It is unknown if the smaller air movers had been previously equipped with bonding straps.
In the days after the accident, the air movers in IMT’s shop were overhauled and outfitted with grounding wires. In a post-accident interview, the second technician stated that he had never completed a pre-inspection of the air movers and believed he had received some in-house training on establishing a proper ground by digging the ground clamp into the paint but did not recall any formal training.
Both the Facility Operations Manual and manufacturers of the air movers provided safety precautions advising operators to use bonding straps when operating in hazardous locations to prevent static electricity discharges. Also, air movers were required to be secured prior to admitting compressed air to prevent damage or injury from high-reaction force. At the time of the accident, IMT had written guidance to the workers for tasks related to barge-cleaning operations, but these documents did not include all procedures that were identified in the Facility Operations Manual, specifically guidance for bonding air movers to the barge. About two weeks after the accident, IMT updated the SOP for liquid barge strip-and-blow cleanings to a 13-page document, which included instructions for stripping tanks, verifying that that all residual product had been removed from the tanks, inspecting air movers prior to leaving the shop and ensuring that the bonding strap was attached and tested for electrical continuity between the air mover horn and the bonding clamp.
A fire and explosion investigator later stated that in order to provide an adequate bond, a cable (or strap) attached to the metal frame of the air mover would need to have a positive connection to bare metal of the barge. If a spring-loaded alligator clip was used, it would need to completely penetrate the paint layer and make contact with the bare metal of the barge. When inspecting the interior of the compressed air manifold at the facility, the fire investigator found a thin film of water and rust particles and indicated that “the flow of compressed air containing liquid droplets and rust particles would likely generate an electrical charge.” The fire investigation report further stated that this electrical charge could accumulate on the air mover if it was not adequately bonded to the barge. A spark of sufficient energy to ignite acetone/air mixtures could then be generated by discharge of the electrical charge stored on the air mover to the steelwork of the barge. The report identified the likely fuel for the explosion as residual acetone remaining in the cargo tanks and the likely source of ignition as a static electrical discharge from the air mover that had been placed in the tank-cleaning access hatch of cargo tank 2.
The NTSB concluded that the quantity of residual acetone remaining in the cargo tanks was not properly communicated among the workers, and the air movers should not have been started before the tanks were verified to be completely empty. Proper inspection of the not-yet-used air movers could have detected the lack of bonding straps, but the standard operating procedures then in use did not include warnings about checking bonding straps.
In January 2020, the Coast Guard issued Safety Alert 01-20, advising of the dangers of static electricity generated by air-moving equipment, which could discharge as an electric arc and ignite a flammable vapor/air mixture. The Coast Guard strongly encouraged that air movers should be properly electrically bonded to vessels, personnel should be trained on properly securing air movers in place to prevent movement, policies should be implemented for proper maintenance of air movers and supervisors should inspect the installation, bonding and securement of air movers before operation.
For more details, visit www.ntsb.gov and search for NTSB accident ID DCA20FM002.