1982 - Chem 112

A ramming of a bridge as it opened occurred at 0300 hours on January 3, 1982 in pre-dawn fog conditions of Galveston's West Bay, U.S.A., as the tug Beth was pushing the barge (Chem112) and a second acrylonitrile barge eastwards along the Gulf Intracoastal Waterway at a speed of about 3 knots (see Figure 1 for accident location and scenario). The Intracoastal Waterway is a partly man-made and partly natural waterway which stretches about 1800 km from Florida to the Mexican border at Brownsville and connects the Gulf
ports with many U.S. cities via the country's river system.
Barges carried about 100 million tonnes of goods in 1982 on the Waterway, including refined oil products, grain, coal and petrochemicals. The low-slung bridge (with only a two-metre clearance between the water surface and the bottom of the structure) was being raised when it was hit by the Chem112, the first vessel in the small flotilla. Tow of the barge's three tanks ruptured on impact, spilling their contents. The flammable liquid in the first tank immediately ignited and exploded, followed within minutes by the acrylonitrile in the second tank. The blasts blew out the windows in the bridge control house. The bridge operator was taken to hospital for treatment of smoke inhalation and discharged after a few hours.

Acrylonitrile is a chemical intermediate used in the manufacture of acrylic fibres, plastics and elastomers. From a human hazard point of view, it poses a triple threat; it is highly flammable, toxic and polymerises violently. It has a flash point of 0°C which means that its vapour becomes flammable at any temperature above the freezing point. The vapour can also burn so rapidly that it appears to explode, especially in a confined area.

When acrylonitrile burns, hydrogen cyanide and/or phosgene gas. Fires of acrylonitrile can be extinguished by alcohol foam, dry chemicals and carbon dioxide.

Acrylonitrile is toxic in both liquid and vapour and can be lethal in high concentrations. It has also been found to be carcinogenic over long exposure periods. However, no permanent damage is considered to be caused by short-term exposures once a person recovers from the acute exposure.

Because of acrylonitrile's tendency for polymerising during transport and storage, an inhibiting agent is added to the liquid which temporarily prevents this reaction. If uninhibited, runaway polymerisation occurs and the heat liberated during the process may cause the chemical to explode, particularly if the liquid is contained.

If spilled into the marine environment, acrylonitrile will dissolve and evaporate.

A ramming of a bridge as it opened occurred at 0300 hours on January 3, 1982 in pre-dawn fog conditions of Galveston's West Bay, U.S.A., as the tug Beth was pushing the barge (Chem112) and a second acrylonitrile barge eastwards along the Gulf Intracoastal Waterway at a speed of about 3 knots (see Figure 1 for accident location and scenario). The Intracoastal Waterway is a partly man-made and partly natural waterway which stretches about 1800 km from Florida to the Mexican border at Brownsville and connects the Gulf
ports with many U.S. cities via the country's river system.
Barges carried about 100 million tonnes of goods in 1982 on the Waterway, including refined oil products, grain, coal and petrochemicals. The low-slung bridge (with only a two-metre clearance between the water surface and the bottom of the structure) was being raised when it was hit by the Chem112, the first vessel in the small flotilla. Tow of the barge's three tanks ruptured on impact, spilling their contents. The flammable liquid in the first tank immediately ignited and exploded, followed within minutes by the acrylonitrile in the second tank. The blasts blew out the windows in the bridge control house. The bridge operator was taken to hospital for treatment of smoke inhalation and discharged after a few hours.

Acrylonitrile is a chemical intermediate used in the manufacture of acrylic fibres, plastics and elastomers. From a human hazard point of view, it poses a triple threat; it is highly flammable, toxic and polymerises violently. It has a flash point of 0°C which means that its vapour becomes flammable at any temperature above the freezing point. The vapour can also burn so rapidly that it appears to explode, especially in a confined area.

When acrylonitrile burns, hydrogen cyanide and/or phosgene gas. Fires of acrylonitrile can be extinguished by alcohol foam, dry chemicals and carbon dioxide.

Acrylonitrile is toxic in both liquid and vapour and can be lethal in high concentrations. It has also been found to be carcinogenic over long exposure periods. However, no permanent damage is considered to be caused by short-term exposures once a person recovers from the acute exposure.

Because of acrylonitrile's tendency for polymerising during transport and storage, an inhibiting agent is added to the liquid which temporarily prevents this reaction. If uninhibited, runaway polymerisation occurs and the heat liberated during the process may cause the chemical to explode, particularly if the liquid is contained.

If spilled into the marine environment, acrylonitrile will dissolve and evaporate.

Immediately following the explosions, the crew of the Beth uncoupled the two barges from the tug which subsequently drifted back down the waterway and grounded on a shoal about 11/2 km away. About 20 minutes after the collision, the contents of the third tank ignited, but the second barge still attached to the Chem112 remained unaffected.

The U.S. Coast Guard and other officials at the scene decided that the best course of action was to free the two barges, allow the cargo to burn itself out and spray water on the second barge to keep it cool. At 07.30 hours, after the chemical had burnt for an hour and the situation was monitored to gauge the behaviour of the burning cargo, three Coast Guard personnel boarded the two barges to separate them.

After donning a gas mask, one of them boarded the barges from a patrol boat which had been manoeuvred into position on the upwind side. Within 15 minutes, the turnbuckles were disconnected and the wire ropes linking the barges unhitched. The second barge was pulled clear and Chem112 was anchored and its cargo allowed to burn.

Local authorities decided to evacuate 12 families even though they were relatively distant from the burning barge. The chemical company had personnel in the vicinity while the barge was burning, monitoring the atmosphere and the water for high concentrations of the substance. As no traces of toxic fumes were recorded, the evacuees were allowed to return to
their homes on January 4.

While the interstate highway across the adjacent causeway was only shut for two hours, it was to be five days before the damaged bridge, the only rail link between the mainland and Galveston and its port facilities were back in business. Fortunately, stocks in the port's grain elevators were sufficient to meet export commitments for the duration of disruption whilst trucks brought in some 15 percent of the container traffic normally handled by rail. It is also fortunate that the bridge had opened to the extent it had before impact since the entire drawbridge could have been knocked down.