Thursday, March 7, 2013
Hwy. 78 closed to drain tanker
By SUE WATSON
A portion of U.S. Highway 78 was closed about seven hours Saturday as a precaution while a tanker containing liquid nitrogen was drained.
Hugh Hollowell, emergency management coordinator for Marshall County, said transfer of the liquid to another container was considered too dangerous because of damage to controls on the tank, caused by a tire that caught fire Saturday about 2:45 a.m.
Officials with Mississippi Emergency Management and the Mississippi Department of Environmental Quality were called for advice on the plan to discharge the nitrogen into the environment, he said. They were not on the scene, but officers with the Mississippi Highway Patrol, local law enforcement and local fire departments directed traffic.
Nitrogen is the major gas in the atmosphere and is not toxic, but liquid nitrogen is cooled to a temperature of under -200 degrees Fahrenheit and can instantly freeze tissues or asphyxiate a person if they do not have sufficient oxygen in the air, Hollowell said.
What was expected to take about two hours to off-load dragged on to about seven hours (from about 3 p.m. to 10 p.m.). He said the delay was because the outside temperature fell below freezing as nightfall approached – slowing the evaporation of the nitrogen cloud.
Hollowell said an empty tanker had been brought for transfer of the material, but experts decided not to try it because controls damaged by heat could fall apart, causing a rapid release of nitrogen into the atmosphere. He said this could have harmed those in near proximity of the several hundred yards radius that was deemed safe distance. And winds were up to 12 miles per hour and variable when the discharge of nitrogen was begun. Winds could have blown a nitrogen cloud into the eastbound land interfering with drivers’ vision, if the tank had been left open.
Experts decided to do a controlled release and set up traffic details to detour eastbound traffic at the Ingrams Mill exit and westbound traffic at the Victoria exit.
Some drivers complained of it taking up to two hours to get through the bottleneck, Hollowell said.
“The detail was a big team effort, that’s for sure,” said Maj. David Cook with the Marshall County Sheriff’s Department. “It took over an hour to coordinate the traffic control and the volunteer fire departments and local law enforcement did a great job in handling all that traffic.”
He said the temperature was below the freezing mark and the wind chill was about 25 degrees Fahrenheit during much of the seven hours of work.
The truck had pulled over on the shoulder of the westbound lane at mile marker 13, about two miles from the DeSoto County line. The tire caught fire, then caught the trailer afire. That was extinguished shortly after 3 a.m., but the trouble began when officials decided it would be too dangerous to transfer the nitrogen to another tanker, Hollowell said.
“We have certain protocols we have to follow when there is a potential release of chemical,” he said. “DEQ told us we had to release the product.”
Although the value of the liquid nitrogen was great, any potential accident could have cost much more and a risk/benefit assessment called for releasing the gas gradually from the tanker, Hollowell said.
He said the eastbound lane was closed because drivers could become disoriented if they drove through a cloud of the gas if the wind came from the wrong direction.
It was a grueling experience for firefighters, local law enforcement and state highway patrolmen who had to work in the extreme cold, Hollowell said.
“After it was all over, it seemed like much ado about nothing,” he said. “We had trained and qualified people from top to bottom and they all did their job very well.”
Forces were sent to warn people from several houses nearby about the release, he said, out of an abundance of caution.
Hollowell said the situation did not call for a Code Red if the system had been set up.
He said the procedure went well because of all the training that officers with law enforcement and fire department volunteers have had over the years.
“All the training we’ve done over the years paid off,” Hollowell said. “It becomes second nature sometimes.”
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