Three derailed tanker cars continued to leak toxic chlorine gas Friday, making it unsafe for hundreds of area residents to return home, officials said.
A train derailment a day earlier forced evacuation of the nearby town of Alberton and sent more than 100 people to hospitals.
“We’re going to be in a 24-hour operation through Monday, probably, at a minimum,” said Homer Young, operations director for the state Disaster and Emergency Services Division in Helena.
The gas leakage was intermittent because of a continuing cycle in which interior icing temporarily seals the leaks before the warmer outside air temperature thaws them again, said Chris Hohol of Superior Services, a Wisconsin company that specializes in cleaning up hazardous spills.
There was no significant spread of the toxic cloud and the density of the gas at the derailment site was low enough to allow people to approach within about 50 yards without the need for protective gear, Missoula Rural Fire Chief Bill Reed said.
Scott Waldron, commander of emergency personnel at the scene, said some of the people who had been evacuated might be allowed to return to their homes briefly today to check on livestock and pick up clothing and other personal items.
Interstate 90, Montana’s principal east-west highway, remained closed near the site of the derailment, and traffic was routed along an 80-mile detour - a situation that might continue through Monday, officials said.
“There’s going to be a lot of pressure” from commercial interests to open the highway sooner but the decision will be based on health and safety, not on commerce, said Jim Greene, chief of the state disaster agency.
Eighteen cars jumped the tracks early Thursday, including five tankers that overturned, said Lynda Frost, a spokeswoman for Montana Rail Link, which operates the track. Three cars were leaching chlorine gas, a strong irritant that forms an acid when mixed with water.
Specialists wearing protective gear were examining the derailed cars to determine how best to empty the chlorine from the tanks. They said one of the cars had vented almost all of its 170,000 pounds of chlorine.
Missoula County officials said that 400 to 500 people living in Alberton, the town closest to the derailment, were evacuated. About 300 were spending a second night in Missoula, being fed and sheltered in motels at the railroad’s expense.
The toxic fog sent 105 people to hospitals, mostly because of lung irritation and breathing problems.
The two most seriously injured lived near the derailment site and may have been exposed to the chlorine gas for up to 45 minutes, said Drew Dawson of the state Health Department. St. Patrick Hospital in Missoula said Friday their conditions had improved from critical to serious.
Weather conditions that were nearly ideal for minimizing spread of the toxic gas Thursday - light rain and almost no wind - changed Friday as a cold front moved into the region and winds picked up, said Gina Loss, a meteorologist with the National Weather Service in Helena.
“There will be some movement (of the gas cloud) but it won’t be dramatic,” Loss said.