CHAPEL HILL - The Orange County Animal Shelter was locked down for 30 minutes Monday while some chemical cylinders found at an old university waste dump nearby were removed.

The cylinders, 6 inches across by 2 feet tall, contain compressed gas that could explode, but officials have not identified the cylinders' contents.

"These cylinders have been underground for a very long time," said Mary Beth Koza, director of environmental health and safety at UNC-Chapel Hill.

From 1973 to 1979, UNC used the site off Municipal Drive to dump waste chemicals. The shelter closed for a day last month when a remediation crew discovered 17 smaller cylinders, one containing the nerve gas phosgene. Officials don't think the larger cylinders contain the same chemicals.

Fewer than 10 employees were at the shelter when the cylinders were found Monday. They stayed inside with 200 animals until the tanks were removed.

The cylinders will be shipped out of Chapel Hill this week and incinerated, possibly in Texas, Koza said.

Bob Marotta, animal services director, said the shelter will continue to operate as normal until a new shelter opens on Eubanks Road later this year.