In this Friday, Nov. 30, 2012 file photo, officials work the scene of derailed freight train tank cars in Paulsboro, N.J. Residents of Paulsboro were ordered to stay inside and schools were closed Monday, Dec. 3, 2012, after unsafe levels of the chemical vinyl chloride were found in the air near where the train derailed last week.

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(AP Photo/Mel Evans, File)

A containment boom floats in Mantua Creek Saturday, Dec. 1, 2012, near freight train tank cars that derailed Friday in Paulsboro, N.J. Residents in an area of about 12 blocks near the derailment remain out of their homes as officials continued their efforts to clear a hazardous gas that spewed from a ruptured freight train car. The precautionary evacuations were ordered late Friday, hours after a train derailment, and will likely remain in effect throughout the weekend and possibly longer. The order came after readings showed higher levels of vinyl chloride in the air. (AP Photo/Mel Evans)