A train transporting hazardous materials derailed on Tuesday in the southern U.S. state of Kentucky.  The accident raises new concerns about railway safety in the United States. 

Thick black smoke billowed from a derailed train near Louisville in the southern state of Kentucky. And the mildly toxic fumes from the burning hazardous materials spread across the immediate area.  Some 20 people were treated at local hospitals.

Jeremy Urekew, an Emergency Management spokesman, said, "They are going to cause some irritation to anyone that breaths them in but as far as severe environmental hazards, we're not looking at anything really big."

The accident in Kentucky could have been far more serious.  Last year, the Federal Railroad Administration says there were more than 600 rail accidents in the United States involving hazardous materials.  Dangerous chemicals caused problems in only 20 of those accidents, but concerned government and industry officials say a railway accident -- or worse, a terrorist event -- in a major city could prove catastrophic.

In Washington, lawmakers are working with federal, state and local officials, and with the rail and chemical industries, to improve rail security.

Their concerns are twofold:  rail accidents and potential acts of terrorism. 

Robert Jamison of the Transportation Security Administration explains, "I think it's a worldwide problem.  As evident by the events in Madrid, London, and most recently in Mumbai.  This is a worldwide issue that people are dealing with. Terrorism against mass transit. Terrorism against rail infrastructure is a worldwide problem."

Those terrorists? attacks resulted in the deaths of hundreds.  It was only last July that a series of blasts killed some 200 commuters in Mumbai, the Indian city formerly known as Bombay.

Meanwhile, the U.S. government is working with the rail and chemical industry to develop stronger rail cars and new guidelines for transporting and tracking hazardous materials.