A flammable chemical that mysteriously appeared in Inner Harbor sewers - and may have been the cause of a manhole cover explosion Aug. 11 - came from the CSX Corp. train that derailed and caught fire three weeks earlier, the state said yesterday.

An independent laboratory has confirmed that the tripropylene found in underground storm drains matched that carried in one tanker of the 60-car freight train that derailed under Howard Street on July 18, according to the Department of the Environment.

The lab, Maryland Spectral Services of Baltimore, compared samples from the storm drain with a pure sample from the Louisiana supplier that loaded the original substance onto the train.

The result confirms what state investigators had recently suspected but not proved - that more than 2,000 gallons of tripropylene, a substance similar to petroleum, migrated through Baltimore's maze-like sewer system into the area of Light Street, where an explosion tossed a 300-pound manhole cover four feet into the air.

At about 78 degrees, tripropylene emits vapors that can be ignited by a spark or flame.

But department officials were unwilling yesterday to blame the manhole blast on the tripropylene from the train fire.

"We can't make any statement about whether or not the two are directly related," said Michael Sharon, chief of the department's emergency response division. "You've got gas lines, naturally occurring methane - a lot of other possibilities there."

Sharon noted that nearly 50 manholes have shot into the air this year in Washington, D.C. There, city officials have pointed to the crowding of underground electrical cables and outdated equipment as contributing factors.

In Baltimore, CSX has agreed to pay the tab - about $100,000 - for pumping the leaked tripropylene from the storm drains. But the company has not agreed to foot costs directly tied to the manhole explosion, nor does it accept responsibility, according to spokesman Rob Gould.

"We do not object to [the department's] findings with respect to the product in the storm drain matching the product that was in the rail car," Gould said. "However, at this point we do not believe there is conclusive evidence to indicate the product in and of itself was the cause of the manhole explosion."

Robert H. Murrow, spokesman for the city's Department of Public Works, said officials don't know how much the manhole explosion cost the city. Cleanup crews had to pump the chemical out of the storm drains, repair traffic lights that were disabled by the blast and reroute traffic for days.

"We are still in the process of tracking those figures," Murrow said. "We will have a final total ... probably the middle of next week."

Since the manhole explosion, workers have lifted more than 100 manhole covers between the Howard Street tunnel and the Pratt and Light streets intersection to look for more of the chemical.

"We've been all over the downtown area," Sharon said. He said "confidence is extremely high" that the chemical wouldn't be causing manhole blasts in the near future.

CSX is installing monitoring wells to sample soil near the Howard Street tunnel for tripropylene.

City and state officials had originally believed all of the chemical had been burned up in the train fire and derailment.

"It came as a surprise to us that there was enough of that material to get into the storm drain system," Sharon said.

Sun staff writer Caitlin Francke contributed to this article.