Around 100 firefighters fought a serious fire at a 56,000 square-foot bio-diesel and chemical plant in the US last month.

The blaze at the plant that is home to American Biodiesel Energy Inc. and North American Powder Coatings in Erie, Pennsylvania, took six hours to get under control on 14 May. Firefighters then fought to extinguish it for another four hours.

According to local news, 26 firefighters sought medical treatment after being exposed to a mixture of at least nine chemicals.

Crews were then called back to the plant over the next couple of days after flames rekindled in portions of the building, local news reports said. It is not clear what started the fire and an investigation has been launched.

Fairfield Hose County chief, Jim Hawryliw, who is leading the investigation, said the biggest concern was how many chemicals were in the building. It is thought it contained vegetable oil, glycerin, ethanol, methyl hydroxide, tolvene, sulfuric acid, dry lye, powder coating and sodium methoxide, but that there may be more. He told GoErie.com:

"I believe there could be more chemicals in there. I believe the list we got was nine, but I think every day you go in there, you'll probably find something else. That's what our biggest concern is.

"We've been to that plant a lot over the years, with all the chemicals, and we were just never sure exactly what's in there,'' Mr Hawryliw said. "It's been ongoing for 30 to 40 years. That was always the building we were afraid was going to burn for the simple fact that there are so many chemicals in there.''