Two people were hurt, one critically, in a New Cassel blaze that started when work done outside a large manufacturing plant ignited flammable aluminum, the Nassau County fire marshal's office said Monday afternoon.

A worker was in critical condition with burns at Nassau University Medical Center and a firefighter also was rushed there after his leg was fractured by falling duct work, said James Hickman, head of investigations for the fire marshal's office.

The blaze was reported about 1:30 p.m. at Oerlikon on Prospect Avenue, a business that uses flammable metals to make parts and coatings, authorities said.

The worker, 46, went outside to fix a malfunction in a duct and machine unit that sends aluminum powder, a byproduct of the company's metallic coatings and machine parts, into a drum, fire investigators said.

The worker was using power tools in the rear of the facility, Hickman said.

"It looks like he accidentally ignited some metal dust," he said.

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He was in critical but stable condition with second-degree burns over 25 percent of his body, including his head and stomach, Hickman said.

The firefighter, 27, a Westbury department volunteer, was in good condition just before surgery Monday afternoon, he said.

The Occupational Safety and Health Administration is investigating, the fire marshal's office said.

Special fire extinguishers, which spray a dry chemical, had to be used by the fire marshal's hazmat team, Hickman said. Certain metals burn "vigorously" and react "nastily" to water, he said.

A drum of aluminum powder also caught fire and the contents had to be dumped out so the fire could be put out, authorities said.

The fire was confined to the outside and five departments helped contain it at 4 p.m., authorities said.

Next door, the Nassau BOCES offices for adult education told dozens of staffers to leave early, said accountant Eileen Goroteuschek, who was answering phones: "Everybody was let go for safety reasons."

She said a "sour" odor was in the air outside. School was out for the year, and night classes were canceled.