WILLIMANTIC — Conditions near the scene of a massive Willimantic waste facility fire continue to improve as favorable winds helped dissipate a curtain of smoke that hung over a portion of the city for nearly a full day.

As dawn broke Monday morning, hazy smoke still filled sections of West Main Street near where firefighters continued excavating tons of smoldering debris pulled from the two-story Willimantic Waste Co plant that went up in flames Sunday.

But as the winds shifted and freshened, the pall of smoke lifted, giving clear sightlines along the road for the first time in nearly 24 hours.

Willimantic Fire Chief Marc Scrivener said firefighters made “significant” progress in tamping down the fire that destroyed the 100,000-square-foot building.

“The plan is to bring in heavy equipment and pull out all that construction debris and trash,” he said. “That will allow us to go deeper in. It’s still a dynamic situation but we're in the overhaul phase."

No cause for the fire has yet been determined. Matt Vertefeuille, the town’s public information officer, said the trash facility had a working sprinkler system at the time of the fire and the building was up to code.

In 2012, the U.S Occupational Safety and Health Administration levied a $17,050 fine — later reduced to $11,270 — on the company after an inspection prompted by an employee compliant, according to a public records search. The agency noted eight violations, including three "serious" safety issues. No accidents or injuries were reported as part of the investigation.

Scrivener said he expected a "skeleton" crew to stay on site overnight to keep an eye on potential flaring hot spots.

Crews from 14 area fire departments spent hours on Sunday dousing a stubborn fire fueled by 50 tons of wood scraps and assorted trash stored at the facility.

“We deemed the fire under control just before 6 a.m., but it’s still a very active scene and will stay that way for probably the next 24 hours,” Scrivener said.

Town and fire officials praised the quick response and endurance of firefighters working in challenging conditions.

“They were working six hours on, six hours off and six hours covering the city,” Scrivener said. ‘At one point we did need to call in extra resources to keep our oxygen bottles filled.”

The city used roughly 2.5 million gallons of water on the fire since Sunday, the majority of which ran off into the nearby Willimantic River.

Town officials late Sunday opted to cancel classes at local schools as heavy smoke drifted out in plumes. Classes at nearby Windham Technical High School and Eastern Connecticut State University were also canceled on Monday.

“We were getting reports of smoke coming into buildings up in the hill sections and also into Windham Hospital,” Town Manager Jim Rivers said. “We anticipated students might suffer at least some discomfort, so we decided to close for the day.”

He said schools will likely re-open for Tuesday.

Rivers said testing conducted by the state Department of Energy and Environmental Protection has turned up no indication of hazardous materials in the air, though residents are cautioned to avoid drifting smoke.

Shawn Mawhiney, spokesman for the Hartford HealthCare system, which includes Windham Hospital, said two firefighters were treated Sunday for smoke inhalation and released.

“There was also a resident seen whose asthma was exasperated by the smoke,” he said. “She was also released.”

Despite the severe damage to the facility — only the building's outer steel frame is intact in places -  Willimantic Waste Co drivers were still on the road Monday morning, loading their trucks with trash and recyclables from neighborhood bins and from the surrounding state area.

Rivers said members of the DeVivo family, which owns the company, have been at the scene and there has been no interruption in service.

“These are the best folks you’ve met,” Rivers said. “They’re already trying to figure out how to best take care of their customers.”

In an emailed statement on Sunday, the family thanked firefighters for their work.

“Tonight we are grateful,” they wrote. “First and foremost we want to thank the first responders who have come from far and wide to assist us today, and will continue to assist in the days to come, we will never have the right words to thank you, we are forever grateful. To our employees and community at large thank you for your continued trust, we look forward to seeing and serving you tomorrow.”

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