A fire that raged at SIMS Metal Management in Redwood City for nearly 17 hours is completely extinguished.
But the blaze that led to a "shelter in place" call also has left lingering health concerns due to the heavy smoke that spread throughout the area.
SIMS Metal on Monday told NBC Bay Area they are unsure what exactly was burning, and think it may have been paint, plastics and other parts of cars and appliances.
Officials are concerned that the toxic plume of smoke shot into the air may have contaminated the area's water supply with dangerous chemicals.
In addition, there is also concerns over the area's air quality.
An air rating of "35" is the maximum safe level by federal standards.
The Redwood City monitoring station during the blaze measured levels well above 100.
During Sunday's fire, smoke initially blew in a southwesterly direction and anyone who could smell the smoke was urged to shelter in place. The advisory was lifted around 6:20 a.m. Monday.
The warning for people to stay inside was extended to parts of three counties -- San Mateo, Santa Clara and Alameda.
Authorities said the blaze started at around 1:20 p.m. SIMS Metals is located on Seaport Boulevard. The fire was originally expected to be extinguished in three hours.
Hours after the flame broke out, the smoke began settling miles away, in places like downtown Menlo Park.
A nearby academic tutoring center felt the effects of the fire. The director of the tutoring center, Caitlin Tierney, said she took action to protect the students.
"We didn't really notice anything was wrong until some parents came in around 4:00, saying 'smells funny outside,'" Tierney said. "We didn't think anything of it until we could smell it inside."
The tutoring center then began handing out masks, as students tried to keep working despite the intense smoke.
"It's a really strange smell," said Megan Anzuini, who works at the tutoring center. "It's almost like burnt rubber and it stings. It kind of burns your eyes a little bit. It's a combination of a smell and you can feel it. It's almost smoggy outside"
No injuries or fatalities were reported.
The same building caught fire back in 2007, and the fire then was strikingly similar to today's blaze. The facility shreds metal to ship overseas.