MAYWOOD (CBSLA.com) — Authorities will continue air testing Thursday in Maywood, where an explosive warehouse fire forced the evacuation of about 300 residents.

Crews continued working early Thursday to ensure there were no lingering health risks before allowing those displaced to return. Residents who live on the south side of 52nd Street were allowed to return back to their homes Wednesday night, but those who live on the street’s north end, closer to the site of the blaze, were not yet allowed to return to their homes.

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Many of the evacuated residents sought shelter at the Maywood YMCA. A sheriff’s official said 138 people spent Tuesday night at the shelter. About 60 were allowed to enter their homes Wednesday to retrieve some needed items.

The three-alarm fire in the 3500 block of Fruitland Avenue, which was essentially extinguished Wednesday, ripped through a pair of commercial buildings early Tuesday, sparking a series of strong explosions and sending a thick plume of noxious smoke over a large swath of Southern California.

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One of the buildings that caught fire was a metal-recycling plant. Oxygen from the water being used to fight the fire created a chemical reaction with the burning magnesium, one of the metals being stored at the facility, producing “fireballs” and setting off strong explosions.

Dangerous conditions imposed by “tons” of chemicals at the site hampered firefighters’ efforts to douse the flames, authorities said. Firefighters were ordered to use breathing apparatus because of the fumes from the magnesium and a number of other substances at the business, officials said.

A hazardous-materials team was sent to the scene, and officials from the South Coast Air Quality Management District were notified. The AQMD later issued a smoke advisory, saying odor from the plume of smoke was prompting complaints across the region.

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