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As the Saddleridge Fire ripped through the San Fernando Valley, it sent thick smoke billowing over neighborhoods and ash filling the air for days while the flames raged.

The wind-driven blaze, which scorched about 12 square miles of land and damaged dozens of structures in its path, prompted the Los Angeles Unified School District to close dozens of nearby schools and dismiss students early at several others on Friday.

The district announced Sunday that almost all schools would reopen and resume regular schedules Monday after crews worked to replace air filters and clean the campuses affected by the fire.

But as some students and teachers returned to at least two nearby schools, they found ash covering their classrooms.

One teacher at Van Gogh Charter School in Granada Hills said she had to move her class outdoors after she walked into her classroom to find ash covering the desks and floors.

“The smell was absolutely atrocious,” the teacher, Lisa Bennett, said. “We have now got some cleaning crew here and they’re wiping down desks, but when we walked in this morning, there was ash on desks, there was ash on the floor.”

She described several people with watery eyes and scratchy throats.

Another teacher at Castlebay Lane Charter School in Porter Ranch said she saw ash everywhere and that carpets at the school were not properly cleaned.

“The school should have been closed today,” teacher Patricia Lingard said. “It is unhealthful conditions… the teachers are not feeling well and many of them have gone home.“

At one school, teachers were handing out masks to the students.

Some parents told KTLA they took their children out of class early and felt that the schools were putting their staff and students in danger.

One mother said she wouldn’t bring her kids back to school until it’s properly cleaned.

LAUSD said schools were ensuring the students’ safety by limiting outdoor activity as needed, running air conditioners in classrooms to filter out residual smoke, bringing cleaning crews back to schools and monitoring the fire and air quality to take appropriate action.

“At schools in the San Fernando Valley, maintenance crews worked over the weekend cleaning our schools and are returning this morning to provide additional cleaning support to ensure the safety and well-being of our students and staff. Students may be relocated from their regular classroom while this cleaning occurs,” a school district spokesperson said in a statement.

The district said that shifting winds may blow smoke into schools and that they were providing masks for students and staff who request them.

A smoke advisory was in effect through Monday for the San Fernando and Santa Clarita valleys, as well as the San Gabriel Mountains, according to the L.A. County Department of Public Health.

Wildfire smoke is a mixture of gases, water vapor and small particles, which can cause burning eyes, runny nose, scratchy throat, headaches and bronchitis. Those with sensitive conditions can also experience difficulty breathing, wheezing, coughing, fatigue and chest pain, according to the department

Health officials reminded residents that smoke and ash can be harmful to their health and advised them to limit outdoor activity and exercise.

“If you can see smoke, soot, or ash, or you can smell smoke, pay attention to your immediate environment and take precautions to safeguard your health. These precautions are particularly important for children, older adults, and people with heart or lung diseases,” county public health official Muntu Davis said.

The department advised schools and recreational programs in smoke-impacted areas to suspend outside physical education and after-school sports until conditions improve, Davis said.