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Smoke from the Lake and Ranch 2 fires that were burning in the Angeles National Forest have caused unhealthy air quality in the Santa Clarita, San Gabriel and Pomona-Walnut valleys, as well as the San Gabriel Mountains, according to the South Coast Air Quality Management District.

“Stay indoors as much as possible,” Los Angeles County officials said in a tweet Friday.

The warning comes as Southern California enters a heat wave that is expected to bring dangerously high temperatures and raise the threat of wildfires.

The Lake Fire, which began in the Lake Hughes area of the National Forest on Wednesday afternoon, has burned 11,637 acres and is 12% contained.

While the Ranch 2 Fire had burned about 1,500 acres in northern Azusa and was 0% contained as of Friday afternoon.

Both blazes exploded in size shortly after they were initially reported.

“It is difficult to tell where smoke, ash or soot from a fire will go, or how winds will affect the level of these particles in the air, so we ask everyone to remember that smoke and ash can be harmful to health, even for people who are healthy,” Muntu Davis, Los Angeles County’s health officer said in a news release. “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.”

Officials suggest that residents avoid unnecessary outdoor exposure and limit physical exertion both indoors and outdoors when air quality is bad.

Children and those with air quality sensitive conditions, such as heart disease, asthma, and other chronic respiratory diseases, should stay indoors “even in areas where smoke, soot, or ash cannot be seen, or there is no smell of smoke.”

Officials are advising that day camps operating in smoke-impacted areas to suspend outside recreational activities until conditions improve.

Residents can do indoor activities in areas with visible smoke, soot or ash, as long as the indoor location has air conditioning that doesn’t draw air from the outside and has closed windows and doors.

If not, residents are asked to follow guidelines as if they were outside:

  • Avoid unnecessary outdoor activity to limit exposure to harmful air if you see or smell smoke, or see a lot of particles and ash in the air. This is especially important for those with heart or lung disease, older residents and children.
  • If outdoor air is bad, officials recommend keeping indoor air as clean as possible by keeping windows and doors closed. Air conditioners that re-circulate air within the home can help filter out harmful particles.
  • Avoid using air conditioning units that only draw in air from the outside, or that do not have a re-circulating option. Residents should check filters on their units and replace them regularly. Indoor air filtration devices with HEPA filters can further reduce the level of particles that circulate indoors.
  • If it is too hot during the day to keep the doors or windows closed and you don’t have an air conditioning unit that re-circulates indoor air, consider going to an air-conditioned place to protect yourself from harmful air.
  • Do not use fireplaces, candles, and vacuums. Use damp cloths to clean dusty indoor surfaces.
  • Do not smoke.
  • If you have symptoms of lung or heart disease that may be related to smoke exposure, contact your doctor immediately or go to an urgent care center. If the condition is life-threatening, call 911. 
  • When smoke is heavy for a prolonged period of time, fine particles can build up indoors and might not be visible. Wearing a mask may prevent exposures to large particles, but most masks do not prevent exposure to fine particles and toxic gases.
  • After a fire follow the ash clean-up and food safety instructions at available here.