A health caution was issued Valley-wide on Tuesday by the San Joaquin Valley Air Pollution Control District as smoke from the wildfires blazing around California drifted into Merced and surrounding areas.
"The health caution will remain in place and smoke impacts will continue until the fires are extinguished," officials said in a statement.
The Lion Fire in Tulare County, which was caused by lightening, consumed more than 12, 850 acres. The estimated containment date is on Nov. 27.
The Tubbs Fire in Napa County burned 27,000 acres as of Tuesday afternoon, according to the CalFire website. Also in Napa County, the Atlas Fire spread to 25,000 acres and the Patrick Fire burned up 1,000 acres. All three fires were burning out of control Tuesday, as were at least two other fires in Sonoma County.
Smoke from fires can cause lung disease, asthma attacks and increase the risks of heart attacks and strokes, Valley Air officials said. Young children, seniors and people with respiratory problems are "especially susceptible" to the health effects of pollutants from smoke.
"If you can smell smoke or see ash that is an indication that you should be treating air quality conditions as 'unhealthy' and remain indoors," according to officials.
People can go to www.valleyair.org/RAAN to check local air quality conditions.
As of Tuesday morning 15 people had been killed in the fires and officials said that number was likely to rise. More than 1,000 homes have been destroyed in the Northern part of the state.