Air quality regulators will decide early Friday, June 30, whether to extend a smoke advisory for Orange County, after residents were urged to stay indoors Thursday as the Cristianitos fire spewed harmful particulates into the air.

The advisory is in effect through Friday morning, when the South Coast Air Quality Management District will again assess weather conditions and fire containment, said district spokesman Sam Atwood.

“We update the smoke advisories typically between 8 and 9 a.m.,” Atwood said.

As smoke from the approximately 760-acre fire at Camp Pendleton darkened the skies, early Thursday, the district and doctors said residents should avoid going outside, particularly children, older adults and those with respiratory and heart disease.

“There’s particulate matter in the air that can aggravate the lungs,” said Dr. Eric Handler, Orange County’s public health officer. “If you have an underlying problem with your respiratory system, it can magnify it. It can exasperate asthma as well as other conditions.”

The advisory, which also covered parts of Los Angeles County, warned that air quality could reach unhealthy levels in the Capistrano Valley area, Saddleback Valley and the central Orange County coastal area.

“If residents are seeing and smelling pretty heavy smoke, it’s quite likely that air quality is at an unhealthy level for everyone and they should take precautions accordingly,” Atwood said.

After the marine layer burned off and winds picked up, officials said, conditions improved by Thursday afternoon. The forecast for Friday calls for similar temperatures and marine layer conditions.

When smoke is present, Handler said, residents should remain indoors as much as possible. He advised running the air conditioner at home so the air is filtered; and when driving, using the recirculate setting for the air conditioner.

Dr. Sarah Field, an allergist at Children’s Hospital of Orange County in Orange, said her patients were experiencing more allergy and asthma symptoms because of the smoke, which can cause difficulty breathing, along with coughing, wheezing and shortness of breath.

She said patients with respiratory conditions should take their medications as prescribed and seek medical care if needed.

“Even with a healthy child, there’s no doubt it’s an irritant in the air,” Field said. “I think common sense prevails: Healthy or not, I think it’s well worth it to stay indoors regardless of your health condition.”

Field said smoke exposure won’t cause lasting damage.

“When the smoke clears, then the symptoms are short-lived,” she said. “At least there’s an end in sight.”

The AQMD said residents should take the following precautions in any area where smoke can be seen or smelled:

Children should stay indoors, along with older adults and those with respiratory or heart disease. Windows and doors should stay closed.

Avoid any vigorous outdoor or indoor activity.

Run the air conditioner and keep the filter clean to prevent smoke from coming inside

Residents can also sign up for customized air quality notifications at airalerts.org.