TUSTIN, Calif. (AP) — Parks and schools were closed Thursday in a Southern California city after officials found asbestos in the charred debris of an historic World War II-era blimp hangar.

The city of Tustin closed at least nine parks and urged residents to limit outdoor activities to reduce their exposure to ash after asbestos was detected in preliminary samples of ash and debris.

Schools were closed Thursday to ensure student safety in the Tustin Unified School District some 35 miles (56 kilometers) southeast of Los Angeles. A Veteran’s Day event planned for Saturday was canceled.

The blaze broke out early Tuesday at the massive wooden hangar, which was one of two built in 1942 by the U.S. Navy to house military blimps. The cause of the fire was under investigation.

Southern California air quality regulators will continue to analyze samples from areas around the hangar for toxic gases and metals, the city said in a statement.