PARKERSBURG, W.Va. — West Virginia emergency officials say federal guidance following the warehouse fire that smoldered for more than a week in South Parkersburg shows spikes in the soot initially detected in the air.

The blaze began early on Oct. 21 in the 420,000-square-foot (39,000-square-meter) property is owned by Columbia, Maryland-based Intercontinental Export Import Inc., which says it buys and sells an array of recycled plastics worldwide.

The federal Agency for Toxic Substances and Disease Registry says spikes in particulate matter occurred from after midnight until dawn the first day and ranged up to hazardous on its air quality index, meaning people with heart and lung disease, older adults and children should remain indoors.

It reports air quality improved the weekend following the fire, with air quality ranging from moderate to good.