WILLISTON, N.D. (AP) — A more efficient system must be established to alert residents of danger in North Dakota's booming oil patch, an emergency manager and residents said, after authorities failed to alert the public for more than six hours when a facility storing toxic chemicals exploded. The fire was the latest of a lengthening list of incidents involving the state's booming energy sector, including oil train explosions, saltwater spills and fires at facilities caused by lightning strikes. Nicole Clarys, who works alongside Volesky near the scene of the fire, said she learned about the situation through Facebook, where many oil patch residents shared photos and videos of the blaze and explosions. On Wednesday, North Dakota Department of Health Air Quality Director Terry O'Clair said air quality tests conducted by his agency and the federal Environmental Protection Agency in Williston after the fire did not find worrying levels of contamination, as was initially feared.