CNN reports that 17,000 residents have returned to Apex, NC, after a fire at a hazardous materials plant forced them to stay away from home for two nights.

Environmental officials advise residents to clean off all surfaces, wash all clothing and bedding, and replace air filters upon returning home.

Officials still do not know what started the fire, but the main safety concern was Volatile Organic Compounds (VOCs) in the air. At least 44 people went to emergency rooms with breathing problems, and many pets left in the area experienced nausea and bleeding due to exposure to chlorine gas.