CONYERS — Federal authorities have found that a Georgia company improperly stored hazardous chemicals before a fire southeast of Atlanta last year that produced a toxic chemical cloud over the area. The Sept. 29 blaze at the plant in Conyers led to the closure of a major interstate, classes canceled for schoolchildren and forced thousands of residents to shelter in place as the chemical cloud moved around Atlanta's suburbs. BioLab Inc. was cited for six violations, including four serious violations, and now faces more than $60,000 in proposed penalties, the U.S. Department of Labor said in a statement this week.