Train cars leaked corrosive hydrochloric acid after a Saturday derailment . Chemical spill caused a toxic cloud to form above Lafayette site . Score: 6 Lafayette authorities evacuated about 3,500 homes and businesses .
Train cars leaked corrosive hydrochloric acid after a Saturday derailment . Chemical spill caused a toxic cloud to form above Lafayette site . Exposure to the chemical can irritate skin . Lafayette authorities evacuated about 3,500 homes and businesses .