Analysis of particles that fell on a residential area near the Chempark industrial estate in Leverkusen contained no dioxins or polychlorinated biphenyls, environmental protection official Ulrich Quass told a news briefing.
The blast at the Chempark site, which hosts chemicals companies including Bayer and Lanxess, killed five people, injured 31, and set off a fire in a tank containing solvents.
Local residents were told to close their windows and stay indoors to minimize their exposure to the fallout. Officials said precautionary measures would stay in force while a cleanup operation went ahead.