German to English Tech/Engineering Mining & Minerals / Gems

I am translating a report on the adverse health effects of the isocyanates found in some compounds used for rock consolidation purposes in underground coal mining. In reviewing the possible connections between exposure to these compounds, either through skin contact or inhalation, and respiratory disorders, the author points out that some of the miners studied experienced breathing difficulties both while performing rock consolidation work (in which the suspect compounds are injected into rock under high pressure) and while working in the "abführenden Wetterstrom," which is said to carry a very low concentration of isocyanates for the very fact that it is an "abführender" Wetterstrom. I am familiar with the terms "ausziehender Wetterstrom" and "einziehender Wetterstrom," but I cannot document "abführender Wettestrom." My first guess was "exhaust airflow," but it would seem to me that the exhaust air would be even more heavily laden with these baneful chemicals. Can anyone with a background in mining terminology tell me what an "abführender Wetterstrom is in English?"
Thanks.