Mine gas production in a closed coal mine
<a href="//commons.wikimedia.org/wiki/User:Sponk" title="User:Sponk">A. Müller</a> (<a href="//commons.wikimedia.org/wiki/User_talk:Sponk" title="User talk:Sponk"><span class="signature-talk">talk</span></a>)
CC BY-SA 3.0 de
based on <a href="https://en.wikipedia.org/wiki/de:File:Gasstill1.jpg" class="extiw" title="w:de:File:Gasstill1.jpg">a work</a> of <a href="https://en.wikipedia.org/wiki/de:user:Rasi57" class="extiw" title="w:de:user:Rasi57">Rasi57</a>