Use
Anti-gas fans were described at the time as "... in daily use at the Front since May 1916; principally for clearing out shell-holes, mine craters, etc., of the foul gases that always accumulate in them under shell fire. These can now be cleared in a few seconds to a few minutes, and can, therefore, be consolidated immediately after capturing instead of having to be left for hours, and sometimes for days, before they can be entered. They are made of waterproof canvas."