This roof vent is made of UV-resistant, impact-resistant hard plastic and has an ingenious dual function. It is rotatable and can as a result be optionally used, as a ventilation and extraction system, in combination with a floor or side vent. As a result, permanent fresh air circulation flow is guaranteed, which fulfils the requirements of gas transport, in accordance with the DGUV. (German Statutory Accident Insurance Association).
For ventilation, the roof vent in the vehicle generates excess pressure, which pushes the heavy gases (e.g. propane) outwards through the floor vent, or as the case may be, the side vent.
For air extraction, however, an under pressure is drawn in of fresh air, by means of, the floor, or rather, side vent and light gases (e.g.acetylene) are pushed upwards and flushed out from above.
(pictures are similar, decorative material not included; delivery only within Germany)