In many tunnels, safety equipment has to be fitted retrospectively in order to comply with statutory regulations. The cables which have been laid in the individual ducts must be exposed to enable this work to be carried out. For fire-prevention reasons, these ducts are filled with sand. The material is sucked out and transported to the storage area in a short time and without the risk of damaging the power and communications cables. On completion of the work, it can be reused.