The report describes different underground systems including mines and tunnels during construction (tunneling). The key factors that affect fire development in underground systems are described. Proposal and recommendations for ventilation strategies in case of fire are given. The report covers both fuel- and ventilation-controlled fires. In general, a minimal ventilation limits the fire growth and may even inert the fire through ascended smoke. A minimal ventilation also contributes to improved conditions for a first fire extinguishing attempt and evacuation.