Abstract: A lifting medium for an LTA craft is disclosed which includes a mixture of hydrogen and a quench gas which has a fire extinguishing action. This quench gas may be CF3Br, CF2ClBr, CF3—CHF—CF3, CHF3, C4F10, CF3CF2H, CF3CH2CF3, CF3I, CHClFCF3, or a mixture of two or more of these. An LTA craft buoyed by this lifting medium is also disclosed. The LTA craft may comprise an envelope comprising a main chamber, a vent chamber generally above the main chamber and separated therefrom by a separating membrane, and a first pressure relief valve opening between the vent chamber and the external atmosphere, which opens at a certain first threshold pressure.