The invention relates to an indoor safety device for a liquefied fuel gas system, the system comprising a storage device storing liquefied fuel gas; a vent member arranged in fluid communication with the gas inside the storage device; and a safety valve arranged to evacuate gas when the pressure inside the storage device exceeds a predetermined first value, the safety device comprising: a vent coupling; a pressure relief valve arranged downstream of the vent coupling; and a conduit for conveying gas, adapted to be connected to the pressure relief valve, the safety device being removably connected to the system by connecting the vent coupling to the vent member, wherein the pressure relief valve is configured to release gas when the pressure inside the storage device exceeds a predetermined second value, lower than the first value.