An apparatus for transcutaneous treatment by gas, said apparatus comprising a rigid-wall cabinet arranged in a treatment room and having an upper opening and at least one openable panel, wherein a seat is arranged inside the cabinet, and the cabinet comprises at least one gas concentration measurement unit, and the cabinet further comprises a gas inlet for feeding the treatment gas and a gas outlet for discharging the treatment gas, a gas supply unit coupled to the gas inlet of the cabinet via a pipe and through an interposed controllable valve, and a gas tank connected to the gas supply unit, a ventilation unit connected to the gas outlet of the cabinet through an interposed controllable valve, a control unit for receiving the signals of the gas concentration measurement unit and for controlling operation of the valves (42, 63) and said ventilation unit based on at least the signals of the gas concentration measurement unit, wherein the apparatus further comprises at least one emergency sensor (26, 27, 28, 100), and the control unit is further configured to determine an emergency based on the signal of said at least one emergency sensor (26, 27, 28, 100); characterized in that the cabinet is not hermetically sealed, said ventilation unit is coupled via a further pipe to a space hermetically separated from the treatment room containing the cabinet, wherein said ventilation unit is a pump unit having a power suitable for removing, in case of emergency determined by the control unit, at least 90% of the volume of the treatment gas from the inner space of the cabinet to said hermetically separated space within at most 5 seconds. a rigid-wall cabinet arranged in a treatment room and having an upper opening and at least one openable panel, wherein a seat is arranged inside the cabinet, and the cabinet comprises at least one gas concentration measurement unit, and the cabinet further comprises a gas inlet for feeding the treatment gas and a gas outlet for discharging the treatment gas, a gas supply unit coupled to the gas inlet of the cabinet via a pipe and through an interposed controllable valve, and a gas tank connected to the gas supply unit, a ventilation unit connected to the gas outlet of the cabinet through an interposed controllable valve, a control unit for receiving the signals of the gas concentration measurement unit and for controlling operation of the valves (42, 63) and said ventilation unit based on at least the signals of the gas concentration measurement unit, wherein the apparatus further comprises at least one emergency sensor (26, 27, 28, 100), and the control unit is further configured to determine an emergency based on the signal of said at least one emergency sensor (26, 27, 28, 100); characterized in that the cabinet is not hermetically sealed, said ventilation unit is coupled via a further pipe to a space hermetically separated from the treatment room containing the cabinet, wherein said ventilation unit is a pump unit having a power suitable for removing, in case of emergency determined by the control unit, at least 90% of the volume of the treatment gas from the inner space of the cabinet to said hermetically separated space within at most 5 seconds.