Abstract: An enclosure, for example, a safety enclosure around noisy or potentially dangerous machinery, includes a door which, when opened, stops the operation of the machine to prevent injury to personnel who may examine or maintain the machine. A pneumatic safety system for the door includes, in series, a source of compressed air, an air regulator valve, a series of disconnectable air connectors and a transducer, such as an air pressure limit switch, which converts a decrease in air pressure into a control signal to stop the operation of the machine. One air connector member is mounted on the door and another on the door frame, so that they are automatically disconnected when the door is opened, thereby opening the pneumatic line and causing the air pressure to decrease. The connector members each have a flat face which meet in a flush relationship, one connector member having a round orifice and the other connector member having a multi-slotted orifice which leads to an internal air cavity.