Abstract: A hazardous gas mixing apparatus includes a mixing chamber wherein air is mixed with such a gas to render same inert. An air inlet assembly admits an air flow induced into the mixing chamber and includes an air flow sensor having a probe located in a housing of the assembly. Differential air pressures detected by the probe are provided to a signal generating transmitter and signal converter serving a logic controller providing a display correlated to linear feet per minute air flow in the apparatus mixing chamber. A honeycomb air straightener serves to provide a laminar flow of air past the sensor probe. An intake screen on the housing reduces the intake of foreign particles.