A process transmitter for sensing a process variable includes a transmitter housing, a sensor, transmitter circuitry, a passageway and a flame arrestor. The transmitter housing has an interior. The sensor is disposed within the interior, senses a process variable of an industrial process and generates a sensor signal. The transmitter circuitry is disposed within the interior and connects to the sensor. The passageway is in communication with the sensor and extends through the interior of the transmitter housing. The passageway has a first cross-sectional profile. The flame arrestor is positioned in the passageway. The flame arrestor has a second cross-sectional profile different from the first cross-sectional profile. The flame arrestor produces a path in an interior of the passageway having a smaller cross-sectional area than that of the first cross-sectional profile of the passageway.