In situ respirator fit testing

A system comprising:

• a first condensation particle counter having a first inlet port, a first growth column, and a first optical element for counting particles detected at the first inlet port, the first condensation particle counter configured to provide a first signal corresponding to the particles counted at the first inlet port;
• a second condensation particle counter having a second inlet port, a second growth column, and a second optical element for counting particles detected at the second inlet port, the second condensation particle counter configured to provide a second signal corresponding to the particles counted at the second inlet port;
• wherein the first condensation particle counter and the second condensation particle counter are configured to include a wick in which the wick is wetted by water;
• a differential pressure sensor coupled to the first inlet port and coupled to the second inlet port, the sensor configured to provide a pressure signal;
• a processor coupled to memory and configured to receive the first signal, the second signal, and the pressure signal and generate an output corresponding to a ratio of the first signal and the second signal and correlate the ratio with the pressure signal;
• and
• a housing configured to receive the first condensation particle counter and the second condensation particle counter, the differential pressure sensor, the processor, and the memory.