Particle counting in reactive gases such as hydrogen and oxygen utilizing condensation nucleus counter (CNC) technology is now possible with counters such as the CPC 7651 being commercially available. Described here is a sampling system that allows these counters to be used for continuous monitoring in hydrogen and oxygen.

A closed sampling system is described which maintains the inlet of the particle counter at slightly above atmospheric pressure, utilizing sample gas pressure to maintain the proper sample flow rate. This avoids the use of a sampling pump which is a potential ignition source when used with reactive gases. For continuous monitoring applications, refilling of the working fluid during operation is necessary. A pressurized fill system is also described which allows a counter to be refilled against the elevated pressure at the sample inlet. The fill system provides an inert gas above the working fluid and can also be used to refill multiple particle counters.