A source storage server receives various write requests from a set of clients, logs each request in local memory, and forwards each log entry to a destination storage server at a secondary site. The system identifies a first prepaid gift account associated with a first prepaid gift. The first PFD is stable when a reference signal, supplied to a polarity determining flip-flop, leads the signal to be synchronized. The contaminated purge gas is removed from the device and the process is continued until the contaminant concentration in the contaminated purge gas is below a predetermined level.