The 5-day period is not a regulatory limit. Therefore, a facility may use a shorter or longer period if their situation calls for it. The number of days needed to establish the operating levels depends on the time it takes for the processor to reach chemical equilibrium or a "seasoned" status. In practice, this is usually achieved when the chemicals in the developer tank have been replaced or "turned over" 2-3 times.
For a given film, this time is a function of the developer tank size, the replenishmen rate, and the number of films processed (patient volume). Also, different film emulsion types have different replenishment rates per sheet of film, thus requiring different periods for the same processor to reach a seasoned status.
Based on experience to date, we expect the majority of facilities to use up to a 5-day averaging period. However, if a facility uses a longer period, it should provide empirical data or recommendations from the film manufacturer explaining the reasons for the longer time period. Regardless of the length of time needed for establishing or re-establishing operating levels, the facility must document the MD, DD, and B+F values daily. Even though there are no regulatory action limits during this period, monitoring of processing conditions is still important as these values may identify problems with developer temperature, replenishment rates, and other variables.