In the hospital, bio-medical and pharmaceutical industries, in order to meet the requirements of the relevant guidelines (En 554, EN285, EN ISO 14937, EN ISO 17665, EN 876-3, HTM2010...) sterilizers and washers require validation on a regularly base.
Senze-Instruments provide first class services for thermal validation of :
- Steam sterilizers (steam and ethylene oxide)
- Sterilisation tunnels
- Cold chambers, blood banks, refrigerators, freezers
- Ovens, incubators, centrifuges
- Washer desinfectors
- Controls of the sterilisation and pastoration proces
The lethality value is the summation of the time/temperature integration calculated above a certain, minimum threshold temperature (Threshold). These are defined as the number of minutes which it takes to reduce the initial spore count of a certain microorganism to a desired safety level at a defined lethal reference temperature. The Fo, PU, and CV calculations are special calculations for food and pharmaceutical applications, where
Fo: Symbol for the sterilizing value which typically is equivalent to one minute at 250ºF (121.1ºC).
PU: Pasteurization Units. Lethality units used in a pasteurization process, where the Tx temperature typically is one minute at 140ºF (60ºC).
CV: Cook Value. Lethality units used typically in meat processing where the Tx temperature typically is one minute at 160ºF (71.1ºC).
All Madgetech lethality calculations are based on the General Method, also known as the Graphical Method, and are generally regarded as the most conservative lethality calculation. The Algorithm used for Fo, PU or CV is:
Madgetech Tracers also support Ao calculations (which use the same type algorithm with seconds instead of minutes as the time base).
Madgetech Tracers and Madgetech Reports use slightly different degrees of precision when calculating a Lethality value. There may be a small difference when comparing the two values, but this difference is normally less than the significant figures associated with the Final Lethality value and can therefore be ignored.
The temperature settings used in the various lethality calculations are easily defined in the constants text boxes. The lethality constant defaults are generally accepted “standard” values. If you have developed your own values, the factory defaults can be changed by overwriting the current value. These constants are:
Tx = Reference temperature. The lethality equivalent of one minute at Tx is taken as 1 unit of lethality.
Tp = Process temperature as collected by the Tracer.
Threshold = Minimum temperature below which no lethality will be accumulated.
z = Number of degrees required for the thermal destruction curve to traverse one log cycle.
While lethality can be confusing, the calculation in the Madgetech programs is easy to implement. Simply select the calculation you want (e.g. Fo), verify the constant values, and the calculation will be made for you automatically.