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Washer/disinfectors are used in medical, as well as pharmaceutical applications, to either prepare goods for future autoclaving (for example surgery instruments to remove residues such as blood and protein) or to disinfect (semi sterilize) goods for later use.

In the case of steam sterilization the surface has to be properly cleaned. Without proper cleaning, sterilization is not possible. A clean and debris-free surface is required during steam sterilization allowing steam to contact all instrument surfaces.

It has been proven that bacteria can survive a steam sterilization cycle if they are protected under dried debris. When the washer/disinfection cycle is complete, the instruments can be inspected, placed in sterilization pouches or wraps and then properly sealed and processed in the sterilizer.

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A washer/disinfector can have various designs but usually they are a front operated cabinet with two levels. They typically contain a rotating spray system plus a glass door for inspection. The temperature will range from 40 to 100°C. The washer disinfector has the ability to wash, rinse, dry and disinfect the goods or instruments.


To document the conductivity, temperature, time and to calculate the A0 values the most suitable equipment would be Ellab’s wireless data loggers combined with versatile temperature and conductivity sensors. This makes it possible to measure 4 points at the top level and 4 other points at the lower level of the washer disinfector at the same time along with conductivity in the rinse water.

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The spray system makes it difficult to measure in a washer disinfector. When using measurement equipment with long cables it is imperative that these do not tangle into the rotating spray arm as this will break and ruin the equipment. Due to this, the usage of Ellab’s wireless data loggers would be the ideal solution.

Another point of consideration is the entrance ports on a washer disinfector. Often these units do not have any entry ports except for the front door. Choosing measuring equipment such as data loggers would be the best solution as no entrance ports are needed.

A third point is the ability to measure on the surface of instruments or the walls of the washer disinfector. It is here that flexible sensors are the easiest to mount and they give the most real and accurate measurements. Mounting the measurement equipment is really important as it is needed to know where the measuring tip has been placed. It is also important to avoid equipment being caught by the spray arm.


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A critical factor when validating any washer/disinfector is the calibration of measurement probes, especially temperature probes. Using the built-in calibration functionality, users can calibrate the Ellab sensors at regular intervals. The ValSuite Pro software generates an easy to read calibration report that includes all measurements and tolerances that are defined by the user. For Washer disinfectors an accuracy of +/-0.5°C or better is typically required. It is recommended that Ellab sensors and probes are sent in at least once a year for factory calibration (which includes a traceable calibration certificate).

Washer Disinfector Qualifcation

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All washer disinfectors require validation as a regulatory requirement. The requirement for testing or validating a washer disinfector unit is covered by the EN15883 standard. According to ISO 15883 a washer disinfector must undergo a validation process in connection with the purchase and installation to verify that it operates within preset limits when being used in accordance with the manual. The unit will also need to be revalidated on an annual basis, or when a critical component is replaced. Temperature tests are performed in an empty chamber and on a standardized load.

In an empty chamber:

  • One sensor in each corner => 8 sensors
  • One sensor on each side walls => 2 sensors
  • One sensor on center of roof
  • One sensor at automatic control temperature sensor

Conclusion: a minimum of 12 sensors are required.

The amount of measuring points is volume dependent. The more the load carries the more measurement points that are needed.

On standardized load:

  • 3 temperature sensors on each load carrier – at two diagonally opposite corners and in geometric center
  • 1 on each load carrier level to a maximum of 3 temperature sensors per carrier
  • 1 on slowest and fastest responding region overall
  • 1 sensor at automatic control temperature sensor and 1 at process recorder (if fitted)

Conclusion: a minimum of 9 (10) is required having only two load carriers.

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For qualifying the washer disinfector the A0 value is an important parameter. The definition of A0 is: Time in seconds at 80°C with a Z value of 10 to produce a given disinfection effect.

A0=600 for bacteria, mycobacteria, fungi and heat sensitive virus.

  • 6000 sec / 100 minutes at 70°C
  • 600 sec / 10 minutes at 80°C
  • 60 sec / 1 minute at 90°C

A0=3000 for heat resistant viruses (ex. surgical instruments)

Conductivity test is performed in the final rinse water.


When performing a validation of a washer disinfector, the main thermometric tests to be performed are an empty chamber (distribution test) and standardized load. Both tests have to be performed 4 times and the results from the last 3 cycles have to be proven identical by comparison.

The empty chamber tests have to be implemented first to find the coldest and hottest zone as the two zones have to be measured in the standardized load tests.

To document the homogeneity of the chamber it is good to use statistics, then it is possible to find maximum and minimum values and it is also beneficial to find the delta between maximum and average or average and minimum as the two values are good indicators for the distribution in the chamber.


With the knowledge from the empty chamber test, it is possible to continue with the standardized load test.

To document the disinfection effect of the washer disinfector and if the load consists of instruments, the measured temperatures have to give a higher A0 value than 600 or 3,000 depending on type of bacteria/virus.


Washer Disinfector Tests

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ValSuite® Software Reports

Washer Disinfector

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A0 Report
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Process Graph
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Unit Report
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