Bowie-Dick Test

• Bowie-Dick test has been widely used in pharmaceutical industries for the vacuum sterilizers.
• This test developed by J.H. Bowie and J.Dick.
• Bowie-Dick test is also called dynamic air removal test.
• This test is performing to verify heat penetration inside the chamber.
• Bowie –Dick test applied that the pressure and vacuum pulses.
• Sufficient to remove the entrapped air so as to facilitate
• The purpose of pressure and vacuum pulse is to effectively remove air (condensation gases) from the chamber because air is a bad conductor of heat.
• Bowie-Dick test demonstrates proper air removal from the chamber of a pre-vacuum autoclaves.
• If air pockets are present inside the chamber the it would be verify difficult to sterilize the load.
• Pockets of a cool air act as a barrier that prevents steam from penetrating the load.
• Therefore, the air must be removed by a vacuum.
• Heat penetration can be checked by observing EN ISO 11140 Class-2 chemical indicator (Specific test indicator or Bowie-Dick Test Indicator) sheet which is used for this test.
• If colour change of the indicator sheet is uniform then it means air has effectively removed from the chamber and no air pockets left inside the chamber during sterilization.
• But if colour change is not uniform then it means these pulses are not effective to remove all air and air pockets from the chamber.     
• In the past time, Bowie-Dick test was performed by using layer of towels having an indicator sheet in between the towels.
• These towels were placed near the door and over the drain point, which would be considered as cold spot of the autoclave.
• But now a days this towel concept has been replaced by the Bowie-Dick pack.
• Different companies provide different Bowie-Dick test kit but the purpose of all these kits it to check heat penetration inside the load.
• As per HTM 2010 guideline, it is also called standard test pack. Total weight of the pack should be 7.0 ± 0.7 kg and height of the pack should be 25 cm or 250 mm.
• This test has to be performed on daily basis as per HTM 2010 guideline.
• The basic principle of this test is that when we run the Bowie-Dick cycle air is removed from the chamber and all air trapped inside the Bowie dick pack which we place near the over the drain point of the autoclave.
• The test pack is place in an empty chamber on the lowest spot (cold spot) above the drain.
• This sterilization cycle typically consists of three to four pre vacuum pulses. Each of which involve injecting steam in to the autoclave and then pulling on the air and steam through a vacuum,reaching the set point.
• Manufactures recommend running a Bowie –Dick test before you sterilize  your first load of the day.
• If air removal is effective than heat penetration will be proper and there will be uniform colour change of the indicator sheet.
• If air removal is not effective then colour change will not be uniform.
• There are different type of Bowie-Dick test packs available in the market.
  
• For example one of them is a set of paper sheets in pack and middle of these sheets there would be a chemical indicator sheet.
  
• To use this type of Bowie-Dick pack just place the pack as such over the drain point, no need to maintain the weight and height of the pack.
• Another one is having a S.S holder which can hold a bunch of sheet and in the middle, indicator sheet would be there and that pack has to be placed over the drain point.
• This one provide the required pressure on the pack (weight) and required height is maintained by the SS holder.
  

Common causes for failure of a Bowie-Dick test.

• It’s the colour change that tells you the steam is penetrating the test pack and pulling the air out of the autoclave.
• A successful Bowie-Dick test is very evident based on the colour change of a thermochromatic paper within the test pack.
• Thermochromatic ink was used in Bowie-Dick indicator. Thermochromatic ink is a type of a dye that changes colour when temperature increase or decrease.
• If the thermochromatic paper turns completely black,then the steam has penetrated the load and the autoclave is operating correctly.
• If the Bowie-Dick should fail, autoclave and the laboratory facility utilities should be checked. Any pre-vacuum cycle should not be used with any confidence until the test is repeated with a passing result.
• Lack of  or  a partial colour change indicates an unsuccessful Bowie-Dick test cycle. If the colour hasn’t completely change, it means something hasn’t worked correctly.

Related: Classification of Chemical Indicators

S. No	Cause of Failure	Description	Possible Solution
1	Air Leak	If air is able to leak into the autoclave chamber, the steam will be unable to penetrate the load to the point of total sterilization.	Run a  vacuum Leak Test  to further determine if an air leak exists or not.
2	Unwanted Condensation	Occasionally condensation will get trapped in the jacket of the autoclave, which can lead to cold spots at the base of the autoclave.   This could also indicate a wet-steam issue.	Check the steam traps on the autoclave. Check steam quality and wetness.
3	Faulty test Pack	From time to time, a Bowie-Dick Test pack can be faulty.	Check the expiration date and make sure the packs are being stored in the proper environment.
4	No Warm-Up Cycle	A warm-up cycle allows the sterilizer chamber and jacket to reach temperature.	Run a 5 minute sterilization cycle prior to running the Bowie-Dick Cycle.
5	Incorrect Procedures	Test packs work under very specific conditions.	Test packs should be placed in an empty chamber directly over the drain on the bottom rack or shelf. They are designed for use at 250°-273°F (121°-134°C).

Related : Vacuum leak test