Dear Madam/Sir,

I would like to request your advice on the following points.

Sub: Yellowish colour on the chamber walls of a Washer Disinfector This is regarding Yellowish colour on the chamber walls including the wash cart and the instruments which looks like rust.

1. The Washer Disinfector started to become yellow in colour along with the wash cart and the instruments after 7 months from its installation date.
2. The detergent used was Tripple Enzyms during Main wash at 50 Degrees Celcius for 5 Mins. Wetting agent /Rinse Aid (Zero Spot ) which is acidic was used during the Final Rinse at 93 Degrees Celcius for 10 mins. Result was that the Chamber, Wash cart and Instruments were Yellow in colour.
3. I used Phosphoric Acid also known as Dilac ( Descaling Agent) some 100ml during the Neutralising phase. For Main wash I used Detergent Alkaline base PH value 14 (Tripple Enzym was withdrawn), temp. at 45 degrees celcius for 3 Mins. Result: The chamber as well as wash cart and instruments were very clean without any traces of Yellow colour.

Now my question:

1. What is it that has caused the chamber to become Yellow?
2. What is the remedy?
3. Is it OK to use Phosphoric Acid/Descaling Agent? Or will it cause any harm to the Stainl-less steel chamber and the instruments.

I have attached some pictures for your attention.

Please Advice.

Regards,

Norberto Agnelo,
Kuwait.

Dear Noberto,

If the yellow colour took 9 months to appear and it sounds as if this was gradual it may give you a clue as to cause. I make certain assumptions from your question. If you did not change the surfactant brand over this period cause could be:

1. manufacturer of surfactant change in formulation.
2. a component in the pump circulatory system breaking down and giving rise to this colour.
3. the use of other complementory chemicals or change in use of such chemicals which may not be compatible with other products in use
4. can you see any surface damage on instruments [if they have plastic/rubber/polymer components] They may give up a yellow colour. Do you wash such instruments?

Only you know what happened over the last 9 months. You have a clue also by your reported change in the protocol which did not give you the yellow colour.

I do not think you will have a problem with 'corrosion' with phosphoric acid but careful inspection of stainless after a wash will tell you this by looking for a fine etching of the surface.

It is a difficult problem and with luck somebody else will have encounterd it and solved it. Manufacturers of the chemicals in use should be approached to help - direct or through distributors/agents you may be wise to press them for an explanation. Also press the washer maker for an explanation - they mey have encountered same.

Hope this has given food for thought

JIM DALY
M.D. for Medipure

www.processtech.co.uk worth a look!!

Dear Norberto

The yellow colour in your washer disinfector was iron oxide. The iron oxide is in your water supply and has nothing to do with the cleaning chemicals you used. Switching from an enzymatic cleaner to an alkaline detergent removed this discolouration.

I have come across this problem frequently in the UK and if you wish to switch back to an enzymatic cleaner. All you will need to add is a conditioning rinse cycle using Phosphoric acid on a daily basis.

Regards

Matthew Peskett
UK Distributor for the Ruhof Corporation.

Dear Norberto,

Based on my experience this discoloration can be caused by dried-up ingredients in water qualities, which are used for reprocessing of surgical instruments in washer disinfectors. These water ingredients can be either water hardness or silicates. A very thin layer of these dried-up residues of water ingredients is like a glaze and if it becomes thicker, the colour will change from yellow to blue. This discolouration is especially good recognizable on metal surfaces due to the reflection of light. These glaze like discolourations can be removed by use of acidic cleaners based on phosphoric acid or hydrofluoric acid and it can be prevented by use of an acidic neutralisation step as you have described in your request. Another way to prevent the discolouration of stainless-steel surfaces is the use of deionised water, which is free of silicates, for final rinse.
Now, I have got a question about the wetting agent, which you have mentioned. This rinse aid is recommanded for dishwashers bur are you sure that this rinse aid is also suitable for medical devices? If you want to continue the use of rinse aids for medical devices, we recommand rinse aids, which are especially designed for such medical devices like surgical instruments.

Best regards,
Dr. Jürgen Staffeldt
www.drweigert.de