WFHSS - World Forum for Hospital Sterile Supply

Conferences & Congresses [04/01/2011] Conference Calendar Update: Annual General IASSM Meeting 22 January 2011 22 January 2011 Dublin Dental School & Hospital, Trinity College, Dublin, Ireland
Courses & Seminars
Questions & Answers [09/01/2011] answer to question 2535: Gauze packs with internal chemical indicator
Discussion Forum
Publications [07/01/2011] new publication: Central Service Issue 6/2010
Education [07/01/2011] Recommendations by the Quality Task Group: [68] Problems today - tomorrow, how can we solve them?!
WFHSS Guidelines
WFHSS Training Programme
Industrial Partners
Commercial Announcements
Related Sites & Links
Humour [03/01/2011] new cartoon: Great Expectations for 2011
Industrial Partners:


Developed by Baumeister Mediasoft Engineering

WFHSS - World Forum for Hospital Sterile Supply

English | español


WFHSS - World Forum for Hospital Sterile Supply » Education » General » Sterilization Basics » Cleaning

The Sterile Supply Cycle: Cleaning

Author: Jan Huys


Cleaning of Equipment and Materials to be Sterilized

Sterilization of Medical Supplies by Steam, Volume 1 General Theory - Second Revised Edition
Sterilization of Medical Supplies by Steam, Volume 1 General Theory - Second Revised Edition
In a hospital or clinic it is necessary that all equipment and materials used for treating patients are absolutely safe for use: the chance for spreading of diseases should be kept as small as possible. Cleaning, decontamination and sterilization are important methods in this battle against this ever present threat. Especially since the fatal disease AIDS became so powerful and spread world wide, the demand for proper procedures for infection control gained momentum enormously. Diseases such as Hepatitis B, known to be transmitted through contaminated surgical instruments, stimulated the need for stricter guidelines for disinfection and sterilization.
This book focuses on the most common and most safe method used for sterilization in the Central Sterile Service Departments in healthcare institutions: sterilization by pressurised high temperature steam.
A first major step to improvement of sterile supply is the training of all personnel involved (technicians, staff and users). Moreover, in the recently published European standards on sterilization, education is required of everybody involved in sterilization, whether it concerns the manufacturer of the sterilizing equipment or the technician maintaining or using it. This series of books provides a foundation needed to fulfil this requirement. Originally intended to educate technical service personnel in remote health institutions, it has grown into a textbook that can be used by anyone interested in sterilization.

The International Federation for Sterile Supply (IFSS) and the World Forum for Hospital Sterile Supply (WFHSS) are pleased to recommend the book to all their members and all others involved in sterilization practices.

Click here for a book brochure/flyer in PDF format [494 KB].

This book is also available in Turkish:
Tibbi Malzemelerin Buharla Sterilizasyonu
Cilt I - Genel Teori

Edited by Hülya Erbil
Please contact Hülya Erbil for further information:
Author(s): Jan Huys
ISBN: 90-75829-04-3
Publisher: HEART Consultancy, Renkum, The Netherlands
Published: 2004
Pages: 295
Illustrations: more than 200 coloured illustrations, photos, graphs and tables
How to order: You can order the book through a bookshop using the ISBN number or directly from the author/publisher, Jan Huys/HEART Consultancy through letter, Fax, or Email:
  • Address: Jan Huys, HEART Consultancy, Quadenoord 2, 6871 NG Renkum, The Netherlands
  • Fax: +31-(0)317-450469
  • Email:
  • Web:





The Sterile Supply Cycle - Cleaning: Figure 1
Figure 1: Cleaning is essential: An instrument set as it comes back from the operating theatre...

Instruments and materials used during an operation will be covered with blood and remains of tissues; they may have been in touch with chemicals and fluids, dirt and dust. The tubing of hollow instruments may also will be full of these soils. In one way or the other, the items have to be reprocessed so that they can be safely used on another patient again. Cleaning plays an immensely important role in this process... A major requirement for equipment intended to be in touch with inner fluids of the body (the high risk areas) is that they should be sterile. However sterility (the absence of any viable organism) alone is not sufficient for safe use. An instrument, which is covered with sterile dirt or with remains of chemicals or corrosion, still is a serious health hazard. Thus all potentially dangerous soil or remains have to be removed. The health hazard caused by remaining soil (even when sterile) is only one of several reasons why goods to be sterilized, first have to be thoroughly cleaned before sterilization.

Any instruments or materials that are to be sterilized, should be cleaned.


Why cleaning of goods to be sterilized?

The Sterile Supply Cycle - Cleaning: Figure 2
Figure 2: Soiled instrument

1. Removal of all visible dirt, tissue, blood and foreign particles
Medical instruments, especially if they are going to be used in the high-risk areas of a patient, should have no viable micro organisms on them. However also any dirt and foreign particles (even sterile) left on instruments and materials can cause very dangerous complications if they happen to enter a patient through a wound. The body tends to reject any foreign matter that enters the body. A result may be the delay of recovery and of healing with a lot of extra suffering for the patient. It may be even extremely dangerous if during an operation such a dirt-particle would enter the blood stream.

The Sterile Supply Cycle - Cleaning: Figure 3
Figure 3: The vast majority of the bioburden should be removed by cleaning!

2. Reduction of the bioburden
By cleaning, the population of micro-organisms residing on the materials (known as the bioburden) is reduced considerably. In this way the initial contamination for a subsequent disinfection or sterilization is considerably lower and thus these processes will be more effective, as much less organisms have to be killed. Moreover, because all the visible dirt, including any left-overs of food, blood or pus, were removed, also the breeding ground has been taken away, preventing that any microorganisms that survived, have a chance to multiply. But there is another threat: The left-overs from dead microorganisms can cause feverish reactions if they enter the blood stream. The bits of the left-over dead bodies are referred to as pyrogens. There are microorganisms which contain poisonous chemicals which will be released when they are killed. Also these endotoxins may cause serious diseases. These are additional reasons to reduce the bioburden as much as possible before the killing action (disinfection or sterilization) is done.

By cleaning, the vast majority of the bioburden is removed. Thus
Cleaning is considered the most essential step in the sterile supply cycle

The Sterile Supply Cycle - Cleaning: Figure 4
Figure 4: Blood remains encrusted on instruments.

3. Protection of instruments against corrosion
Medical instruments are usually expensive precision instruments. Pivots and hinges are very sensitive to any left-over deposits of dirt. Small deposits of blood may easily develop into serious corrosion (rust). This corrosion is aggravated by the moisture and high temperatures during the processes used for sterilization, especially when steam is used. Corrosion may result in serious damage to the instruments and even render them useless or dangerous for the patient. Poor quality of water or incorrect dosing or cleaning agent may be a cause of corrosion. In an adequate cleaning process the chemistry of the cleaning agent, the quality of the water, the materials to be cleaned and the other process variables (temperature and time) are carefully considered, leading to the correct choice of chemicals and processes.

The Sterile Supply Cycle - Cleaning: Figure 5
Figure 5: After cleaning/disinfection equipment can be handled more safely

4. Ensure more safe movement of equipment and materials
After cleaning the instruments have to be inspected, sets are to be assembled and packed for sterilization. This requires intense handling. The cleaning and usually subsequent disinfection ensure that these activities can be performed more safely.

Summarizing the importance of cleaning of medical supplies:

  • removal of all visible dust and dirt
  • removal of breeding ground for surviving microorganisms
  • reducing of the bioburden
  • protection against corrosion
  • ensure more safe free movement of equipment and materials

The soils on used surgical instruments

After use in a medical procedure instruments and other materials will have attached to them a large quantity of blood and tissues. In addition there may be chemicals such as disinfectants, and other fluids. The majority of the soils however usually are the remains of tissues and blood; they contain proteins. When heating proteins above approx 50°C, they will start sticking together (like an egg becomes hard when boiling it). This sticking together is known as coagulation. In the hot water disinfection process or, subsequently during steam sterilization, the items are exposed to much higher temperatures and thus any, remaining protein residues will strongly attach themselves to the material. It therefore is essential that

  1. all these soils are removed before disinfection and/or sterilization
  2. the temperature of water, used for the pre-cleaning process is no more than 50°C.

Importance of quick cleaning after use

When organic soils such as blood, tissues, etc. are left to dry, they will adhere tightly to the underground and will as time passes, be more and more difficult to remove. (You experience this at home this when waiting a long time before cleaning the dishes after a meal). It therefore is essential that the materials are cleaned as soon as possible after their use. In some countries instrument sets are submerged in a disinfectant solution. This may solve the problem of drying up instruments, however these disinfectants also cause corrosion. Thus also in such case it is important to do the cleaning as soon as possible after use.

Cleaning procedure in the CSSD

After use, instrument sets usually arrive in their original trays in the cleaning section of the CSSD.

There are different opinions on the sequence of activities within the cleaning section. It will depend on the initial work done at the operating theatre and the way the materials are transported how instrument sets will arrive at the CSSD. When transporting is done dry as is practiced in many health facilities, the following sequence can be followed:

The Sterile Supply Cycle - Cleaning: Figure 6
Figure 6: Flushing with hand shower

1. Initial cleaning/flushing
Used instruments are covered with soils and dirt and will be contaminated. The instruments, in their tray, can be put in a deep basin and flushed with a hand shower at temperatures below 50°C. Ensure using a sufficiently deep basin to reduce splashes of water reaching the person performing the washing. Also initial cleaning can be done in a flusher and/or ultrasonic bath.

The Sterile Supply Cycle - Cleaning: Figure 7
Figure 7: Flushing with an automatic flusher or cleaning in an ultrasonic bath
The Sterile Supply Cycle - Cleaning: Figure 8
Figure 8: Sorting for manual cleaning and machine cleaning

2. Sorting for manual cleaning and machine cleaning
If not removed yet at the operating theatre, all disposable materials are to be taken out and instruments that cannot be washed by machine shall be separated from equipment that can be machine washed. This work requires great care, as here the chances of injuries is highest. Wearing an apron, gown and protective gloves is essential. Also wearing of a mask is recommended. See section: Personal Protection.

In order to prevent damage to instruments, it is recommended to take the instruments from their tray, into a second tray, and not "pouring" the instruments on the workbench, as this may damage the delicate instruments. In order to ensure that water sprays of the washer reach all surfaces of the instruments, it may be necessary to put large instrument sets in more then one tray.

The Sterile Supply Cycle - Cleaning: Figure 9
Figure 9: Manual cleaning

3. Cleaning/disinfection
By main cleaning all remaining soils are removed. Cleaning can be manual or by machine. In automatic washer disinfectors, first the load is washed, followed by a thermal disinfection by hot water. Usually manually pre-cleaned items, which allow machine washing, are still passing a machine washing cycle, rendering them disinfected.

The Sterile Supply Cycle - Cleaning: Figure 10
Figure 10: Unloading an automatic washer/disinfector
The Sterile Supply Cycle - Cleaning: Figure 11
Figure 11: Inspection

4. Verification of the cleaning and drying
After cleaning, all instruments are to be inspected for dryness and correct cleanliness. Special attention should be on the "difficult parts of the instruments such as the pivot, serrations, lumens etc. This check is usually done when also performing the functional check of the instruments. For more information see section: Performance testing and validation of cleaning process.

Note: In order to reduce risks for staff, in several countries the pre-cleaning of instruments, that have the capability of being placed directly into a washer-disinfector, is discouraged. In other words: whenever possible do machine cleaning only.

Cleaning: removing of all visible dirt, dust or other foreign material


The cleaning action

When washing your hands, you will rub them for some time while using warm water and soap. After washing you will rinse your hands, in order to remove the remaining dirt and soap. Any adequate cleaning process involves the cleaning factors of this simple hand washing procedure.

The Sterile Supply Cycle - Cleaning: Figure 12
Figure 12: Cleaning circle: all factors are essential

Water: the solvent: water is the carrier in which the soil is going to be dissolved or suspended and transported, away from the items to be washed. It provides the environment in which all cleaning actions take place

A mechanical action: such as wiping, brushing, spraying water under pressure, or ultrasonic waves in water.

A chemical action: detergent with water is used to soak and suspend the dirt and germs. Chemicals in the soil that cause deposits (e.g. limestone) may be dissolved. Cleaning agents may contain additional chemicals, which kill micro-organisms, dissolve proteins and protect instruments.

Heat improves the diluting power of the water and soap or detergent

A minimum time is needed for objects to be subjected to the actions in order to be effective. The time required for adequate cleaning will depend on the methods and intensity of the other actions.

Note: in order to prevent coagulation of tissues and blood, the temperature for pre-cleaning or neutral detergents should be limited to below approx 50°C. Alkaline detergents however, strongly depend on higher temperatures in order to hydrolyse (break down by means of water) protein residues. Therefore the temperature for the main cleaning needs to be the right one for the type of detergent.

The cleaning circle

The total cleaning action resulting in a clean product can be presented by a circle, with each factor indicating the relative contribution to the total cleaning action (cleaning circle according to Sinner). Depending on the method of cleaning that is used, the share of the individual cleaning factors will differ. Whereas in a manual cleaning process using a brush, the mechanical action contributes to a large extent to the cleaning result, in machine cleaning, the only mechanical action available is the flushing of the water. Thus in order to result in a similar cleanliness, the more of the other factors such as the chemistry and temperature will be needed.

The Sterile Supply Cycle - Cleaning: Manual cleaning or ultrasonic cleaning: The vast majority of the cleaning action is caused by the mechanical action. The Sterile Supply Cyle - Cleaning: Machine cleaning: A large share of the cleaning action is now taken over by chemistry, temperature and time.
Manual cleaning or ultrasonic cleaning: The vast majority of the cleaning action is caused by the mechanical action. Machine cleaning: A large share of the cleaning action is now taken over by chemistry, temperature and time.
Figure 13: Comparing the contributions of the factors involved in manual cleaning and machine cleaning.


Principles of the chemistry of cleaning

In the cleaning process, all soil is to be removed from the goods to be cleaned. This can be done by dissolving, or, when this is not possible, by breaking it up and bringing it into the water (bringing in suspension). Being in the water it then can be flushed away during the rinsing. Soils on medical equipment after surgical procedures will contain blood, tissues, fats and oils and all kind of chemicals. All these have to be removed. Water plays an essential role in the cleaning process. Soils, like fats cannot be diluted in water and are to be treated such that they will be suspended in water. Proteins, much larger then the fats also are not soluble in water, and should be broken down first into smaller particles that can than can be removed more easily. It is clear that understanding of cleaning requires in-depth understanding of the chemistry of cleaning: a dazzling complicated process of interactions of the objects to be cleaned, the soil, the cleaning agents and water. A whole industry has developed, producing sophisticated products for the cleaning of the wide range of materials. Detailed information is available in various publications and websites. For a basic understanding the chemistry of cleaning, this section takes a closer look at the ingredients involved in the cleaning process: the water and chemicals and how they are aided by mechanical action and temperature of the solution.

Water and cleaning

Water is an amazing fluid with fascinating properties. It is available abundantly; it is essential for all living beings. It is used in incredibly many ways in society, household and industry. It also plays a key role in the cleaning.

The Sterile Supply Cycle - Cleaning: Figure 14
Figure 14: Chemical structure and polarity of the water molecule

The Sterile Supply Cycle - Cleaning: Figure 15
Figure 15: Hydrogen bond: Bond of neighbouring water molecules

Water structure and water properties
The chemical formula for water is H2O. The formula indicates that a molecule (the smallest particle of a substance) of water it is built up of 2 atoms of Hydrogen (H) and a single atom of Oxygen (O). Through the interactions of electrons circling around the nuclei of Hydrogen and Oxygen the molecule is kept together. The electrons are negatively charged. The nuclei are positively charged. In a water molecule, the outer negative electrons tend to spend more time around the Oxygen nucleus then around the Hydrogen nucleus. This causes the molecule as a whole to be charged negatively at the Oxygen side and positively charged at the Hydrogen side: the water molecule is said to be polar. This polarity causes neighbouring water molecules to be attracted to each other. This so called Hydrogen bond is the cause of a number of fascinating properties of water, that it makes it so special.

  • It is a good solvent for a large number of substances
  • It has a relative high boiling point
  • It is stable
  • It has a very high surface tension

These properties also affect the behaviour of water in the cleaning process.

Problems related to cleaning with water

For adequate cleaning it is essential that soils are dissolved or somehow suspended into water allowing the soils to be flushed away. Water can dissolve many substances, however, unfortunately it has a number of properties that makes it not directly suitable for removing a number of soils such as the oils, fats and proteins. These however are the very substances so much present on used surgical instruments and materials! Somehow this problem has to be solved.

The Sterile Supply Cycle - Cleaning: Figure 16
Figure 16: Pure water beads up due to surface tension of the water, thus inhibiting the cleaning process.

Water prevents wetting of surfaces: surface tension
For cleaning it is essential that water can dissolve and bring in suspension all kind of soils. In order to do that, it is important that water gets in touch with the soils that it should dissolve. In practice, normal pure water does not like to wet surfaces, it tends to bead-up! Inside the water, each molecule is surrounded and attracted by other water molecules due to the dipole nature of the water molecules. However, at the surface, those molecules are surrounded by other water molecules only on the water side. A tension is created as the water molecules at the surface are pulled into the body of the water. This tension causes water to bead-up on surfaces (glass, fabric). The drop will hold its shape and will not spread: the beading-up of water prevents the wetting of the surface and thus inhibits the cleaning process.

The Sterile Supply Cycle - Cleaning: Figure 17
Figure 17: Vegetable oil floats on water. The oil will not dissolve in the water.

Water cannot dissolve fats and oils
By its polar nature water can dissolve a great number of substances: Generally it can be said that substances with a polar structure like water itself, can be dissolved in water. These are substances such as many salts, acids, bases etc. They are known to be hydrophilic (water-loving). However an important group of soils is not polar by nature and thus cannot be dissolved in water. These substances are said to be hydrophobic (afraid of water). Among them are fats, oils and proteins. These however are all substances, which are found abundantly on used surgical instruments! Thus water alone cannot do our cleaning job properly. For adequate cleaning it is essential that also these soils can be removed.

The Sterile Supply Cycle - Cleaning: Figure 18
Figure 18: Surfactants in soapy water cause the water to spread and adhere to the surface

The Sterile Supply Cycle - Cleaning: Figure 19
Figure 19: Symbolic presentation of a surfactant molecule

Improving cleaning capability of water: Surfactants (tensides)
A first requirement is to make sure that the water will want to get in touch with the surface it touches. This means that the surface tension should be reduced. By adding a chemical that reduces the surface tension, the water can spread and wet surfaces. Chemicals that are able to do this effectively are called surface-active agents, or surfactants. Also the term tensides is used. Surfactants are substances with molecules that on one end tend to be attracted to water (the hydrophilic end) and on the other end tend to attach to fatty substances (which is repelled by water: the hydrophobic end). These substances are said to make water "wetter." Surfactants also are able to dissolve the fats and oils: they loosen them and emulsify (disperse) them into the water. Also they ensure that they keep the soils in suspension so that they can be flushed away with the water. Common surfactants are soaps and detergents.

Also other substances such as phosphates can emulsify fats and oils, and are used in detergents. They however do not cause considerable reduction of the surface tension.

The Sterile Supply Cycle - Cleaning: Fig. 20a - Object with a soil layer The Sterile Supply Cycle - Cleaning: Fig. 20b - The soil is pulled into suspension by the surfactant The Sterile Supply Cycle - Cleaning: Fig. 20c - All soil is suspended in the water The Sterile Supply Cycle - Cleaning: Fig. 20d - The water with the soil is flushed away. The object is clean.
Object with a soil layer The soil is pulled into suspension by the surfactant All soil is suspended in the water The water with the soil is flushed away. The object is clean.
Figure 20: Removing of soil with water to which a surfactant was added. Removal can be aided by a mechanical action such as brushing and flushing.

Composition of water: water quality

The Sterile Supply Cycle - Cleaning: Figure 21
Figure 21: Water with ions of split-up minerals, acids and bases dissolved in it

By nature, water contains a wide range of substances. It may contain dust and dirt particles, micro-organisms and minerals. Minerals are chemicals found in nature, such as cooking salt (NaCl), Gypsum (CaSO4), Calcium bicarbonate (CaHCO3) and many others. When diluted in water, these minerals usually are split up ions, which are charged particles. The split-up results in positively charged ions: the cations (attracted by a cathode, the name of a negative electrode), mainly Hydrogen and metal ions (K, Na, Ca, Fe, etc.) and negatively charged ions, the anions (attracted by the anode: a positive electrode). Anions are usually left-overs of acids and salts). The concentration of these ions in water very much depends on the geological structure of the site where the water is coming from. In areas with lots of calcium (lime) and magnesium, the water will contain ions of these metals.

The Sterile Supply Cycle - Cleaning: Fig. 22 - Deposits of scale near the outlet of a tap and on a heating element due to hard water The Sterile Supply Cycle - Cleaning: Fig. 22 - Deposits of scale near the outlet of a tap and on a heating element due to hard water
Figure 22: Deposits of scale near the outlet of a tap and on a heating element due to hard water

Hard and soft water
When water contains high amounts of certain salts of calcium and magnesium (the bicarbonates) it is known as "hard" water. At higher temperatures these salts are not soluble in water and tend to form a hard scale on surfaces covered with such water. This causes discoloration of instruments and can cause damage to the cleaning equipment. That is why these minerals have be removed or modified to salts which remain in solution and flushed away with the water. This can be done by additives in the cleaning agent. Another method, which is even better, is by removing these minerals from the water before it is used for cleaning. This is known as water softening: a process where the insolvable calcium and manganese salts are replaced by a solvable sodium salt. The sodium salt remains in the water solution; it thus does not cause deposits.

The Sterile Supply Cycle - Cleaning: Fig. 23 (L) - Pitting caused by chlorine (L). The Sterile Supply Cycle - Cleaning: Fig. 23 (R) - A surgical instrument put in salty water.
Figure 23: Pitting caused by chlorine (L). A surgical instrument put in salty water (R).

Piped water may contain chlorides, or chlorides are coming into the water with the soils during the cleaning phase. Bodily fluids usually contain physiological salt, which naturally contains chlorine. Chloride ions are very reactive and easily pull the iron molecules of the steel into the water solution. Thus chlorine that is dissolved in water can cause serious corrosion of any metal instruments and is clearly visible by holes in the steel, known as "Chloride induced pitting". It is essential that any chloride will be removed during the last phase of the cleaning process.

The longer-term effect of chloride on corrosion can easily be demonstrated by submersing an instrument in salty water. Within a few hours, even the best, high quality stainless steel instrument will already start corroding. After a day a brownish cloud of rust will have formed. This is known as "bleeding" of the instrument.

The Sterile Supply Cycle - Cleaning: Fig. 24 - In pure water 1 in 10.000.000 molecules one of the H nuclei moves to another water molecule. The electron of the H atom is left in the donating ion causing the donor to be negative and the receptor to be positively charged. The result is a H3O+ and OH- ion.
Figure 24: In pure water 1 in 10.000.000 molecules one of the H nuclei moves to another water molecule. The electron of the H atom is left in the donating ion causing the donor to be negative and the receptor to be positively charged. The result is a H3O+ and OH- ion.

Acidity of water: pH
In pure water the vast majority of water molecules stay together. However in a rare case, due to the hydrogen bond, the nucleus of a Hydrogen atom (a proton) of one molecule jumps to that of a neighbouring molecule. This will then have 3 hydrogen atoms attached to it and will become a positively charged H3O+ ion. The other water molecule, which has lost the hydrogen nucleus, but kept its electron, becomes a negatively charged OH- ion. In pure water this happens about 1 in 10.000.000 (107) molecules. In pure water both the amount of H3O+ and OH- are equal and its acidity, also indicated as pH, is 7 (the number of zero's of the concentration) and is said to be neutral. It is found out that when the concentration of H3O+ becomes higher then the OH- the solution becomes acid (for example 1 in 10.000 molecules or 104). The pH will be less then 7. In the example the pH is 4. If the number of H+ becomes lower then the number of OH- the solution becomes basic. This acidity of water has great influence on the cleaning properties of the chemicals used for cleaning and affects the corrosion caused by chemicals and the water.

The Sterile Supply Cycle - Cleaning: Fig. 25 - A surplus of H3O+ (or what is the same the H+) causes acidity. A surplus of OH- causes a fluid to be basic. Acids typically add H+ cause and increase of acidity/thus a lower Ph. Bases bring in OH- ions and cause a fluid to basic, increasing the pH.
Figure 25: A surplus of H3O+ (or what is the same the H+) causes acidity. A surplus of OH- causes a fluid to be basic. Acids typically add H+ cause and increase of acidity/thus a lower Ph. Bases bring in OH- ions and cause a fluid to basic, increasing the pH.
The Sterile Supply Cycle - Cleaning: Figure 26
Figure 26: Opaque and dark blue discoloured instruments due to silicates

In locations where the tap water is taken from sandy locations, water contains silicates: they are minerals with silicon in it (the main component of sand). Silicates are salts that tend to deposit on instruments causing opaque (at the beginning), or dark blue layers (when growing thicker). By adequate water treatment (de-ionized water) where the vast majority of minerals including the silicates are removed, this problem can be solved. Also cleaning agents may have chemicals, which help to keep silicates in solution and thus prevent silicon salt deposits.

Improving water quality

The water quality has a great influence on the result of the cleaning process. Water analysis and water treatment are issues, which require specialist know-how. For planning your water treatment installation and solving problems related to water seek advice from organizations or companies with thorough experience and know-how. Here only a brief introduction on water treatment can be presented. Depending on the stage of the cleaning process a more or less high quality of water is required. High quality in this context means, water with a minimum of particles and minerals dissolved. The initial rinse may be normal piped drinking water. However the water for the final rinse should have a higher quality with a minimum of minerals dissolved in it. For improving the water quality used for the activities in the CSSD several methods are used.

The Sterile Supply Cycle - Cleaning: Figure 27
Figure 27: Water filter cartridges
The Sterile Supply Cycle - Cleaning: Figure 28
Figure 28: Large capacity water pre-filter

Filtering: In order to remove major particles of dust and dirt floating in water, it is passed through a sieve or filter element or filter bed that catches small particles. The tighter the mesh of the sieve, the smaller the particles must be to pass through. Filtering is not sufficient to completely purify water, but it is often a necessary first step, since such particles can interfere with the more thorough purification methods or would clog-up these systems very quickly making them extremely expensive to be operated. Therefore usually a prefilter system is installed.

The Sterile Supply Cycle - Cleaning: Figure 29
Figure 29: Typical water distilling plants, for small water quantities

Distilling: Distillation involves boiling the water to produce water vapour. The water vapour then rises to a cooled surface where it can condense back into a liquid and be collected. Because the solutes are not normally vaporized, they remain in the boiling solution. However distillation does not completely purify water, because of contaminants with similar boiling points and droplets of un vaporized liquid can be carried with the steam. Still, 99.9% pure water can be obtained by distillation. Distilling results in high-quality water; however an enormous amount of energy is required for this process. In situations where large quantities of high-quality water is needed (as for the washing process and steam sterilization in the CSSD), other methods, such as water softening, de-ionizing and reverse osmosis are used.

The Sterile Supply Cycle - Cleaning: Figure 30
Figure 30: Water softener for continuous use (double unit). The white vessel contains salt, used for regeneration of the resin.

Water softening by ion-exchanging

The salts causing the water hardness, such as Calcium bicarbonate (CaHCO3) and Magnesium Chloride (MgCl2) and tend to deposit, are exchanged with salts of Sodium. These Sodium salts are dissolved very well in water, and thus are not deposited. In a water softener, the hardness ions are exchanged with the Sodium ions. This can be done by passing the water through a charged resin column that has side chains that trap calcium, magnesium, and other heavy metal ions and replaces them by Sodium ions. The sodium salts are soluble in water and thus will not cause any deposits. In stead of resins also zeolites are used.

When saturated with hardness ions, the resin can be regenerated with sodium ions by flushing with salty water (brine) and the resin can be used again for water softening.

The Sterile Supply Cycle - Cleaning: Figure 31
Figure 31: A two-step ion-exchanger for demi-water production

De-ionization by two-step ion-exchanging

In this process, all ions in the water solution are removed in a two-step process. In the first stage the metal ions (the positively charged cations) are exchanged by H+ ions. In a second stage also the remains of the acids and salts, (the negatively charged anions), are exchanged by OH- Ions. The H+ and OH+ together form H2O: water. In this way all minerals are removed.

In many laboratories, this method of purification has replaced distillation, as it provides more quickly a high volume of very pure water. Also water for the final rinse in the cleaning process usually is treated this way. Water purified in this way is called de-ionized water, demineralized water or demi water.

Due to their very weak bonding with the resins, silicates, causing an opaque or bluish layer on stainless steel instruments, may pass through ion-exchangers, especially after the resins are getting close to saturated. Due to the fact that silicates do not increase the conductivity of the water, the presence of silicates may be overlooked easily.

The Sterile Supply Cycle - Cleaning: Figure 32
Figure 32: Reverse-osmosis unit

Reverse osmosis: also known as hyperfiltration. Mechanical pressure is applied to the impure solution which is forced through a semi-permeable membrane. When the pore size of the membrane is approx 0.0005 micron (compare to bacteria, which are 0,2-1 micron). The term is reverse osmosis, because normal osmosis would result in pure water moving in the other direction to dilute the impurities. Reverse osmosis is theoretically the most thorough method of large-scale water purification available. As the membrane is very sensitive to damage by Chlorine, metal ions and other impurities, usually water filters and water softening systems are used in combination with the Reverse Osmosis unit.


Chemicals used in the cleaning process

For the total cleaning process one or more chemicals are used. In manual cleaning usually a single detergent is sufficient. However in machine washing, a number of chemicals are used, which are applied in the individual steps of the cleaning/disinfection process. Chemicals used for cleaning are the result of advanced research, and provide adequate cleaning action for the target soils and processes they are designed for. Recently the environmental impact and safety in relation to chemical products came more and more important and resulted in new, more environmentally-friendly products.

Automatic washer/disinfectors are equipped with dosing systems, which can be programmed to inject the required amount of each individual chemical at the right moment in the process.

Your supplier can advise you about which products are most suitable for your specific situation. This section briefly describes the most important products used in the cleaning/disinfection process.

Detergents/cleaning agents

The Sterile Supply Cycle - Cleaning: Figure 33
Figure 33: Cleaning agent and rinse aid for automatic washer disinfectors.

These products are the main chemicals used in the cleaning process. They may contain surfactants, alkali, enzymes, corrosion inhibitors, solvents etc. For the cleaning of surgical instruments, dedicated cleaning agents have been developed with the typical soils found on used instruments in mind. Products are available for manual cleaning and automatic washer disinfectors. Also for delicate instruments such as flexible endoscopes dedicated products are available.

Detergents have the following main ingredients:

Surfactants: soap and detergents

Surfactants are an important component of a cleaning agent; they decrease the surface tension of the water and enable the suspension of fats and oils into water (see also Improving cleaning capability of water: Surfactants (tensides). Soap and detergents are surfactants. Soap is based on fats of animals and plants whereas detergents are synthetic petrochemical substances. Detergents can be engineered for specific purposes. A wide range of surfactants are available and are used depending on their application. They are divided in 3 major groups. Depending on the charge of the active part of the surfactant, they are known as Cationic, Anionic and Neutral or Non-ionic. For detailed information refer to relevant documentation/websites.


Alkali are substances which in a water react alkalic (they bring OH- ions in the detergent solution). They are substances such as Ammonia (NH3), Soda (Na2CO3), Phosphates, Silicates and Hydroxides (Sodium hydroxide: NaOH) and Potassium hydroxide (KOH). The alkali have a number of functions:

  • They ensure optimized activity of the surfactants.
  • The alkalic solutions are used for removing fats and oils. When fats and oils are reacting with a base they change into fatty acids and glycerine, which all are water soluble. The fatty acids themselves even are tensides and thus stimulate emulsification of the fats. This process is known as saponification. In this way fatty substances are relatively easily removed.
  • Also some alkali (e.g. phosphates) can bind hardness ions (Ca2+ and Mg2+), which are in the water or soils.


These are chemicals, which bind the hardness ions: Calcium and Manganese. By binding them they prevent deposits of hardness scale. Examples are Phosphates, Phosphanates. A major problem of the phosphates has been the dramatic increase of algae growth in surface water, in quantities that they could not be broken down rapidly enough. That is why recently the use of phosphates is discouraged and new substances were looked after, which are more environmentally friendly. Substances known as Zeolites now have become in use as builders. They exchange sodium ions with the hardness ions. The quantities/formulation for builders will depend very much on the water quality used for the washing. Surgical instruments usually cleaned in washer disinfectors, using de-ionized or demineralised water. That is why detergents for machine-washing of surgical instruments usually have hardly any builders included. Builders are used in common cleaning agents intended to be used with normal tap-water: dishwashing, laundry etc.

Corrosion inhibitors

Stainless steel is hardly affected by the detergent solutions. However aluminium is sensitive for the alkalic solutions of detergents. That is why, for the protection of aluminium materials, corrosion inhibiters are added. Usually they are Aluminium silicates. These chemicals cause a protective oxide layer on the aluminium.


These are chemicals which kill (micro-) organisms such as bacteria, fungi, viruses. Usually these chemicals kill organisms by oxidation of the proteins of the living cell. Examples of biocides are hydrogen peroxide, peracetic acid, sodium hypochlorite and certain ammonium compounds.

In the cleaning process of medical equipment, the inactivation of organisms is usually done by high temperature of water (thermal disinfection). However anesthetic materials are often disinfected at 65°C with the use of a chemical disinfectant.


The Sterile Supply Cycle - Cleaning: Figure 34
Figure 34: Enzyme breaking down a large protein into smaller sections, which can be dissolved in water. The enzyme locks in (like a key in a lock) on weaker parts of the protein and cuts it at those positions. The enzyme itself is not affected and can perform many cuts

An enzyme is, in biology, a special protein molecule whose function is to facilitate or otherwise accelerate most chemical reactions in cells. They are biological catalysts. That can break down large molecules such as proteins, fats and starch to smaller pieces, which then can be diluted in water. In this way stains caused by blood and fats can be removed. For breaking down each group of biological substances there are different, specific enzymes. For example proteases break down proteins; Lipases break down fats (lipids). In the process of breaking down these large molecules, the enzyme itself is not used up. When given sufficient time very small quantities can break down large amounts of proteins. As the soils of used surgical instruments contain much of the organic soils, cleaning agents for this purpose, may also contain enzymes.


Neutralisers are used when the main cleaning action is done with an alkalic cleaning agent. In order to prevent that the alkalic residues may affect the materials to be washed, the alkality is reduced by applying an acid in the water during a neutralizing phase. Usually the acids are weak acids such as citric acid. Also phosphoric acid is used. Neutralizers are only necessary when alkaline cleaning agent was used.

The Sterile Supply Cycle - Cleaning: Figure 35
Figure 35: Damage to the steel surface due to friction. Lubricants create a layer, which prevent damage to the steel surface.


Surgical instruments are prone to corrosion, especially at the steel surfaces in the hinges. By nature, stainless steel has a protective layer, of Chromium oxide, which becomes thicker with time. Due to friction, the protective surface of the steel is damaged. At these places the bare iron will be exposed and the steel will easily be corroded. Also mineral left-overs (residues) in the hinges stimulate corrosion. That is why lubricants are added to the rinsing water, which form a protective layer on the steel. Lubricants are usually paraffin oils.

The Sterile Supply Cycle - Cleaning: Figure 36
Figure 36: Instruments with water droplets due to surface tension. A rinse aid will cause the droplets to spread over the steel surface.

Rinse aids

After disinfection with hot water, the load is to be dried. As seen before, water has a high surface tension, and water tends to bead up on the surface of the materials. These drops only evaporate very slowly and thus results in a long drying time. That is why in the water used for the final rinse a rinse aid can be added. It contains a surfactant, which causes the spreading of the water on the surface. Due to the increased surface, the water will evaporate more quickly and the drying time can be reduced considerably. In this way the energy consumption of the total process is also reduced considerably.


Importance of intermediate rinsing after cleaning

After the cleaning process has taken place, chemicals may be left on the instruments and materials. When not rinsed properly or when water of poor quality is used for rinsing (with many minerals in it). these chemicals may be left on the surface. These left-overs, they can cause serious damage to the instruments, during drying and especially when subsequent sterilization in steam, where the moist environment can easily cause corrosion. That is why it is essential that after cleaning, the load is rinsed thoroughly. Preferably, rinsing is done with high quality water: e.g. water prepared by de-ionization or Reverse Osmosis.


Disinfection and drying

In most washer disinfectors, as the name already indicates, the intermediate rinsing will be followed by a disinfection phase, by rinsing with hot water, usually approximately at 90°C for 1 minutes; 80°C for 10 min or 70°C for 100min (EN15833).

In this way, materials for which disinfection is sufficient then are ready for use; others will be sufficiently safe for subsequent handling in the CSSD where they are prepared for sterilization.


Cleaning methods in the Central Sterilization Department

Depending on materials to be cleaned and resources available cleaning will be done in different ways. Some materials can be washed in automatic washer/disinfectors. Others can only by cleaned by hand. In many cases a combination of manual and machine washing will be used.

Manual Cleaning

In order to reduce risk, any cleaning that can be done by machine is done so. As manual cleaning is the most risky task within CSSD, whenever possible, cleaning is done by machines. Manual cleaning is done when machine cleaning is not possible.

The Sterile Supply Cycle - Cleaning: Figure 37
Figure 37: Manual Cleaning

Manual cleaning can be done using a range of cleaning aids:

The Sterile Supply Cycle - Cleaning: Figure 38
Figure 38: Brushes in all shapes and sizes

Brushes: external and internal

A wide range of brushes is available for manual cleaning, suitable for individual cleaning tasks.

External brushes: for cleaning the outside surfaces of objects. They may have hard or soft hairs.

Internal brushes: for cleaning of hollow instruments. A range of diameters and lengths is available for any type/size of hollow instruments and materials.

Do not use steel brushes for cleaning, as they damage the protective layer on stainless steel and aluminium instruments!

The Sterile Supply Cycle - Cleaning: Figure 39
Figure 39: Sponge or towel

Sponge or towel

Delicate instruments such as optics may be cleaned by soft towel or sponge.

The Sterile Supply Cycle - Cleaning: Figure 40
Figure 40: Spray gun

Spray gun

A spray gun is essential for rinsing/flushing of hollow instruments. Various nozzles are available for a range of specific cleaning applications.

The Sterile Supply Cycle - Cleaning: Figure 41
Figure 41: Hand shower

Hand shower

The hand shower can be used for an initial rinse of instruments.

Use a deep basin, which will help to prevent splashing sideways. Make sure that the water pressure is not too high in order to limit splashing. Only use cold water for blood removal! Protect yourself by wearing gloves and mask, or use a splash screen. See section personal protection


The Sterile Supply Cycle - Cleaning: Figure 42
Figure 42: Instrument flusher

Instrument flusher

In a flusher, instrument sets are submerged and spayed by powerful jets of water. The majority of dirt and soils are flushed away. Instruments of which not all soil is removed, either are cleaned additionally in an ultrasonic cleaner or are manually cleaned. Subsequently usually they are washed/ disinfected in a washer/disinfector.

Ultrasonic cleaning: the microscopic "brush"

For adequate cleaning the mechanical action is essential, in order to break up the soil-layer and thus to allow the cleaning agent to penetrate the soiled surface, break it down in smaller particles and take the contaminants into suspension. Normal cleaning by brushes, flushing etc. will not be able to reach all surfaces. By ultrasound, the water is shaken at speeds above sound. It is like brushing at a speed higher than the vibrations of sound. It has the advantage that the cleaning action can take place at any location in or on an instrument where water can reach.

Principle of ultrasonic cleaning

The Sterile Supply Cycle - Cleaning: Figure 43
Figure 43: The water/steam curve: when at a given temperature the pressure on the water decreases beyond the curve, the water will evaporate.

The Sterile Supply Cycle - Cleaning: Figure 44
Figure 44: Ultrasonic waves with areas of increase and decrease of pressure

Basics: Water cavitation

At a given temperature water can exist only in the liquid state above a minimum pressure. When the pressure decreases below the critical pressure, the water will become a gas. For example: When the water is 60°C, at atmospheric pressure (0 Bar on the pressure scale) that water is fluid. If the pressure is reduced to below of -.8 Bar the water cannot exist as fluid anymore and will evaporate. In an ultrasonic cleaner, water is vibrated at ultrasonic frequencies. These ultrasonic waves cause very fast pressure decreases and increases in the fluid. The sudden decrease causes moments that water cannot exist in the fluid state anymore and gas bubbles will form. At the subsequent increase of the pressure the bubbles will collapse again. This process of the creation of minuscule bubbles or cavities in the water, is known as cavitation.

The Sterile Supply Cycle - Cleaning: Figure 45
Figure 45: Due to quick pressure reduction in the water, cavities are formed in the water, which collapse as pressure rises.

Microscopic brush: Caused by cavitation

Ultrasonic cleaning depends upon this process of cavitation, the rapid formation and violent collapse of minute bubbles or cavities in a cleaning liquid. This agitation by countless small and intense imploding bubbles creates a highly effective scrubbing of both exposed and hidden surfaces of parts immersed in the cleaning solution. As the frequency increases, the number of these cavities also increases but the energy released by each cavity decreases making higher frequencies ideal for small particle removal without damage of the items to be cleaned.

The Sterile Supply Cycle - Cleaning: Figure 46
Figure 46: Main components of ultrasonic cleaner

Components of an Ultrasonic cleaner

1. Ultrasonic generator

Through the mains electricity supply the electric waves at ultrasonic frequencies are created. (depending on the application 25kHz-50kHz).

2. Transducers
One or more transducers (vibrating elements) transform the electric waves into ultrasonic sound waves.

3. Cleaning tank
The cleaning tank contains the cleaning fluid (usually water with an enzymatic detergent). At the bottom of the cleaning bath the transducers are attached.


Ultrasonic treatment can be very well used for stainless steel instruments. Especially for instruments sensitive to mechanical impact: microsurgical instruments; dental instruments.

Do NOT use ultrasonic cleaning for

Flexible endoscopes. They should NEVER be treated in ultrasonic bath

Elastic materials. They absorb the ultrasonic waves and will weaken the cavitation to occur and thus there will be a less effective cleaning action. Therefore elastic materials such as rubber ware and materials of silicone should not be put in an ultrasonic cleaner.

Of MIS instruments or rigid endoscopes only those components can be cleaned by ultrasound that the manufacturer approves in its instructions. Usually optical systems should NOT be cleaned in an ultrasonic bath.

Ultrasonic cleaning equipment

Ultrasonic cleaners are available as smaller table top units and large basins integrated in working tables, sinks etc. They can be suitable for taking one or more standard instrument trays. Ultrasonic cleaning units may also be integrated in automatic washer disinfectors (takt machines).

An unprotected ultrasonic bath causes an irritating high-pitch sound. Moreover at the surfaces aerosols may form. That is why an ultrasonic bath should have an adequate lid. Larger Ultrasonic baths are equipped with a mechanism, which lifts out the content when opening the lid.

The Sterile Supply Cycle - Cleaning: Figure 47
Figure 47: Desktop ultrasonic cleaners
The Sterile Supply Cycle - Cleaning: Figure 48
Figure 48: Ultrasonic cleaning basin, integrated in a work bench
The Sterile Supply Cycle - Cleaning: Figure 49
Figure 49: Ultrasonic cleaner with lifting system for trays; with lid, reducing noise

Guidelines for ultrasonic cleaning

  • In order to prevent ear irritation the unit should be equipped with a lid.
  • Fill bath according to instructions of the manufacturer.
  • Use a cleaning agent or combined cleaning/disinfection agent in concentrations and temperatures as recommended by the manufacturer.
  • Make sure the bath is degassed. Any gases in water reduces the cavitation and thus the cleaning effect. Therefore use warm water, preferably upto 40°C. This will stimulate degassing, thus improving the cleaning results. It however should not be above 60°C to prevent coagulation; or, it is necessary to add a suitable detergent that will prevent protein coagulation.
  • Make sure that all items to be treated are fully immersed.
  • Hinged instruments should be opened.
  • Do not overload trays.
  • Renew the ultrasonic bath at least twice a day. If necessary more frequently, depending on the conditions of use.

Testing performance of ultrasonic cleaners

There are two simple tests for checking the performance of your ultrasonic cleaner:

a. Glass slide test

Wet the frosted portion of a glass slide with tap water and draw an "X" with a No. 2 pencil from corner to corner of the frosted area. Making sure that the tank is filled to the fill line, immerse the frosted end of the slide into fresh cleaning solution. Turn on the ultrasonics. The lead "X" will begin to be removed almost immediately, and all lead should be removed within ten seconds.

b. Aluminium foil test

Several tests using aluminium foil have been described. You can use the following procedure: Cut three small pieces of aluminium foil about 10cm x 20cm each. Fold each piece over a rod that you will use to suspend the foil in the tank. A clothes hanger works well. Your cleaner should be filled with an ultrasonic cleaning solution, degassed, and brought up to normal operating temperature. Suspend the first "square" in the center of the tank and the other two a couple of inches from each end of the tank. Make sure that the tank is filled to the fill line, and turn on the ultrasonics for about ten minutes. Remove the foil and inspect: All three pieces of aluminium foil should be perforated and wrinkled to about the same degree. Another test recommends the use of 9 strips of aluminium foil, 15mm to 20 mm wide, suspended within 10 mm of the bottom of the tank, but not touching it. Other tests recommend the use of 9 strips of aluminium foil 15mm to 20 mm wide suspended within 10 mm of the bottom of the tank, but not touching.

The Sterile Supply Cycle - Cleaning: Fig. 50 - Aluminium foil tape for testing ultrasonic cleaners. You can also use house hold aluminium foil! The Sterile Supply Cycle - Cleaning: Fig. 51 - Foil after inadequate cavitation (magnification 10 x). No perforations! The Sterile Supply Cycle - Cleaning: Fig. 52 - Adequate cavitation: The foil is perforated (magnification 10x)
Figure 50: Aluminium foil tape for testing ultrasonic cleaners. You can also use house hold aluminium foil! Figure 51: Foil after inadequate cavitation (magnification 10 x). No perforations! Figure 52: Adequate cavitation: The foil is perforated (magnification 10x)

c. Chemical indicators for checking cavitation

The Sterile Supply Cycle - Cleaning: Fig. 53 - The vial with the cavitation indicator (measuring about 1cm diameter, and 2 cm high). It contains glass beads and a chemical, which initially is green. When exposed to an adequate ultrasonic cleaning cycle, its colour will change from green to yellow within several seconds.
Before - After

Figure 53: The vial with the cavitation indicator (measuring about 1cm diameter, and 2 cm high). It contains glass beads and a chemical, which initially is green. When exposed to an adequate ultrasonic cleaning cycle, its colour will change from green to yellow within several seconds.

Recently also chemical indicators appeared on the market, which can be used for checking the correct operation of an ultrasonic bath. It actually verifies the cavitation capability of the ultrasonic bath. The cavitation triggers a chemical reaction in the test fluid, causing a clear colour change. The test device is a closed vial/capsule containing the fluid with glass beads in it. The vial is put in the ultrasonic bath, which is switched on at specified frequency, time and temperature. When an effective cavitation is reached, the colour of the fluid in the vial changes from green to yellow. Advantage of this system is that it can be used together with the load to be cleaned.

Cleaning with automatic washer/disinfectors

As the name indicates a washer/disinfector runs a washing cycle, followed by a disinfection phase. Disinfection is performed by flushing with hot water of approximately 90°C for 1-10 minutes. The machine renders equipment clean, disinfected and dry: ready/safe for further handling, required for inspection and packaging. The machines are fast and are easy to operate. They usually have programmes for different types of loads. Within the European Community new washer disinfectors should meet the European Standard EN13886.

Typical cleaning/disinfection process in an automatic washer disinfector

The following diagram shows the phases of a typical cleaning process in a washer disinfector. Details may differ for various manufacturers and individual models.

The Sterile Supply Cycle - Cleaning: Figure 54
Figure 54: Typical cleaning process for an automatic washer/disinfector

Pre rinse: Initial rinsing of the load with cold water. A major part of the soils are flushed away. The temperature should not exceed 35°C.

Cleaning: The detergent is added and the water is heated up to approx. 45-55°C. The major cleaning takes place during this phase. Note: For alkalic cleaning agents, higher temperatures may be used.

Neutralisation. When an alkalic cleaning agent was used, the water is chemically neutralized in order to prevent corrosion.

Intermediate Rinse. All remaining soils are carefully washed away with cold fresh water.

Disinfection at 90-95°C for approx 1-10 minutes. A rinse-aid containing a surfactant may be added which will reduce the drying time. Time and temperature will depend on the load.

Drying. In order to prevent recontamination it is essential that the load is dry by the time it is removed.

The Sterile Supply Cycle - Cleaning: Figure 55
Figure 55: Batch type washer disinfector with automatic door. A glass window allows seeing what's happening inside.

The Sterile Supply Cycle - Cleaning: Figure 56
Figure 56: Load carrier (insert) for hollow instruments. In order to ensure that hollow instruments (e.g. for MIS) are also cleaned inside, each individual instrument is connected to the water flushing system.

Batch type washer/disinfectors
These machines are also referred to as batch machines. This means that cleaning takes place in batches: a load is processed completely in a single chamber and then taken out of the machine. As opposed to tunnel or takt washers, in which the various phases of the process take place in a number of subsequent chambers.

Depending on its size a number of standardized instrument trays can be put on a load carrier (also called insert) and rolled into the cleaning chamber. Dedicated load carriers are available for a wide range of instruments and materials, covering such diverse applications as instruments, containers, MIS instruments, anaesthetic material, theatre clogs and baby bottles. Especially for hollow instruments it is essential that they are also cleaned and rinsed inside. Each instrument therefore is individually connected to the water flushing system. Depending on the type of load, a program can be selected. For newer machines inserts may have an indexing system that can be recognized by the machine and causes automatic selection of the appropriate cleaning program thus reducing the chance of human error of selecting the wrong program. The entire program runs fully automatic and takes place in the same cleaning chamber.

Advantages of these machines are

  • Compact design
  • Less complex then the tunnel washers; thus lower chances for break downs
  • Washing capacity can be increased by installing additional units side by side. This extra capacity gives back-up in case of break-down.

In case still larger capacities are needed the installation of tunnel washers can be considered.

Batch washer/disinfectors can be equipped as single door or double door units (Pass-through type). The pass-through type is recommended as it forces separation of the clean and dirty area, thus reducing chances for cross infection. The doors should be interlocked, making sure that only one door can be open at a time. Doors may be manually operated or can be fully automatic powered doors. When high capacity is needed multiple units can be fed by an automatic loading and unloading system.

The Sterile Supply Cycle - Cleaning: Figure 57
Figure 57: Simplified diagram for typical batch type automatic washer disinfector
The Sterile Supply Cycle - Cleaning: Fig. 58 - A tunnel-washer with four compartments
The Sterile Supply Cycle - Cleaning: Fig. 58 - A tunnel-washer with four compartments
Figure 58: A tunnel-washer with four compartments

Tunnel washer/disinfectors

In tunnel washer/disinfectors also referred to as takt machines, the load is put on a conveyer belt, which is passing through a number of compartments with doors closed during action, in each of which a subsequent step of the cleaning process takes place. In this way a tunnel washer may have e.g. 4 compartments: Prerinse, ultrasonic bath, main washing, and disinfection/drying.

As the machine simultaneously processes in all compartments, it can have a considerably higher throughput then the batch machines, and thus are used in locations where high volume cleaning capacity is needed.

A tunnel washer may turn out 30 or more instrument trays per hour. As the tunnel washer is not designed to clean complex instruments, with channels or corrugated airways, they must be manually cleaned or cleaned in a separate machine. Another disadvantage of such machines are their complexity and thus vulnerability for machine failures. Breakdowns will result in considerable reduction of cleaning capacity. Usually in facilities having tunnel washers also have one or more batch machines installed for back-up.

The Sterile Supply Cycle - Cleaning: Figure 59
Figure 59: Diagram of a tunnel washer, with the 4 chambers for each step of the cleaning process. Each phase can take place simultaneously. At any given moment there may be up to 4-8 trays being processed at the same time!

Personal protection when cleaning

Medical supplies that were used in the operating theatre may be heavily contaminated by microorganisms when they arrive at the department for cleaning. Thus cleaning is considered the most dangerous section of the sterilization department. In order to reduce the risks it is essential that precautions are taken to ensure safe handling during the cleaning process.

A first major principle is to limit contact with the materials as much as possible. That is why machine-cleaning is recommended whenever possible.

For protection during manual cleaning a range of materials is available

The Sterile Supply Cycle - Cleaning: Figure 60
Figure 60: During cleaning always wear gloves and apron


Wear gloves while cleaning instruments and equipment. Thick household gloves may work well.

Note: even when wearing heavy-duty utility gloves, care should be taken to prevent needle stick injuries or cuts when washing sharps! In case of an injury, follow the protocol for such injuries as prescribed by your hospital/facility.

When scrubbing ensure that any splashing moves away from you. Also you can do the scrubbing under water.

Plastic Apron

The apron will prevent moisture reaching clothes.

The Sterile Supply Cycle - Cleaning: Figure 61
Figure 61: Mouth mask and visor

The Sterile Supply Cycle - Cleaning: Figure 62
Figure 62: Goggles/visor

Mouth mask, visor and goggles

A mask will protect against breathing-in of splashes or droplets of aerosols. A visor or goggles give protection for your eyes.

The Sterile Supply Cycle - Cleaning: Figure 63
Figure 63: Splash screen

Splash screen

A splash screen above a cleaning basin can be used to prevent splashes entering eyes, mouth and nose. It reduces the need for wearing a visor and/or mask thus offering more breathing comfort. The screen should move smoothly and offer clear sight on the materials to be cleaned.


Quality control for cleaning

It is essential to know whether the cleaning process results in adequately clean equipment. Quality control in cleaning is currently a topic that is heavily under discussion and various test methods are being developed in order to verify the adequate cleaning. According to the new standard for automatic washer/disinfectors (prEN15883) the cleaning performance has to be validated for each type of load. This resulted in the development of standard test soils and process challenge devices for cleaning processes.

The Sterile Supply Cycle - Cleaning: Figure 64
Figure 64: Visual inspection

Visual inspection

The most basic verification of the performance of a cleaning process is by carefully inspecting the cleanliness of instruments and materials. All objects should be free of any remaining soils, deposits, pitting etc. Take special care for checking pivots, box joints, instrument serrations. Also cracks can be caused by corrosion, which again is a result of poor cleaning performance.

An inspection lamp with a magnifying glass can be very useful for identifying remaining residues.

The Sterile Supply Cycle - Cleaning: Figure 65
Figure 65: Test kit with UV lamp, fluorescent powder and fluid.
The Sterile Supply Cycle - Cleaning: Figure 66
Figure 66: Unclean areas light up bright

Fluorescent powder and fluids with Ultra Violet light

For demonstrating effectiveness of cleaning test kits is available. The kits use a fluorescent powder or fluid, which are applied to the instrument or materials. The materials are then cleaned in the normal way. By using an ultra violet light any particles/soil that were not removed will light up. A great educational tool! It clearly identifies the weak points in the cleaning procedure: usually teeth, joints and screws, all those places where soil can collect but which are easily forgotten. This kit can also be used for training on improving hand-washing procedures. As its quantities usually cannot be calibrated, these materials cannot be used for validation of the cleaning procedures.

The Sterile Supply Cycle - Cleaning: Figure 67
Figure 67: The TOSI: The strip is covered with a standardized test soil

The Sterile Supply Cycle - Cleaning: Figure 68
Figure 68: Simulating blood

Test Object Surgical Instruments

Several attempts are made in order to have a universal test soil for the verification/validation of the performance of washer disinfectors. The TOSI (Test Object Surgical Instruments) is becoming an accepted tool for testing cleaning performance. It is a metal strip, partially covered with a soil, with similar characteristics as human blood. The strip is half encapsulated in a plastic cover, designed such that access of the cleaning agent gets more difficult from one end to the other. They are calibrated such, that when a cleaning system manages to clean the device, it can be assumed that optimal conditions for cleaning of instruments will be achieved.

The Sterile Supply Cycle - Cleaning: Figure 69
Figure 69: Test object for hollow instruments

Test object for hollow instruments

For testing cleaning performance for hollow instruments test devices are available, simulating hollow instruments. A strip similar to the test strip for normal instruments, is put in a capsule, with lumens on both sides. The dimensions of the test object are similar to long hollow instruments. Its operation is the same as the normal test object.

The Sterile Supply Cycle - Cleaning: Figure 70
Figure 70: Test object for flexible endoscopes

Test object for flexible endoscopes

The test object simulates the lumen of a flexible endoscope. Its operation is similar to test objects for normal instruments and hollow instruments.

The Sterile Supply Cycle - Cleaning: Figure 71
Figure 71: Protein Test

Protein Test

These are test for the detection of blood residues on surfaces. So with such a test the cleanliness of the actual load items are tested. The tests are based on an enzymatic reaction. Minute residues will cause a quick colour change. Typical: 0,1 microgram within half a minute. A swab is used to take a sample from a surface, e.g. a surgical instrument. The swab is put in the indicator and check for the colour change (e.g. transparent to blue-green).

The Sterile Supply Cycle - Cleaning: Figure 72
Figure 72: Solid state data loggers for temperature, that can be used for the validation of cleaning processes

Data loggers
For a quantative analysis of a cleaning process it is essential to measure temperature and time throughout the cleaning cycle, in different locations of the load. Solid stated data loggers can be used for this purpose. After the process they can be connected to a computer and the process data loaded into a program for analysis of the process.

The Sterile Supply Cycle - Cleaning: Figure 73
Figure 73: Validation of washer disinfectors became a requirement

Validation of washer/disinfectors
According to new standards, the processes of washer disinfectors need to be validated. Clean products are a result of a well-loaded washer/disinfector in a well operating washer disinfector, running the right process. The cleanliness has to be verified against an accepted standard of cleanliness, in terms of residues and micro-organisms.

Validation: documented procedure for obtaining, recording and interpreting the results required to establish that a process will consistently yield products complying with predetermined conditions


General guidelines for cleaning practice

  • Whenever possible instruments should be cleaned and disinfected immediately after use.
  • Always clean brand-new instruments prior to first sterilization.
  • Carefully follow the Instructions for Use.
  • Strictly adhere to dosage, exposure time and temperature specifications provided for cleaning and disinfection.
  • Always open hinged instruments prior to preparation.
  • As far as possible, disassemble all instruments before treating them.
  • Be sure to use only suitable cleaning tools and accessories.
  • Do not overload washing machines and ultrasonic cleaning devices. Prevent the formation of "shadows" and anechoic zones.
  • Never use metal brushes or metal sponges for manual cleaning.
  • Rinse thoroughly and carefully after cleaning. If possible, use demineralized water.
  • Dry sufficiently after rinsing.
  • Worn, corroded, deformed, porous or otherwise damaged instruments must be sorted out and discarded.
  • For hygienic reasons, instruments must be sent through the complete preparation cycle before they are submitted for repair.
  • Hinged/jointed instruments must be treated with a paraffin oil-based lubricant (not applicable to flexible endoscopes and accessories).
  • Following assembly, subject each instrument to a functional test. Hinged instruments must be lubricated prior to carrying out the test.
  • Instruments with a ratchet should only be closed at the first tooth/notch before sterilization.
  • Sterilization is no substitute for cleanliness!

Taken from: Proper Maintenance of Instruments, Working Group Instruments Preparation, ArbeitsKreis Instrumenten-Aufbereitung, 1999.


Normative references (European)

Cleaning should meet minimum requirements that have been formulated by the CEN (European Standards Commission):

prEN ISO 15883
Parts 1-4
The standard describes:
  • Performance requirements
  • Mechanical and process requirements
  • Testing for conformity
  • In its appendices, among others, a test programme and a list of test soils used in a number of countries are included


Recommended literature related to cleaning


Websites related to cleaning

General information on instrument cleaning

Endoscope cleaning

Water: physics and chemistry

Soaps and detergents

Ultrasonic cleaning


Sources of photos/illustrations

Note: The photographs/illustrations not mentioned here are made by the author.

Fig. 4
Fig. 23
Fig. 26
Fig. 35
Working group for Instrument Preparation, Germany.
Fig. 22 Prof. Dr. Rüdiger Blume Universität Bielefeld, Fakultät für Chemie; Bielefeld, Germany.
Fig. 27
Fig. 28
Fig. 30
Fig. 31
Fig. 32
Silhorko-Eurowater A/S, Skanderborg, Denmark.
Fig. 29 Barnstead, Boston, USA.
Fig. 33
Fig. 36
Dr. Staffeldt, Chemische Fabrik Dr. Weigert GmbH & Co. KG, Germany.
Fig. 38 Spectrum Surgical Instruments Corp. USA.
Fig. 43
Fig. 45
Fig. 47
Fig. 48
Branson Ultrasonics Corporation USA.
Fig. 50 Sentry Products, United Kingdom.
Fig. 51
Fig. 52
Fig. 53
Fig. 67
Fig. 68
Fig. 69
Fig. 70
Fig. 71
Pereg GmbH, Germany.
Fig. 55
Fig. 56
Fig. 57
HAMO AG Reinigungs und Hygienetechnik, Pieterlen/Biel, Switzerland.
Fig. 58
Fig. 59
Fig. 73
Belimed GmbH, Germany.
Fig. 62 Medisafe, UK.
Fig. 65 Deb Benelux bv., The Netherlands.
Fig. 66 Missionsärztliches Institut, Wuerzburg, Germany.
Fig. 72 Ebro Electronic GmbH & Co, Germany.

WFHSS - World Forum for Hospital Sterile Supply » Education » General » Sterilization Basics » Cleaning

© 2011 WFHSS • Updated: 30 October 2010, 10:56 [GMT]