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Infection Control

The science of steam vapor systems

September 19, 2010
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The power of steam has been harnessed for many purposes over the years.

For example, steam is used in the medical profession for sterilization of instruments and critical materials.

Traditionally, steam has been generated using bulky, non-mobile equipment.

In hospitals, for example, steam is applied in autoclaves often weighing over 1,000 pounds and permanently connected to the hospital’s water and wastewater systems.

In recent years, advances in technology have made it possible for the highest-quality steam to be generated by much smaller — even portable — steam vapor systems.

The importance of cleaning
Cleaning is important for several reasons.

First, cleaning imparts a pleasant appearance and greater acceptability for surfaces and objects.

Second, cleaning removes substances that may be toxic, such as chemical residues, which can trigger allergic and immunological reactions.

Third, dirty surfaces must be cleaned before disinfection can take place, since many disinfectants react with soils rendering them useless in some instances.

Fourth, cleaning a surface or object helps ensure that accumulated soil will not interfere with its desired function. For example, surfaces impregnated with germ-killing metal ions, such as silver or copper, are rendered ineffective if they become soiled or dirty.

Finally, cleaning removes embedded microscopic soils that may otherwise provide shelter and nutrients for microorganisms.

When water is introduced into these nutrient-rich environments, such as restrooms, germs may reproduce rapidly.

Removing the ubiquitous, but often invisible, food supply for microorganisms limits the growth of the microbial population, while also reducing the risk of cross-contamination to people and objects.

Cleaning strategies
There are three basic ways to clean an object or surface: Physical abrasion, detergent chemicals/solvents, and heat/steam.

Each strategy has benefits and drawbacks.

Briefly, physical abrasion is effective for stubborn soils, but will scratch many surfaces and cannot remove soils embedded in microscopic pores, nooks and crevices.

Detergent chemicals and solvents are effective for certain types of soils, but may be toxic to humans, damage surfaces, or adversely affect the environment.

Heat and steam are effective for removing many types of soils, but require an energy source, typically electricity.

Advantages of steam for cleaning
Heat is energy and energy does work.

Water, by its nature, has a very high “specific heat,” or ability to hold heat energy.

Thus, saturated steam is a very efficient vehicle for delivering heat energy to a surface.

The transfer of heat energy to surfaces is crucial to cleaning since it disrupts the bonds that hold dirt to surfaces and in many cases liquefies the soil itself, making it available for removal.

One key advantage of steam — and its associated energy — is its ability to penetrate deeply and quickly into nooks, crevices and microscopic pores in surfaces.

By doing this, steam vapor reaches far beyond traditional cleaning processes.

Since steam tends to release its heat energy upon contact with the target surface, accumulated soils and other residues are disintegrated and easily removed, without chemicals or labor-intensive scrubbing/
abrasion.

The importance of surface disinfection
Microorganisms, as the term implies, are very small and the vast majority are invisible to the eye.

Therefore, microorganisms reside in tiny spaces, especially on textured and porous surfaces, and elude many cleaning processes.

With the emergence of new pathogens and the re-emergence of some evolving classic pathogens, it has become important to clean beyond what we can see.

While some microorganisms are mainly spread by aerosols, food, or water, others may be easily transmitted from person to person by contaminated surfaces.

Obviously, it is important to disinfect environmental surfaces that may be involved in the transmission of disease.

Disinfection strategies
There are three basic technologies that can be used to kill microorganisms on surfaces.

The first, and by far the most common technology, is the liquid chemical disinfectant.

These products usually contain sodium hypochlorite, quaternary ammonium compounds, or phenols.

They can be effective when used in strict compliance with label instructions, but are not always practical because of personal protective equipment (PPE) requirements, lengthy contact or dwell times, potential for interference by/reaction with other chemicals, allergenic attributes, and the general inability of chemicals to disinfect porous surfaces.

The second strategy that can be used for surface disinfection is incorporation of antimicrobial compounds into the surfaces themselves.

While some of these technologies are promising, they are in their early stages of development, not regulated by the Environmental Protection Agency (EPA), and generally have not been proven to keep surfaces free from microorganisms.

Steam as a disinfectant
Steam kills germs by the destructive action of the steam/heat on microbial proteins — and also by destruction of the fatty cellular membranes of bacteria and fungi.

Once sufficient heat has been conveyed to the surface by the steam such that live microorganisms are no longer present, it is disinfected.

Steam is a reliable and time-tested disinfection technology.

In fact, steam autoclaves are considered the gold standard for sterilization of medical devices since steam leaves no chemical residues behind and steam is active against a broad range of microorganisms, including those that resist chemical disinfection.

Scientific validation
When considering the use of any disinfectant, it is important that the user be assured of a positive outcome.

The table shown on page 35 highlights the capabilities of a particular modern portable steam vapor system that was designed specifically for surface disinfection and tested using protocols developed to reflect those required by the EPA for traditional chemical disinfectants.

Testing was performed by third-party commercial microbiology laboratories, including Antimicrobial Test Laboratories, Nelson Labs, and Microbiotest.

The unit tested was a VaporJet 2400 with the “TANCS” option, provided by Advanced Vapor Technologies.

Tests were performed in duplicate, as follows:
  1. Microorganisms were grown in liquid culture or harvested from stock suspensions.
  2. Artificial soil was added to the culture.
  3. The culture was applied to a test surface.
  4. Microorganisms were allowed to dry on the surface.
  5. Contaminated surfaces were treated with the portable steam vapor system for various periods of time.
  6. After contact, surviving microorganisms were enumerated and percent reductions were reported.
The test results show one of the most important aspects of disinfection using steam vapor: Microorganisms are eliminated much more rapidly than is possible with traditional chemical disinfection technologies.

In addition to the data shown, recent studies also suggest that brief intermittent exposures to dry steam vapor, such as a surface would receive if a steam cleaning head were to be passed over the same spot multiple times, are as effective at disinfection as longer continuous exposures.

That is, five one-second exposures appear to have the same effect as one five-second exposure (data not shown).

The implication of these studies is that the steam vapor systems can be used in a normal, natural fashion and disinfection is rapidly achieved.

One of the most important ramifications of modern portable steam vapor systems is that the disinfecting power of steam can now be applied to contaminated surfaces in an easy and safe fashion.

Extensive laboratory testing has shown that steam disinfection of environmental surfaces is a reliable way to quickly eliminate microorganisms from surfaces within seconds.

Since steam penetrates pores that many chemicals and abrasive cleaners cannot, steam is a thorough, reliable means of surface disinfection.

Practicality of modern portable steam vapor systems
From a practical perspective, modern portable steam vapor systems require only a small amount of electrical power and water.

The systems convert common tap water into super-heated “dry” steam.

The process requires no toxic chemicals and therefore no Material Safety Data Sheets (MSDS).

Portable steam vapor systems provide a safer and simpler process than disinfection using liquid chemical disinfectants.

Portable steam vapor systems pose little if any ancillary risk for humans or building occupants and eliminate the need to maintain long “wet dwell” times or the need to rinse a treated surface.

The steam vapor cleaning and disinfection process is appropriate for any washable surface and is especially effective on irregular, uneven, or textured surfaces.

High-touch equipment, such as wheelchairs, water fountains, food carts, and hospital bed rails, surfaces can be quickly and frequently treated to maximize risk reduction where cross-contamination is a concern.


Benjamin D. Tanner, Ph.D., is the president of Antimicrobial Test Laboratories (www.AntimicrobialTest
Labs.com). He may be reached at Ben@Antimicrobial
TestLabs.com.

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