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Infection Control

Science-based Steps Of The Cleaning Process: Part Five

September 19, 2010
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Heat''s Role In Cleaning

Heat — as measured by temperature — is an important element in cleaning, especially its affect on the solvents breaking down pollutants.

Usually as temperatures increase most solid and liquid substances in a liquid solvent become more soluble.

Heat always improves cleaning''s effectiveness by increasing reaction rates and dissolving abilities caused by entropy.

Even without soap, small amounts of grease will dissolve in water.

The dissolved amount increases in hot water, sometimes ten-fold.

Heat contributes to melting making it easier for soapy water to penetrate, detach and surround the unwanted matter.

Temperature solubility varies among substances.

As the temperature of the solution in which a substance is being dissolved increases, however, the substance dissolves faster and more completely.

Without heat, solubility becomes more a state of equilibrium.

The substance breaking down dissolves at the same rate it rejoins or crystallizes.

When introduced into the cleaning solution heat sets matter in motion.

This momentum keeps dissolved particles from sticking when they collide.

Instead they bounce off each other or disperse in an expanding fluid.

Elevated temperatures increase cleaning''s effectiveness and require less solvent to dissolve a specific amount of substance.

Increased temperature conditions a liquid solvent to dissolve elements quicker.

Traditionally, moist and dry heats control disease by killing or controlling harmful living organisms.

Both have advantages and limitations.

At ambient or normal pressure boiling water kills organisms, sanitizes and disinfects.

Generally, however, this process is not used as a sterilizing agent because of its relatively low temperature.

In contrast, steam is hotter under pressure, relatively inexpensive and rapidly sterilizes materials and exposed surfaces.

Dry heat requires high temperatures for cleaning which makes using it expensive.

It will, however, penetrate oils and other water-resistant materials.

Destroying living organisms with heat depends on:

  • The organism''s ability to resist heat
  • What temperatures can be achieved
  • How long the heat can be delivered to the organism.

Some living organisms can survive in extremely high temperatures.

For example, to destroy (deactivate) 100,000 bacterial spores of stearothermophilus they must be exposed to steam at 121 degrees Celsius for at least 12 minutes.

Destroying 1,000,000 spores of the bacteria species subtilis at the same temperature takes one minute.

This example reinforces the belief that heat affects each biological pollutant differently.

Consequently, we must know the nature and characteristics of the living matter we are trying to destroy and remove.

Routinely cleaning the built environment requires sterilizing, sanitizing and disinfecting.

A condition must be created that accepts environmental risks.

Heat assists this process by destroying bacterial cells and spores even though the living organism population rarely can be destroyed completely.

Repeated cleaning at high temperature controls harmful living organism populations.

How Does Reactivity Relate To Cleaning?

Generally, gaseous solutions do not work well in cleaning because their molecules are too widespread when circulating in the air.

This weakens the attraction between the cleaning gas'' molecules and those of the pollutant being removed.

Gases are more effective when they are pressurized or highly concentrated in an enclosed vessel.

The closer the molecules are the more effective the cleaning.

Ozone is the gas solution frequently used in cleaning.

It reacts with other substances and changes their chemical structure.

Sometimes this reaction changes a substance''s smell and reduces its toxicity.

Ozone''s highly reactive nature purifies air and water and deodorizes and destroys microorganisms in water.

Some ozone properties make it an effective cleaning agent.

This is particularly true of its reactivity with organic chemical substances and lower life forms that are responsible for the toxic properties of ozone in humans.

Ozone reacts with man''s bioorganic compounds in the fluids, cells and tissues it contacts, especially those lining the respiratory tract.

This negative property calls for establishing ozone standards based on health needs.

Organic compounds react with ozone in a process similar to combustion.

This reaction produces carbon dioxide, water and an elemental oxide, such as ethylene, which has a distinct odor.

When exposed to ozone it breaks down into carbon dioxide, water and oxygen, all of which are odorless and harmless.

Some compounds — mostly inorganic — will not react with ozone, including silica, hydrogen peroxide and sodium bromide.

It is important to know in advance whether ozone will reduce a compound and, if so, what products are formed by that reduction.

Avoid ozone exposure when it is used in cleaning.


Michael D. Berry, Ph.D., was chairman of the Science Advisory Council for the Cleaning Industry Research Institute (CIRI) in 2006. The information contained in this article was extracted from Dr. Berry''s papers and presentations at CIRI''s 2007 Cleaning Science Conference and Symposium. His entire paper and PowerPoint presentation, as well as those of other symposium presenters, are available at www.ciri-research.org.

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