Sterilising Methods

Infection containment
Effective protection
against hazards we can’t see

Anything sterile is like a desert. Nothing lives, it is organic zero.

Sterilising something is to kill all trace of life. Life, that is, that is hazardous to humans,  though many sterilising agents are lethal if not handled with care.

The life forms that are killed of course are those that threaten human life by their own existence – usually elements of disease and sickness such as fungi, bacteria, viruses and spores.

Sterilising can be achieved by heat, chemicals, irradiation, high pressure or filtration – sometimes in combination.

Heat
Heat is the oldest method of sterilising, going back to prehistoric times.

  • Flaming – subjecting an object to direct flame until it glows hot, burning off impurities
  • Incineration – burning an object until it is reduced to ash, destroying any hazard
  • Boiling – immersing an object in water and subjecting it to high heat for a period of time
  • Steam heat sterilises by applying concentrated heat – often under pressure, as in an autoclave – frequently used for surgical instruments

Chemical

  • Ethylene oxide is a gas often used to sterilise objects that are sensitive to temperatures above 60°C – such as plastics, optics and electrics. It is slow acting, requiring a minimum of 3 hours exposure. It is also highly inflammable, toxic and carcinogenic – which requires careful aeration after treatment to remove hazardous residues.
  • Nitrogen dioxide is a gas that degrades the DNA of pathogens by nitration. It is very effective and quick acting, but as a gas is hazardous to use.
  • Ozone is an extremely powerful oxidiser, frequently used in the sterilisation of water. A corrosive gas, it is both highly toxic and unstable, requiring great care in handling.
  • Ammonium chloride, or didecyl dimethyl ammonium chloride (DDAC), is a strong oxidiser, one of several quaternary ammonium cations – known as quats – which destroy microbials by disrupting their cell membrane.
  • Sodium hypochlorite, more commonly known as chlorine bleach, is probably the most familiar household sterilising agent. It is highly corrosive, needs time to work – a minimum of 20 minutes immersion is the norm. It also decomposes on exposure to air, so usually has to be prepared fresh.
  • Formaldehyde is a slow-acting sterilant, requiring 24 hours immersion or more. It is volatile and toxic, both to the skin and to breathing.
  • Hydrogen peroxide is a powerful oxidiser, made naturally in the body as a germ-fighter, often used to disinfect wounds and familiar to many as a bleach for treating hair. In its ionised form it is used in Hypersteriliser machines to eliminate all viruses and bacteria.
  • Silver’s power to heal and fight infection was known to the ancient Greeks. Prior to World War One it was THE treatment for infection, before the discovery of antibiotics. As silver sulfadiazine cream it was also the standard of care for serious burns until the 1990s. Its antibacterial action is accelerated by the presence of an electric field.

Radiation

  • Ultra violet light is an effective steriliser across the board, particularly where direct contact must be avoided. As a light ray of course, it is ineffective in shaded areas and requires realignment to provide full cover. It is damaging to some plastics.
  • X-rays, gamma rays and radioisotopes are high energy treatment , for bombarding objects under tightly controlled conditions.

Pressure

  • High pressure treatment, often referred to as pascalisation, is a technique used in the sterilisation of food.

Filtration

  • Filtration is used mainly in the treatment of water and sewage.
  • High efficiency particulate air (HEPA) filters are also used in hospital and aircraft to capture harmful pathogens down to 3 microns across.

Concentrations and Uses of Hydrogen Peroxide

  • 3% General Disinfectant: Usually available at your chemist. For treatment of cuts and open wounds. Not for internal use.
  • 6% Cosmetic Colourant: Used by hair salons to bleach hair. Not for internal use. In ionised form, this mild concentration becomes a powerful oxidising airborne antimicrobial with a 6-Log Sterility Assurance Level – equivalent to 99.9999% viruses and bacteria destroyed.
  • 30% Laboratory Agent: Used for a variety of scientific. Dangerous taken internally.
  • 32% Industrial Cleanser: For cleaning intricate electronic parts. Dangerous taken internally. In vaporised form, this strong solution is deployed as an airborne antimicrobial with a 6-Log Sterility Assurance Level. With a high moisture content, extensive drying is required after application.
  • 35% Food Production: A disinfectant/steriliser used in production of cheese, eggs, and dairy. Often applied to foil packaging of fruit juices and milk-based products.
  • 90% Oxygen source for rocket fuel.