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Chapter: 11th 12th std standard Class Nursing Health Care Hospital Hygiene Higher secondary school College Notes

Methods of Disinfections and Sterilisation

Methods of Disinfections and Sterilisation
1.Mechanical a. Scrubbing b. Filtration c. Sedimentation. 2. Physical a. Moist heat i. boiling ii. steam under pressure iii. pasteurization. b. Dry heat. Baking. Incineration Flaming. Sunlight. c. Low temperature. 3. Chemical. - use of disinfectants such as Phenol lysol etc.



1.     Mechanical


a.     Scrubbing

b.     Filtration

c.      Sedimentation.


2.     Physical


a.     Moist heat

                                                             i.      boiling

                                                           ii.      steam under pressure

                                                        iii.      pasteurization.

b.     Dry heat. Baking. Incineration Flaming. Sunlight.

c.      Low temperature.


3.     Chemical. - use of disinfectants such as Phenol lysol etc.




1.     Scrubbing: Hand washing is one of the important procedures of a nurse in order to control and prevent self-infection as well as cross infection. Scrubbing and washing the hands with soap and water removes the organisms mechanically.

2.     Filtration: In laboratories fluids are sterilized by filtration. The process of filtration aids in retaining certain bacteria.


3.     Sedimentation: It is used in the purification of water. By this method the suspending materials together with bacteria settles down in the bottom of liquid.




1.Moist heat:


Boiling - Boiling at 100 C for 3 to 5 minutes kills microorganisms except spore bearing organisms such as bacillus tetani. There are certain rules to be observed while boiling.


Scrub and clean the articles to remove organic matter, which will coagulate around the organisms and protect them.

Articles except the glass should be put at the boiling point of water (great care should be taken for glass articles, and they should be wrapped with cloth and put in cold water and then brought to boil).

Articles should be well covered by the water and boiled for the required length of time.

Steam under pressure:

Spore bearing organisms are killed by steam under pressure. Autoclave is an apparatus used for sterilization of articles by steam under pressure.

In this, the steam is allowed to circulate in a closed container and it is compressed and thereby raises the temperature above the boiling point of water (121 C).

In this method the articles are sterilized under 15 pounds pressure of steam for 15 to 20 minutes. Materials sterilized by autoclaving method are dressings, gloves, linen, syringes, certain instruments and culture medias.



Pasteurization is a method of sterilizing milk. Milk is heated to a temperature of 60 C for half an hour and rapidly cooled to 13 C. This aids in destroying all pathogenic organisms and reduces acid-producing organisms and thus prevents souring of milk.

2). Dry Heat:



This method of sterilization is used in sterilizing glassware, syringes, needles, culture tubes and medias. Most of the vegetative forms of bacteria are killed. Spores need to be heated for 1 to 2 hours. The apparatus used for baking is known as 'hot air oven'.



In order to destroy all organisms, infected wound dressings, contaminated materials, garbage and other hospital wastages etc are burnt by incineration. The apparatus used for this complete burning is incinerator.


This is used in sterilizing platinum loops in laboratory and also in sterilizing needles and instruments. This aids in killing organisms.



The ultra-violet rays from sunlight have the effect of destroying a large number of bacteria. Blankets, pillows, mattress are disinfected by sunlight. Care should be taken to turn the articles often to kill the microorganisms on both surfaces.


3). Low temperature:


Cold has the effect of decreasing or completely stopping the growth of bacteria. Constant freezing will destroy bacteria.








Certain chemicals are used in disinfection of articles like thermometer and also the disinfection of floor and decontamination of infected linen etc.


Principles to be observed:


1.     All articles contaminated with blood, faeces, pus, sputum, or other substances must be rinsed with cold water to prevent coagulation of protein material.

2.     Use soap and water for cleaning the instruments and use a brush whenever necessary.

3.     Allow sufficient time for articles to be disinfected or sterilized by physical or chemical agents.

4.     It is important to select the right disinfectant, the right strength and the right time.

5.     Use the right procedure to render instruments and other articles safe for further use in order to prevent the spread of infection.

Chemical substances, which are commonly used.


Dettol:This is widely used chemical for sterilization of instruments, thermometer etc. It is non-poisonous and non-irritant to the skin. 5 to 50% solution is used for dressings and wound irrigation.

Savlon: 1:30 savlon solution is used to destroy or kill vegetative bacteria.

Chloride of lime(Bleaching powder): This is used for disinfection of drinking water, stools, urine, sputum. As it decomposes quickly when exposed to air. Solutions must be made fresh for each use.


Formalin: A 40 percent solution is used to disinfect faeces, urine and sputum. It is not used for the skin and tissues, as it is an irritant.


Tincture of Iodine: 1-2 percent iodine is used for cleaning skin and treating injuries to the skin.

Hydrogen peroxide: 1-5 percent of solution is used in cleaning wounds and to remove pus from infected ears. Hydrogen peroxide is also used to clean the mouth. It is an oxidizing agent.

Potassium permanganate: It is an oxidizing agent used for cleaning the mouth 1:1000 strength. It is also used for irrigation of wounds.


Carbolic acid (Phenol): It is a good disinfectant for faeces, pus, blood and sputum. It is a skin irritant and a poison. Dissolves easily in hot water. For thermometers 1:20 solution for a duration of 10 minutes.


Lysol: This is a phenol or chlorasol preparation mixed with soap. It is less poisonous than a carbolic acid but has a greater bacteriocidal action. 2 % solution for 6-8 hours is used for disinfecting linen.

Ethyl alcohol 70% is effective for skin disinfection. Certain gases like formaldehyde and gluteraldehyde are used in disinfection of rooms


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