Sterilization can be achieved through physical or chemical methods. Physical methods include heat (dry heat or moist heat using autoclaves), filtration, and radiation (UV or X-rays). Chemical sterilization involves the use of gases like ethylene oxide or liquids/solutions such as alcohols, phenols, and aldehydes. Common sterilization techniques are dry heat in hot air ovens, moist heat in autoclaves using pressurized steam, ethylene oxide gas, and alcohol or phenol solutions. Each method has advantages and disadvantages depending on the material to be sterilized and effectiveness against different microorganisms.

1. Sterilization

2. Principles and methods of sterilization
Sterilization mainly classified into two types
1.Physical method
2.Chemical method

3. 1.Physical method
I. Heat
II. Filtration
III. Radiation Method

4. Heat
A. Dry heat - Hot air oven
B. Incineration
C. Moist heat- Autoclave, Pressure cooker
D. Tyndallization (Fractional sterilization)

5. A. Dry heat - Hot air oven
In dry heat sterilization, dry heat is used for sterilizing different materials.
Heated air or fire is used in this process. The temperature is usually higher
than 356° F or 180 °C.
Example: Hot air oven
Principle of HOT AIR OVEN :
Sterilizing by dry heat is accomplished by conduction. The heat is absorbed
by the outside surface of the item, then passes towards the Centre of the
item, layer by layer. The entire item will eventually reach the temperature
required for sterilization to take place.

6. Dry heat does most of the damage by oxidizing molecules. The
essential cell constituents are destroyed and the organism dies.
The temperature is maintained for almost an hour to kill the most
difficult of the resistant spores.
The most common time-temperature relationships for sterilization
with hot air sterilizers are
170°C (340°F) for 30 minutes,
160°C (320°F) for 60 minutes,
150°C (300°F) for 150 minutes or longer depending up the volume.

7. Advantages
Hot air ovens use extremely high temperatures over several hours to
destroy microorganisms and bacterial spores.
The ovens use conduction to sterilize items by heating the outside
surfaces of the item, which then absorbs the heat andmoves it
towards the center of the item.
Disadvantages
Time consuming method because of slow rate of heat penetration
and microbial killing.
High temperatures are not suitable for most materials.

8. B. Incineration
Incineration is a waste treatment process that involves
the combustion of organic substances contained in waste materials.
Incineration and other high-temperature waste treatment systems
are described as "thermal treatment". Incineration of waste materials
converts the waste into ash, flue gas and heat.

9. C. Moist heat- Autoclave
Water at high pressure level is used in moist heat sterilization.
Autoclave is the instrument in which this process is carried out.
Example: Autoclave, Pressure cooker
Autoclaves principle :
High-pressure steam sterilization (autoclaving) to kill all
microorganisms, including spores , sterilization is the best, the most
widely used methods of sterilization.
At 103.4kPa (1.05kg/cm2) vapor pressure , the temperature reached
121.3 ℃, for 15 ~ 20 minutes .

10. Uses of Autoclave:
Autoclaving is used to sterilize culture media, instruments, dressings,
intravenous equipment, applicators, solutions, syringes, transfusion
equipment, and numerous other items that can withstand high
temperatures and pressures.
The laboratory technician uses it to sterilize bacteriological media and
destroy pathogenic cultures.

11. D. Tyndallization (Fractional sterilization)
 Tyndallization is a process dating from the nineteenth century
for sterilizing substances, usually food, named after its inventor,
scientist John Tyndall, that can be used to kill heat-
resistant endospores. Although considered old-fashioned, it is still
occasionally used.
 Tyndallization essentially consists of heating the substance to boiling
point (or just a little below boiling point) and holding it there for 15
minutes, three days in succession.

12. Filtration
Types of filters
A. Seitz filter
B. Membrane filters

13. A. Seitz filter
Seitz filter A filter disc (originally of asbestos) with pores so fine that
they will not permit passage of bacteria; solutions emerge sterile.

14. B. Membrane filters
Membrane filters have a known uniform porosity of predetermined
size (generally 0.45 µm ) sufficiently small to trap microorganisms.
Using the membrane filter technique, sample is passed through the
membrane using a filter funnel and vacuum system.
Any organisms in the sample are concentrated on the surface of the
membrane. The membrane, with its trapped bacteria, is then placed
in a special plate containing a pad saturated with the appropriate
medium.

15. The passage of nutrients through the filter during incubation
facilitates the growth of organisms in the form of colonies, on the
upper surface of the membrane. Discrete colonies thus formed can
be easily transferred to confirmation media.
Membrane filter technique is an effective, accepted technique for
testing fluid samples for microbiological contamination.

16. Radiation Methods
A. UV Radiation
B. X-rays

17. A. UV Radiation
UV light sterilization is an environmentally friendly method of killing
bacteria, mold, fungi, and viruses without the use of harmful
chemicals and does not produce corrosive materials or disinfection
by-products (DBPs).
or
short-wavelength ultraviolet (UV-C) light to kill or
inactivate microorganisms by destroying nucleic acids and disrupting
their DNA, leaving them unable to perform vital cellular functions.

18. Advantages:
It does penetrate air, effectively reducing the number of airborne
microorganism and killing them on surfaces on operating rooms and
rooms that will contain caged animals.
To help sanitize the air without irradiation humans, these lights can be
turned on when there rooms are not in use.
Disadvantage:
A major disadvantage of UV light as a disinfectant is that the radiation is
not very penetrating, so the organism to be killed must be directly
exposed to the rays.
Another potential problem is that UV light can damage human eyes, and
prolonged exposure can cause burns and skin cancer in humans. And it
may cause damage in human skin cells and permanent damage the eyes.

19. B. X-rays
X-rays make up X-radiation, a form of electromagnetic radiation.
Most X-rays have a wavelength ranging from 0.01 to 10 nanometers.
It have good penetration.
A wide variety of healthcare products from implants to
pharmaceuticals employ X-ray technology’s sterilizing capability, while
industrial applications from semiconductors to micro-etching can
benefit from its use.

20. 2.Chemical method or Disinfections
A. Ethylene oxide
B. Alcohols
C. Phenols
D. Aldehydes

21. A. Ethylene oxide(EO or EtO)
Ethylene Oxide (also known as EO or EtO) sterilization is a simple
chemical compound that is commonly used for gaseous sterilization of
disposable medical devices and healthcare products.
EtO gas infiltrates packages as well as products themselves to kill
micro organisms that are left during production or packaging
processes.
This gas, mixed with air at a ratio of at least 3% EtO gas, forms an
explosive mixture. Pure EtO gas boiling point is 10.73 ºC at
atmospheric pressure.

22. Most of the time, it is mixed with Nitrogen or CO2. This explosive
condition requires Intrinsic Safe material (ATEX) zoning, for security of
people as well as security of the process itself.
Safety of personnel is an important issue due to the harmful effect of
EtO on humans.
When this toxic gas is removed from the room it needs to be treated
using thermal burners, scrubbers or oxidation for environmental
protection or be transported to an alternate facility for treatment.

23. B. Alcohols
The types of alcohol used in disinfection are ethanol (80%), propanol
(60%), and isopropanol (70%).
Alcohols are quite effective against bacteria and fungi, less so against
viruses.
They do not kill bacterial spores. Due to their rapid action and good skin
penetration, the main areas of application of alcohols are surgical and
hygienic disinfection of the skin and hands.
One dis-advantage is that their effect is not long-lasting (no depot effect).
Alcohols denature proteins.

24. C. Phenols
Lister was the first to use phenol (carbolic acid) in medical applications.
Phenol derivatives substituted with organic groups and/or halo-
gens (alkylated, arylated, and halogenated phenols), are widely used. One
common feature of phenolic substances is their weak performance against
spores and viruses.
Phenols denature proteins.
They bind to organic materials to a moderate degree only, making them
suitable for disinfection of excreted materials.

25. D. Aldehydes
It can be used in a special apparatus for gas sterilization.
Formaldehyde is a water-soluble gas.
Formaldehyde is a broad-spectrum ger-micide for bacteria, fungi, and viruses.
At higher concentrations, spores are killed as well.
This substance is used to disinfect surfaces and objects in 0.5–5% solutions.
 It was commonly used in gaseous form to disinfect the air inside rooms (5
g/m3).