Equipments Employed In Large Scale Sterilization

(A) Moist heat sterilization:

Autoclave: The object to be sterilized is exposed to saturated steam under 1 Atmosphere pressure at a minimum temperature of 121°C for 15 minutes where microorganisms are destroyed by cellular protein coagulation. It is a device to sterilize equipments and supplies by subjecting them to high-pressure saturated steam at various temperatures and times (Table 2.6). Two types of autoclaves are used likely portable autoclaves and stationary autoclaves. A stationary autoclave is used as a large-scale sterilizer.

Table: Working conditions of an Autoclave at various temperatures and times

Temperature (degree C)	Pressure (lb/sq.inch)	Time (Minutes)
115-118	10	30
121-124	15	15
126-129	20	10
135-138	30	3

Working of Autoclave: 3 All autoclaves operate on similar principles that they share with a common kitchen pressure cooker - the door is locked to form a sealed chamber, and all air within the chamber is replaced by steam. The steam is then pressurized to reach the desired sterilization temperature and time, before exhausting the steam and allowing the goods to be removed. The various phases of a sterilization cycle are given below (Fig).

1. Purge Phase: Steam flows through the sterilizer beginning the process of displacing the air; temperature and pressure ramp slightly to a continuous flow purge.

2. Exposure (Sterilization) Phase: During this phase, the autoclaves’ control system is programmed to close the exhaust valve causing the interior temperature and pressure to ramp up to the desired set point. The program then maintains the desired temperature (dwells) until the desired time is reached.

3. Exhaust Phase: The pressure is released from the chamber through an exhaust valve and the interior is restored to ambient pressure, although contents remain relatively hot.

Fig: Phases of sterilization cycle

(B) Dry heat sterilization:

Hot air oven: It is an electrical device, and uses dry heat to sterilize. It was originally developed by Pasteur. Generally, it can be operated from 50 to 300°C, using a thermostat to control the temperature. It requires direct heat at different times and temperatures (Table).

Table: Working condition of hot air oven

Temperature (degree C)	Time (Minutes)
170	60
160	120
150	150
140	180

Working: The working of the hot air oven is based on the hot air inside the chamber of the oven by forced circulation. When hot air reaches the top of the chamber, it is circulated back to the bottom by a fan installed inside the chamber, and hence the optimum amount of heat is achieved gradually inside the hot air oven. After heating the content of the oven for two hours at 160°C, the articles are allowed to remain there, till the temperature comes down to 40°C. The sterilized materials are then removed from the oven.

Pharmaceutical Applications:

1. It is mainly used for the sterilization of glassware such as pestles and mortar, Petri dishes, flasks, pipettes, bottles, test tubes, etc.

2. It is used for the sterilization of powders such as sulfacetamide, sulphadiazine, kaolin, zinc oxide, starch, etc.

3. Injections where fixed oils are used as the vehicle, are sterilized by the dry heat method like, injections of progesterone, injection of testosterone propionate, and injections of oestradiols dipropionate.

4. It is also used for the sterilization of scalpels, scissors, spatula, blades, and glass syringes.

5. The chemicals, and glassware in laboratories, research institutions, industries, hospitals, and R&D centers use hot air ovens that are suitable for temperatures up to 250°C.

6. Hot air ovens are suited to various applications like heating, drying, sterilizing, and baking.

Microwave: Electromagnetic radiation is transmitted in waves or particles at different wavelengths and frequencies. This broad range of wavelengths is known as the electromagnetic spectrum. The spectrum is generally divided into seven regions in order of decreasing wavelength and increasing energy and frequency. Electromagnetic energy in the microwave region (225 MHz to 100 GHz, especially 2,450 MHz) is extensively used as an alternative energy source for sterilization. In a microwave oven, heat is a byproduct and is controlled by temperature probes where sterilization is also achieved at 40°C.

Sterilization methods are carried out with the use of microwaves where a bactericidal solution is used for heating. The technique is being promoted for use with dental instruments and relies on heating a solution of a quaternary ammonium compound (benzalkonium chloride) to approximately 100°C. At present, these processes are applicable only to unpackaged instruments. Dry spores of Bacillus subtilis and B. niger are treated with heat simultaneously in a convection dry-heat oven and a microwave oven.

Principle: Microwaves are radio waves and the commonly used radio wave frequency is roughly 2,450 megahertz (2.4 gigahertz). These waves are absorbed by water and other nutrients and then converted directly into atomic motion and motion is converted into heat.

Working: The microwaves are generated in a microwave by a device called a magnetron, which converts electricity from the power outlet into microwaves. These microwaves are absorbed by water molecules from the inside materials, which are rotated by the electric field from the microwaves. As these molecules rub against each other, they heat up, and then they heat up molecules around them (Fig).

Fig: Working of microwave

(C) Colour-coded biomedical waste bags:

Various colored coded bags are used for particular materials for disposal. They are discussed below (Table).

Table: Functions of various colored bags

Yellow plastic bags	For human anatomical, animal, and microbiological waste
Red disinfected container or plastic bag	Microbial waste
Blue or white plastic bag	Disposable tubing
Black plastic bags	Discarded medicines, incineration ash