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Disinfection and sterilization are two different concepts. The disinfection and sterilization methods commonly used in biological clean room are compared, and three common methods such as ultraviolet sterilization, formaldehyde disinfection and ozone disinfection are described.

 Part 1 Foreword 

According to data, the human body about every 6~7cm2 of skin can carry 1~10000 bacteria, of which about 1% is pathogenic, human breathing, speech will also emit bacteria. Obviously, for clean workshops, especially biological clean rooms with relatively high cleanliness requirements, it is crucial to prevent the generation, removal and elimination of bacteria. Disinfection and sterilization are two effective methods to remove and destroy bacteria and ensure the microbial requirements of biological clean rooms.

 Part 2 Disinfection and sterilization are two different concepts 

Disinfection and sterilization are two different concepts. Sterilization, which is to kill or remove all microorganisms (including bacteria, viruses, etc.) in a substance, has absolute significance. That is to say, corresponding to sterilization is not sterilization, there is no intermediate state of more and less sterilization. In this respect, absolute sterilization is almost non-existent because it is difficult to achieve or for an infinite period of time.

Disinfection is a treatment that kills most pathogenic microorganisms or reduces them to a certain extent. In this process, some bacteria or viruses are not destroyed due to resistance to heat or drug force, which has a relative significance. In other words, the disinfectant itself has a certain range of sterilization.

It is not difficult to see that the understanding of the relative and absolute meaning of disinfection and sterilization here is different from our usual understanding. What we usually call "sterilization" should be accurately called "sterilization".

 Part 3  Comparison of common disinfection and sterilization methods 

Disinfection and sterilization, from the mechanism point of view, there are no more than four: dry heat method, wet heat method, drug method, electromagnetic radiation method. From these four basic methods, a variety of disinfection and sterilization methods with different application scopes and application effects are derived.

3.1 Common sterilization methods

Commonly used sterilization methods are: high temperature dry sterilization, high pressure steam sterilization, gas sterilization, filtration sterilization, radiation sterilization and so on.

3.2 Common disinfection methods

Commonly used disinfection methods are: boiling and atmospheric steam disinfection, low temperature disinfection, ultraviolet irradiation disinfection, pharmaceutical disinfection and so on.

 Part 4 Ultraviolet sterilization 

Ultraviolet radiation is a kind of electromagnetic radiation method, which has many applications in local clean workshops, but its effect is limited, because the effect of ultraviolet light is limited, it can not be used to replace chemical disinfection, and ultimately sterilization, and ultraviolet radiation can not be used."

1、Factors influencing the effect of ultraviolet disinfection and sterilization

The factors that affect the effect of ultraviolet disinfection and sterilization are:

（1）Lamp use time: the bactericidal power of the ultraviolet lamp decreases with the increase of the use time, in general, the output power of the ultraviolet lamp after 100h is the rated output power, and the lighting time of the ultraviolet lamp to 70% of the rated power is the average life. The average life of domestic UV lamps is generally about 2000h.

（2）Environmental conditions: Generally, under the conditions of ambient temperature of 20℃ and relative humidity of 40~60%, the sterilization effect of UV lamp is the best. When the temperature is 0℃, the sterilization effect is less than 60%.

（3）Irradiation distance: within 500mm from the center of the lamp, the irradiation intensity is inversely proportional to the distance, and above 500mm, the irradiation intensity is approximately inversely proportional to the square of the distance.

（4）Strain: Because of the membrane structure and shape of the bacteria, the bactericidal effect of ultraviolet light on the strain, that is, the bactericidal rate is also different. If the product of irradiation intensity and irradiation time is assumed to be the irradiation dose, when the required dose of E. coli is 1, staphylococcus, tuberculosis bacillus and the like need about 1~3, subtilis and its spores and yeast and the like need about 4~8, mold about 2 ~ 50.

（5）Installation method: The penetration rate of ultraviolet light is low, which is greatly affected by shielding and installation method. In the biological clean room, there are generally several installation methods of chandeliers, side lights and overhead lights, of which the sterilization effect of overhead lights is the best.

Due to the limitations of ultraviolet sterilization effect and the damage to the human body that may be caused by sterilization, the use of ultraviolet lamps for comprehensive sterilization of biological clean rooms has been rarely used, only individual rooms or local sections such as dressing rooms, laundry rooms, etc. At present, ultraviolet sterilization is commonly used in combination with HVAC system gas phase cycle disinfection.

 2、Gaseous phase cycle disinfection 

Gaseous phase cycle disinfection, is to take some measures, let the air organized circulation through the ultraviolet lamp effective irradiation area, increase the irradiation time and irradiation intensity at the same time, the ultraviolet radiation does not leak hurt, and does not produce ozone, so the ultraviolet lamp can not be turned off to achieve the purpose of circulating air disinfection, disinfection effect is also greatly improved.

 Part 5 Formaldehyde disinfection 

Formaldehyde disinfection is a kind of pharmaceutical disinfection, and is also a common way of biological clean room disinfection. There are two kinds of formaldehyde disinfection: first, on-site disinfection, only a small range of disinfection in the local space of the clean room, formaldehyde can be used directly in the room evaporation (or heating evaporation), the effect is poor, and the detoxification after disinfection is inconvenient. The other is combined with the HVAC system, formaldehyde from the disinfection tank with jacket overflow into the air supply point main pipe of the air conditioning unit and then into the clean room, in order to increase the evaporation intensity of formaldehyde, the disinfection tank jacket through the steam.

It should be noted that because formaldehyde contains trace amounts of formic acid, it has a certain corrosive effect on galvanized air pipes, and it is recommended to use stainless steel pipes.

 Part 6 Ozone disinfection 

Ozone disinfection is a newly developed disinfection method. It is characterized by easy to use, safe, flexible installation and obvious bactericidal disinfection.

Ozone disinfection requires the installation of an ozone generator. The ozone generator can be installed in a variety of ways: desktop, mobile or split type, placed directly in the clean room that needs disinfection; Pipe type, can be installed in the HVAC system's supply and return air main pipe (where the air pipe needs to be expanded); In addition, the ozone generator can also be fixed on the back end of the efficiency filter in the purification air conditioning unit. The latter two installation methods not only disinfect the clean room internally, but also disinfect the air ducts, filters, and internal equipment of the HVAC system.

At present, ozone generators used in clean room disinfection have been produced by a number of domestic manufacturers. The amount of ozone that needs to be consumed when ozone disinfection is used in a biological clean room (or the output of the ozone generator that needs to be selected is the discharge water) can be referred to the relevant manufacturer's information. Compared with formaldehyde disinfection, the advantage of ozone disinfection is that it is easy to install and non-corrosive to air ducts and filtration materials when combined with HVAC systems.

 Part 7 Conclusion 

（1）Disinfection and sterilization are two different concepts.

（2）The choice of disinfection and sterilization method should be determined according to the decoration, equipment and material of the biological clean room, production characteristics, etc., and consider the corrosiveness and economy of the disinfectant, the convenience, safety and the feasibility of GMP verification.

（3）Formaldehyde and ozone are two commonly used disinfection methods. The GMP Certification Guide recommends the use of ozone disinfection.

（4）Either way, it should be used in conjunction with the HVAC system in the clean room. For the residue that is harmful to people after disinfection, it should be diluted to a safe concentration through the ventilation device in time.

（5）Any disinfection methods, disinfectants have a certain degree of resistance, and should be replaced after a period of use.