Disinfection and sterilization represent two distinct concepts in cleanroom contamination control. This article compares common disinfection and sterilization methods utilized in biological clean rooms, examining three primary techniques: ultraviolet sterilization, formaldehyde fumigation, and ozone disinfection. Keywords: UV, formaldehyde, ozone disinfection.

1、Introduction

According to research data, the human body carries approximately 1 to 104 kinds of bacteria per 6 to 7 square centimeters of skin, about 1% of which are pathogenic, while normal breathing and speaking also release bacteria. Consequently, preventing bacterial contamination and eliminating microorganisms in clean rooms—particularly facilities with strict cleanliness classifications—is critical. Disinfection and sterilization serve as two proven methods to destroy bacteria and satisfy microbiological control standards in biological clean rooms.

2、disinfection and sterilization are two different concepts

Disinfection and sterilization are two fundamentally different concepts. Sterilization refers to killing or removing all microorganisms (including bacteria, viruses, etc.) within or on a substance, carrying an absolute meaning. In other words, an article is either completely sterilized or not sterilized at all, leaving no intermediate state of partial sterilization. In practical cleanroom applications, absolute sterilization is virtually nonexistent because achieving complete microbial eradication requires an infinitely long processing time.

Disinfection, by contrast, is the process of eliminating most pathogenic microorganisms or reducing their count to an acceptable level. During disinfection, certain bacteria or viruses may survive due to thermal or chemical resistance, giving disinfection a relative rather than absolute significance. Consequently, each chemical disinfectant or disinfection method has a defined antimicrobial efficacy range.

It is not difficult to see that the relative and absolute definitions of disinfection and sterilization differ from everyday usage. What is commonly termed \"sterilization\", to be precise, should strictly be termed \"sterilization.\"

3、common methods of disinfection and sterilization

From a mechanistic perspective, disinfection and sterilization methods fall into four fundamental categories: the dry heat method, the damp heat method, chemical or drug methods, and the electromagnetic radiation method. From these four core mechanisms, a variety of disinfection and sterilization techniques with diverse application scopes and performance characteristics are derived.

3.1 Common sterilization methods

Commonly used sterilization methods include high-temperature dry heat sterilization, high-pressure steam sterilization, gas sterilization, filtration sterilization, radiation sterilization, and related techniques.

3.2 Commonly used disinfection methods include boiling and atmospheric steam sterilization, low-temperature disinfection, ultraviolet radiation disinfection, pharmaceutical disinfection, and similar approaches.

4、ultraviolet sterilization

Ultraviolet radiation is an electromagnetic radiation method widely utilized in localized cleanroom workshops, though its efficacy has recognized limitations. The WHO GMP guidelines (1992 edition) expressly state: \"Because of the limited effect of ultraviolet light, it should not be used instead of chemistry. Disinfection.\" Furthermore, Article 17.65 states: \"Final sterilization, UV irradiation cannot be used.\"

4.1 Factors affecting the effectiveness of UV disinfection and sterilization

The key factors that affect the effectiveness of UV disinfection include:

(1) Lamp use time: The germicidal efficacy of a UV lamp decreases as operating time increases. Generally, the output power achieved after 100h of UV lamp operation represents its rated output power, and the operating duration until output drops to 70% of rated power defines its average service life. The average lifespan of domestic UV lamps is typically around 2000h.

(2) Environmental conditions: Generally, ultraviolet lamps achieve optimal sterilization performance at an ambient temperature of 20 ° C and a relative humidity of 40 to 60%. When the ambient temperature falls to 0 ° C, the resulting sterilization efficiency is less than 60%.

(3) Irradiation distance: Within 500mm from the tube center, the intensity of illumination is inversely proportional to the distance, whereas beyond 500mm, illumination intensity becomes approximately inversely proportional to the square of the distance.

(4) Species: Due to variations in cell membrane structure and morphology, the bactericidal effect of ultraviolet radiation differs among microbial strains. Assuming the irradiation dose is defined as the product of irradiation intensity and exposure time, taking the required dose for Escherichia coli as 1, Staphylococcus, Mycobacterium tuberculosis, and similar strains require approximately 1 to 3, Bacillus subtilis along with its spores and yeasts require 4~8, and mold requires about 2~50.

(5) Installation method: Ultraviolet light exhibits low penetration capability and is significantly influenced by shadowing and mounting methods. Within a biological clean room, standard installation options include chandeliers, side lamps, and ceiling lamps, with ceiling lamps delivering the most effective sterilization results.

Due to the limitations of ultraviolet sterilization coverage and the potential health hazards to humans during operation, ultraviolet lamps alone are rarely used to sterilize an entire biological clean room. Their application is generally limited to dedicated spaces such as locker rooms and laundry rooms. Currently, ultraviolet disinfection is commonly integrated with HVAC systems to perform gas phase circulation sterilization.

4.2 gas phase cycle disinfection

Gas phase circulation disinfection systematically directs airflow through the effective irradiation zone of ultraviolet lamps. By increasing exposure time and radiation intensity without UV leakage to personnel or ozone generation, the UV lamps can operate continuously without shutdown, significantly boosting overall disinfection performance.

5、formaldehyde disinfection

Formaldehyde disinfection is a chemical sterilization technique widely utilized for biological clean rooms. It is primarily implemented in two ways: localized on-site disinfection, which treats only limited cleanroom zones through direct indoor evaporation (or heated evaporation) with lower efficiency and difficult post-disinfection detoxification; and HVAC-integrated disinfection, where formaldehyde vapor from a jacketed disinfection tank enters the air conditioning supply unit to be distributed into the clean room, utilizing steam inside the tank jacket to accelerate formaldehyde evaporation.

It should be noted that because formaldehyde contains substantial quantities of formic acid that corrode galvanized air ducts, utilizing stainless steel tubes is recommended.

6、ozone disinfection

Ozone disinfection is an advanced cleanroom disinfection method offering significant advantages, including convenient operation, high safety, flexible installation, and proven bactericidal effectiveness.

Ozone disinfection requires the installation of an ozone generator, which supports multiple configurations: standalone desktop, mobile, or split units placed directly inside the target cleanroom; ducted models integrated into the HVAC system's return air mains (where duct expansion is required); or fixed units positioned at the rear of the air handling unit's high-efficiency filter. These latter two installation methods disinfect the cleanroom interior while simultaneously sanitizing the HVAC system's air ducts, filters, and internal equipment.

Currently, ozone generators for cleanroom disinfection are widely produced by numerous manufacturers in China. Cleanroom operators can consult relevant manufacturer specifications to determine ozone consumption requirements for biological cleanrooms (or equipment sizing for water discharge applications). Compared with formaldehyde fumigation, ozone disinfection offers simpler installation and remains non-corrosive to air ducts and filtration media when integrated with the HVAC system.

7、conclusion

(1) Disinfection and sterilization represent two distinct contamination control concepts.

(2) Selecting disinfection and sterilization methods should be based on biological cleanroom finishes, equipment, and materials, production characteristics, disinfectant corrosiveness, cost-efficiency, operational convenience, and safety, while comprehensively determining the feasibility of GMP validation.

(3) Formaldehyde and ozone are two commonly utilized cleanroom disinfection methods, with ozone disinfection specifically recommended in the GMP Validation Guide.

(4) In all cases, disinfection should be operated in conjunction with the cleanroom HVAC system. Any residual gases harmful to personnel after disinfection must be diluted to safe exposure concentrations through proper ventilation.

(5) Microorganisms can develop resistance to any disinfection method or chemical disinfectant, requiring routine rotation and replacement after periodic use.