This paper explains the basic knowledge necessary for successful decontamination from the viewpoint of “microbial decontamination agent selection”. By chemically understanding the characteristics of the decontamination agent, it is possible to select a decontamination method according to the purpose and calculate the time required such as the timing of connection to the next step after decontamination. In particular, oxidizing decontaminants such as chlorine dioxide, hydrogen peroxide, and peracetic acid discussed in this paper have similar sterilization mechanisms, but their properties as decontamination agents are completely different. Therefore, if the choice is made incorrectly, problems may arise in terms of decontamination safety, effectiveness, impact on products, etc. In order to avoid such risks, I would like you to understand “decontamination agents” from a scientific perspective and adopt decontamination methods according to the environment.

View full abstract

Hydrogen peroxide gas is used in the decontamination and sterilization of various types of equipment and various environments. By performing the so-called “dry process” using a gas concentration monitor, many guidelines can be met and effective decontamination and sterilization can be achieved. A wide range of damage can be avoided through the prevention of condensation within the target space, including surface condensation.

View full abstract

Formaldehyde has been the most commonly used for a space biological decontaminating agent because of its efficiency and convenience. Traditional fumigation with formaldehyde may be still effective method, but the use of formaldehyde has been strictly regulated by authorities for some years. Hydrogen peroxide （H₂O₂）has a powerful oxidizability and has become an alternative agent to formaldehyde for biological decontamination. Since the catalyst decomposes H₂O₂ to water and oxygen at the end, it is good for reduction of environmental burdens. Furthermore, four other types of gasses can be decomposed with the catalyst. This is an introduction of catalyst which reacts on multiple type of gasses.

View full abstract

Peracetic acid（ PAA） is a strong oxidant with excellent sporicidal, microbicidal, fungicidal and virucidal activities. It is effective even at low concentrations and has excellent biodegradability. Dry fogging fumigation with PAA is effective for decontaminating indoor spaces such as laboratories, biological cleanrooms, and is widely used mainly in Europe and North America. On the other hand, condensation due to an unintentional excessive increase in relative humidity during fumigation may cause corrosion of metals, equipment failure and residual odor. The PAA Cycle Decontamination （PACD） system eliminates the risk of unintentional condensation by keeping the relative humidity below 75%. By repeating the cycle of spraying with a fogger and recovery（ collecting） with a dehumidifier during the decontamination time, it is possible to continuously supply PAA gas（ PAA gas can be continuously supplied） while maintaining a constant humidity. This also enables decontamination even when the room temperature is low or the initial humidity is high, without adjusting temperature and humidity conditions in advance. Vaporized PAA passes through a HEPA filter, allowing decontamination of biosafety cabinets. The PACD system greatly expands the possibilities of PAA decontamination.

View full abstract

The sterilization ability of the chlorine dioxide（ ClO₂） gas, which has been used as an alternative decontamination agent of carcinogenic formaldehyde gas, is investigated. The validity of the sterilization condition based on a 60 m3 actual production line of clinical experimental medicine is evaluated. As the result, all of the 42 BIs （biological indicators） in the production line were negative. In addition, the fast and reliable decision protocol by a Micro Colony-ATP （Adenosine Triphosphate） method as an alternative method to the culture and measurement method（ gas measurement method, plate culture method）of BI bacteria, which took several days to several weeks for decontamination judgment is devised and validated. As the result, we confirmed that the judging decontamination effect was possible within 12 hours. The combination of chlorine dioxide gas decontamination and the Micro Colony - ATP method can further increase the convenience of users of decontaminated facilities because the decontamination judgment result can be confirmed, and the operation can be started by the next morning after the decontamination work.

View full abstract

Biological decontamination is difficult to control and replicate. Under these circumstances, biological decontamination with chlorine dioxide gas is currently used in small spaces. We have tested chlorine dioxide gas in small spaces and found chlorine dioxide to be easy to control and reproducible. The potential for application in larger spaces is also to be discussed.

View full abstract

For COVID-19 and for many other respiratory viruses three transmission routes are dominant; （1）combined droplet and airborne transmission in 1-2 m close contact region;（2） long-range airborne（ aerosol-based） transmission; and（3） surface （fomite） contact through hand-hand, hand-surface, etc. contacts. The risk of an airborne transmission and cross-infection over distances more than 1.5 m from an infected person of this（2） can be reduced with adequate ventilation and effective air distribution solutions. It is at this distance that ventilation may be able to control the infection. This report explains the operation method of the mechanical ventilation system and the points of ventilation design. The scope is limited to commercial and public buildings. Residential buildings are out of the scope of this report. The most effective operation method that can be dealt with is the improvement of the performance of the air filter. On the other hand, in the design of building services, high-efficiency ventilation systems and heat recovery equipment can be considered other than the increase in outdoor air volume. Also, this is a basic thing, but it is important to design supply air inlets and exhaust air outlets so as not to create a staying of an air.

View full abstract