Under the COVID-19 pandemic, many types of masks for particulate matters are used at hospital wards and public spaces over the world. These masks are based on air filtration of aerosol particles but the shapes and the performances run the whole gamut. In this topic, the general features of these masks, such as the requirements of dust respirator in national standards, the collection mechanisms of aerosol particle by air filter, and the fit test for the respirators, are stated. The authorized masks in Japanese market have enough filtration performance but the suitable selection and the decent use of these masks for each wearer are apt to be neglected. The fit tests of mask and the face of wearer are explained for better respiratory protection.

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With the spread of COVID-19, respiratory protective devices are becoming more important as a means of preventing infection. Since the performance of respiratory protection mainly depends on how well the protection fits the wearer, it is important to quantitatively evaluate whether the protection is properly worn. The method of evaluating whether or not protective equipment is properly worn is called the fit test, and has been regulated by OSHA since 1998 in the respiratory protection standard（ 29 CFR 1910.134）. In 2019, a shortened protocol will be adopted that enables faster evaluation when using a fit test instrument by Condensation Particle Counter （CPC）. The CPC method is the mainstream of measurement method for quantitative fit test instrument, and we have developed AccuFIT9000 which is a fit test instrument by CPC in Japan. As a result of comparative evaluation with Porta Count according to ANSI standard（ Z88.10-2010 Annex A2）,it has shown that AccuFIT 9000 has sufficient performance for fit test. We have also shown that AccuFIT9000 PRO can perform the accurate fit tests for N95 mask. Regulations on respiratory protection have tended to be stricter in recent years, and fit test instrument is expected to become even more important in the future.

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The N95 is a type of particulate respirators certified by the US National Institute for Occupational Safety and Health （NIOSH）. On the other hand, the DS2 respirator is the device that conforms Japanese standard for dust respirators prescribed by the Ministry of Health, Labor and Welfare, and has the same performance as the N95 respirator. Respirators are personal protective devices which used to prevent respiratory diseases caused by inhalation of hazardous particulate matter suspended in the working environment, unlike masks for the public such as surgical masks. Although the N95 and DS2 respirators are also effective for minimizing the risk of infection in the medical facilities, proper selection and training are required to ensure respiratory protection while wearing them. This is because the fit between the wearer’s face and the respirator facepiece is important for the protective performance in the actual use. In the United States, workers are required to perform pre-work and annual fit tests. It is thought that in Japan as well, the spread of fit tests and seal checks will enable more effective respiratory protection.

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Nonwoven fabric sheet is usually used as mask due to the comparatively high particles removal performance and ease of breathing. Our main purpose is to develop the novel masking material which can remove as much SARS-CoV-2 as possible. The diameter of the SARS-CoV-2 is considered to be about 50nm to 150 nm which is a size that can be removed by the nonwoven fabric sheet mask according to the particle collection air filter mechanism （FM）. The most disturbing problems are that large amounts of aerosols of various sizes, including many viruses, are released from the mouth by coughing, and those around the diameter of 300nm slip through the mask according to the FM. In order to solve the problem, the electric charge is usually given to the mask. Such modification, however, loses the effectiveness in the presence of water molecules from the mouth. In general, the mask performance is represented by the particle filtration efficiency （PFE） and pressure drop （PD） similar to an air filter. PFE corresponds to a measure of virus protection and PD to ease of breathing. Therefore, better performing masks have higher PFE and lower PD. Z-nanofiber sheet mask developed by using Z-melt spinning method of polypropylene （PP） could solve the problems in charged masks, because the nanofiber can detect the aerosol around 300nm diameter without giving electric charge. Moreover, it has another advantage that is increase of PFE in keeping PD constant after washing or autoclave treatment. It is suggested that the Z-nanofiber sheet mask shows the best performance to the protection of SARS-CoV-2.

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This paper describes decontamination of the environmental surface of an unmanned room by chlorine dioxide gas. Chlorine dioxide gas is harmful to the human body, so for safety, it is necessary to be careful not to leak it from the target room. In addition, since chlorine dioxide is corrosive, it is also necessary to consider protecting or evacuating indoor articles. Because there is a trade-off between the decontamination effect of chlorine dioxide and the damage caused by corrosion, it is necessary to determine the decontamination conditions （gas concentration, humidity, treatment time） in consideration of both. Furthermore, in order to obtain a sufficient decontamination effect, it is necessary to devise a method to make the entire room uniform at a predetermined gas concentration.

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