Effects of Various Physical and Chemical Disinfection Methods on the Fine Particle Collection Efficiency of N95 Respirators and Surgical Masks.

Several studies have reported on the effectiveness of various disinfection methods for severe acute respiratory syndrome coronavirus 2 and their applicability to the disinfection of N95 respirators and surgical masks. To date, there have been no reports on the decontamination of deep in the intermediate layers of the multilayered structure. In this study, the conditions required for decontamination of such layers were simulated by considering the thickness and shape of N95 respirators or surgical masks (samples). After applying heat (steam, dry heat, or hot water) at 75°C for 60 min or chemical (benzalkonium chloride or laundry detergent) treatment, the collection efficiency of the samples was evaluated. Following the dry heat treatment, the time between the treatment and heat reaching the intermediate layer of the filter fiber was extended by 10 min. A dry heat disinfection method that combines hot water and a closed container was also evaluated, and satisfactory conditions were extended by 60 min. For each heat treatment, there was almost no effect on the collection efficiency, although there were cases where deformation was caused by mechanical stress. In contrast, chemical treatment resulted in a reduction in the collection efficiency of smaller particles.

Assessment of Capacity to Capture DNA Aerosols by Clean Filters for Molecular Biology Experiments.

Experimental contamination by exogenous DNA is a major issue in molecular biological studies for data quality and its management. We herein assessed DNA aerosols for the risk of contamination and tested the capacity of clean air filters to trap and remove DNA aerosols. DNA aerosols were generated by atomizing a DNA solution and introduced into a laminar flow clean air unit. Capture and detection performed upstream and downstream of the clean air unit showed that a significant fraction (>99.96%) of introduced molecules was trapped and removed by the filter. Although DNA aerosols appear to be an avoidable source of exogenous contamination, a clearer understanding and careful experimental procedures are needed in order to perform contamination-free, high-quality molecular biology experiments.

Breathing simulator of workers for respirator performance test.

Breathing machines are widely used to evaluate respirator performance but they are capable of generating only limited air flow patterns, such as, sine, triangular and square waves. In order to evaluate the respirator performance in practical use, it is desirable to test the respirator using the actual breathing patterns of wearers. However, it has been a difficult task for a breathing machine to generate such complicated flow patterns, since the human respiratory volume changes depending on the human activities and workload. In this study, we have developed an electromechanical breathing simulator and a respiration sampling device to record and reproduce worker's respiration. It is capable of generating various flow patterns by inputting breathing pattern signals recorded by a computer, as well as the fixed air flow patterns. The device is equipped with a self-control program to compensate the difference in inhalation and exhalation volume and the measurement errors on the breathing flow rate. The system was successfully applied to record the breathing patterns of workers engaging in welding and reproduced the breathing patterns.