vol.62-6 (2025/3/31)

Analysis of space cleaning effect using air conditioning air filters

The effectiveness of air filters in air conditioning units for removing indoor pollutants and infectious aerosols was evaluated. A medium performance filter used for general air handling units was replaced with a higher performance air filter, and changes in the concentration of particulate matter in an office were experimentally examined. Furthermore, an infection model based on the material balance was employed to estimate the effectiveness of the air filters’ collection efficiency on the reduction of the risk of infection in the test rooms. The results showed that the use of an air filter with a number-based collection efficiency of 90% was effective in reducing the risk of infection by a significant decrease in the concentration of particulate matter in the room. As a result, a method for determining the appropriate collection efficiency of air filters for air conditioning was proposed.

Decontamination of biosafety cabinets with low-concentration hydrogen peroxide vapor and acetic acid gas

When hydrogen peroxide is used as a decontamination method for microorganisms, there are problems in that it has low permeability and may corrode due to high humidity. However, by combining with gaseous acetic acid, it was found that the decontamination was more effective at a lower concentration than that by hydrogen peroxide alone. The addition of gaseous acetic acid improved the decontamination capacity of hydrogen peroxide, and the decontamination effect of safety cabinets was confirmed even at concentrations as low as several tens of ppm. The decontaminants used in this method are 3% hydrogen peroxide and acetic acid, and it is considered to be a safer method for workers than conventional agents in that it does not handle deleterious substances.

Sterilization of the evaporative humidifier using the plasma treated water

In the biological clean room, microbial contamination of the evaporative humidifier of air handling unit is regarded as important, but the existing countermeasures have many practical problems. Therefore, we investigated a sterilization method for an evaporative humidifier using low-temperature plasma. Recently, sterilization methods using plasma have attracted attention in a wide range of fields. In this paper, we report the characteristic and sterilization effect of plasma treated water made from pure water. In addition, we report the results of studies on applying plasma treated water to prevent infectious diseases.

Calculation and operation of the Carbon Footprint of Product (CFP) for clean equipment

One of the challenges currently facing the world is climate change. In response to this challenge, companies need to make efforts to reduce their emissions of CO₂ and other greenhouse gases (GHG). Recently, an increasing number of companies have been disclosing their carbon footprint of product (CFP) in order to visualize their efforts to reduce GHG emissions and for other purpose. The carbon footprint of product calculates the amount of CO₂ emissions at each stage of the life cycle of a product on a product-by-product basis. In Japan, there are no actual examples of CFP calculated for clean equipment. This paper examines a CFP calculation method for fan filter unit which is clean equipment for industrial use. We have calculated the CO₂ emissions at each stage of the life cycle of fan filter unit and report them.

Studies on the hydrogen gas safe application
(Part 1) Concept of safe application of hydrogen gas and measures on facilities

Hydrogen is expected to be a clean next-generation energy source. Although hydrogen-based technologies such as FCVs are already in the practical stage, hydrogen energy has not yet been fully utilized. One reason for this may be that many people feel the danger of hydrogen gas. Inside FCVs and hydrogen gas supply stations, hydrogen is stored as a highly pressurized gas. Hydrogen gas is indeed extremely flammable and explosive, but if properly managed and operated, it can be used safely like any other fuel. To popularize hydrogen energy, it is important to correctly recognize the dangerous aspects of hydrogen gas and to apply appropriate safety measures. In Part 1, the causes of the accident are analyzed based on the study of past accidents, and the safety measures for the equipment are studied. Next, safety measures for the safe use of hydrogen gas are summarized.

Studies on the hydrogen gas safe application
(Part 2) Experiment and numerical simulation of high-pressure hydrogen-gas leakage

Our attention to hydrogen-gas have been growing as a promising next generation energy source. However, making sure of its use with safety is essential for hydrogen-gas to become used widely. For the application to hydrogen-gas safety, CFD analysis is effective, but high-resolution analysis load is extremely large. Therefore, a numerical method of predicting high-pressure hydrogen-gas dispersion following the leakage from a pinhole as a supersonic jet is developed by CFD with a kinematic jet model as the source of the gas.

Studies on the hydrogen gas safe application
(Part 3) Experiment and numerical simulation of high-pressure hydrogen tank rupture accident

In the safety design of hydrogen related facilities, it is important to understand not only the behaviors of flying objects at the time of the occurrence of high-pressure tank rupture but also the impact on the structure when they collide with a wall. However, little is known regarding the phenomenon of tank rupture. In this study, high-pressure tank rupture experiments were conducted to understand the phenomenon and to obtain data for validation, with the aim of developing an explosion-resistant design method based on numerical analysis for hydrogen-related facilities. Moreover, a reproduction analysis of the experiment using a numerical code was carried out, verifying the accuracy of the tank scattering speed. Furthermore, we performed a reproduction analysis using nonlinear FEM for the high-speed collision phenomenon between flying objects and steel walls accompanying the rupture of a high-pressure hydrogen tank, and confirmed its applicability.

Guideline for the Design, Operation, and Maintenance of Heating, Ventilation, and Air-Conditioning Systems in Healthcare Facilities HEAS 02-2022

The “Guideline for the Design, Operation, and Maintenance of Heating, Ventilation, and Air-Conditioning Systems in Healthcare Facilities” (HEAS 02-2022) has been utilized as Japan’s only guideline for hospital air conditioning systems since its first edition in 1989. This paper outlines the features of the fifth edition, its major revisions, and subsequent developments. The fifth edition has been revamped as a “multi-society guideline” with participation from experts across various fields, and it explicitly indicates the “strength of recommendations” and “quality of evidence” for each recommendation. Additionally, the concept of Infection Control Risk Assessment (ICRA) has been newly introduced, aiming to reduce infection risks during hospital construction projects. Measures for aerosol infection control and alignment with international guidelines have also been strengthened, with plans for an English version publication. Specific revisions include updates to design standards for the Central Sterile Supply Department, ultra-clean operating rooms, and patient rooms for immunocompromised individuals, along with the establishment of new standards for cleanliness and ventilation rates. Notably, the concept of aerosol infection and the WHO-proposed Infectious Respiratory Particles (IRPs) have garnered significant attention, and further revisions based on accumulated knowledge are anticipated in the future.