Feasibility and Requirements

A Helmet Type Mask "Distancing-Free Mask": An Engineering Solution that Eliminates the Lockdown
Y. Fujii, A. Takita, S. Hashimoto — Journal of Mechanical and Electrical Intelligent System, Vol.3, No.3, pp.1–7, 2020.
https://jmeis.e-jikei.org/issue/archives/vol03_no03/F001/Camera_ready_manuscript_JMEIS_F001_535362_final.pdf

Role: Concept and engineering starting point

The first paper, proposing the helmet-type “Distancing-Free Mask” as an engineering solution that makes lockdown unnecessary.

An Engineering Alternative to Lockdown During COVID-19 and Other Airborne Infectious Disease Pandemics: Feasibility Study
Y. Fujii — JMIR Biomedical Engineering, Vol.9, e54666, 2024.
https://doi.org/10.2196/54666

Role: Feasibility of PAPRs for the general public

Examines whether mass production and distribution of affordable, comfortable, high-performance PAPRs could let a country avoid lockdown in an airborne pandemic.

• An alternative to lockdown: PAPRs reduce airborne and droplet transmission and lower the probability of infection per contact. The paper proposes a social system in which stay-at-home requests and curfews are replaced by permission to go out while wearing a PAPR.
• Seven areas for improvement: flow optimisation, precise differential-pressure control, design, maintenance, variants for different uses (such as booth types), information-terminal functions, and performance evaluation.
• IoT management of wearing rates: a network that tracks each person's wearing rate, balancing government infection control with personal freedom (implemented in Chapter 5).
• Figures: PAPR air supply is about 200–400 L/min (resting breathing about 6–10 L/min). Parts for a simple prototype cost about US$40; a prototype with a controller about US$300.

Examination of the requirements for powered air-purifying respirator (PAPR) utilization as an alternative to lockdown
Y. Fujii — Scientific Reports, Vol.15, 1217, 2025.
https://doi.org/10.1038/s41598-024-82348-0

Role: Conditions for population-level infection control

Calculates, with a simple model considering only airborne and droplet transmission, how many people need to wear PAPRs to control an epidemic.

• Model: Rt_target = [1 − Wr × Ir_in] × Rt (Wr: wearing rate; Ir_in: supply-side infection reduction).
• Required wearing rate (Rt = 2, perfect supply-side shielding): about 50% continuous wear for Rt = 1.0, about 55% for 0.9, about 75% for 0.5.
• If everyone wears one: a supply-side reduction of about 55% is enough to bring Rt from 2 to 0.9.

These are calculations from an idealised model, not measurements. They lead to the proposal in Chapter 6 that required performance should not be fixed at APF 1000 for all purposes, but determined empirically from the pathogen, exposure time, wearing rate and adherence.