Microwave- and heat-based decontamination of N95 filtering facepiece respirators: a systematic review

Abstract

Background: In pandemics such as COVID-19, shortages of personal protective equipment are common. One solution may be to decontaminate equipment such as facemasks for reuse.

Aim: To collect and synthesize existing information on decontamination of N95 filtering facepiece respirators (FFRs) using microwave and heat-based treatments, with special attention to impacts on mask function (aerosol penetration, airflow resistance), fit, and physical traits.

Methods: A systematic review (PROSPERO CRD42020177036) of literature available from Medline, Embase, Global Health, and other sources was conducted. Records were screened independently by two reviewers, and data was extracted from studies that reported on effects of microwave- or heat-based decontamination on N95 FFR performance, fit, physical traits, and/or reductions in microbial load.

Findings: Thirteen studies were included that used dry/moist microwave irradiation, heat, or autoclaving. All treatment types reduced pathogen load by a log₁₀ reduction factor of at least three when applied for sufficient duration (>30 s microwave, >60 min dry heat), with most studies assessing viral pathogens. Mask function (aerosol penetration <5% and airflow resistance <25 mmH₂O) was preserved after all treatments except autoclaving. Fit was maintained for most N95 models, though all treatment types caused observable physical damage to at least one model.

Conclusions: Microwave irradiation and heat may be safe and effective viral decontamination options for N95 FFR reuse during critical shortages. The evidence does not support autoclaving or high-heat (>90°C) approaches. Physical degradation may be an issue for certain mask models, and more real-world evidence on fit is needed.

Keywords: COVID-19; Decontamination; Filtering facepiece respirator; N95; Pandemic; Personal protective equipment.

Figure 1

PRISMA flow diagram of search and screening process.

Figure 2

Impact of microwave and heat decontamination interventions on aerosol penetration through N95 filtering facepiece respirators. Treatment replicates are denoted by n. Horizontal axis and effect sizes represent the differences in percentage aerosol penetration between untreated and treated masks. Within-study data for different masks and treatment parameters are averaged to yield a single effect size. Results are only depicted for studies that used National Institute for Occupational Safety and Health certification testing procedures. RE, random effects.

Figure 3

Impact of microwave and heat decontamination interventions on airflow resistance (pressure drop) of N95 filtering facepiece respirators. Treatment replicates are denoted by n. Horizonal axis and effect sizes represent the differences in airflow resistance between untreated and treated masks, expressed in mmH₂O. Within-study data for different masks and treatment parameters are averaged to yield a single effect size.

Figure 4

Germicidal effect of microwave and heat decontamination interventions on viral pathogens. Treatment replicates are denoted by n. Horizontal axis and effect sizes represent log₁₀ viral reduction factors between untreated and treated masks. Within-study data for different masks and treatment parameters are averaged to yield a single effect size for all studies except Fisher et al. (2009), which was divided into two time ranges due to a significant increase in germicidal effect after the 30-s timepoint. Bactericidal measurements are not shown.