From Bench to Breath: Material Integrity and Performance of Filtering Facepiece Respirators and Surgical Masks After Multi-Cycle Dry-Heat Reprocessing

TL;DR

This study evaluates how dry heat reprocessing affects the durability and performance of respirators and surgical masks over multiple cycles.

Contribution

The study provides a comprehensive assessment of material and performance changes in PPE after multi-cycle dry-heat reprocessing.

Findings

FFR fabrics showed varied responses to thermal stress, with some models stiffening and others softening.

Most treated FFRs met filtration requirements across all cycles, while some surgical masks showed reduced particle filtration efficiency.

Strap materials exhibited model-specific weakening, potentially affecting fit and durability with repeated use.

Abstract

Dry heat inactivates pathogens on personal protective equipment without chemical residues, but its effects on material integrity and performance across multiple reprocessing cycles have not been comprehensively assessed. We evaluated five filtering facepiece respirator (FFR) models and three surgical mask (SM) models after one, two, and three cycles of dry heat (80 °C, 90 min). We measured fabric and strap tensile properties as indicators of mechanical durability [Young’s modulus (E), yield strength (σy), ultimate tensile strength (σUTS), and strain at failure (εf)]. We also assessed particle filtration efficiency (PFE) and airflow resistance (breathability). Under the methods applied herein, all untreated SMs and FFRs performed within the range anticipated for their type. Tensile properties exhibited heterogeneous, model-specific responses to thermal stress. FFR fabrics ranged from progressive stiffening (Dräger DR-X1720C; +120% E) to marked softening (3M-8210; −82% E), while SM fabrics exhibited softening, consistent with thermal relaxation. Straps made of thermoplastic elastomer (3M-8210 and 3M-9320A+) weakened (15–31% σUTS decrease), whereas braided polyisoprene straps (3M-1860S and 3M-1870+) maintained their original strength. Despite these changes, all treated FFR replicates met filtration requirements across all cycles (45/45). For SMs, 24/27 treated replicates met the required PFE threshold (≥98%), but 3 treated RH-S919B replicates fell below this threshold (PFE 94.9% and 97.7% after one cycle, and PFE 97.3% after three cycles), identifying a potential model-specific vulnerability to the treatment. Breathability remained within control ranges for most models; however, the Level 2 ZA-S001B showed decreased breathability (higher airflow resistance) after two (+11.1 Pa) and three (+13.3 Pa) dry-heat cycles, whereas the Level 3 RH-S920TFG showed modest improvements in breathability (lower airflow resistance, up to −10.1 Pa). Under these laboratory conditions, up to three cycles of dry heat at 80 °C for 90 min preserved PFE and breathability in all treated FFR replicates and in most treated SM replicates. Nonetheless, there were measurable, component-specific mechanical changes (especially in some straps) that could compromise fit and durability with repeated use. These findings support dry heat at 80 °C for 90 min as a potential component of emergency PPE processing strategies, provided that model-specific quantitative fit testing and extended-wear studies confirm safe real-world reuse, regulatory approvals are met, and end-user acceptability is considered.

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