In the spring of 2020, as the Covid pandemic was just beginning, a large demand for essential person protective equipment (PPE) exhausted available global supplies.  This was aggravated by increasing needs of frontline clinical healthcare workers, hording of supply by individuals who purchased PPE for their own use, and the lack of manufacturing capacity for PPE.  There was a particularly acute shortage for facemask respirators which were compliant with federal guidelines, often described in the US as N95 masks.

The United States Food and Drug Administration recognized that this was a threat in the face of an uncontrolled and rapidly escalating epidemic, and began to authorize the use of various decontamination techniques to decontaminate used N95 respirators so that they could be re-worn by wearers multiple times.  A number of chemical and physical sanitization techniques were approved by emergency use authorization (EUA), but respirator performance after decontamination was never evaluated. The material in a respirator is a sophisticated and highly engineered fabric that is purposefully designed to capture particles, and it is possible that decontamination could result in damage to that material.  As a result, it was unknown if a decontaminated respirator had similar performance characteristics as a new one.

This project developed a testing platform to assess respirator performance so that various decontaminated respirators could be rapidly evaluated and compared with a new (non-decontaminated) respirator.  Respirators were affixed to a mannequin head that was housed in a closed chamber.  A set of tubes were connected to the chamber, as well as to the ‘mouth’ area of the mannequin.  The chamber was flooded with different sized particles that were generated by combustion of incense, which was housed in a nearby dilution chamber.

We used particle sizing equipment to evaluate the range of sizes and numbers of particles within the chamber, as well as what was able to penetrate through each respirator.  More than 100 different respirators were evaluated, and a number of respirators were found to be damaged and allowed an unacceptable number of particles through the respirator material.  This meant that the respirator was not performing as it was designed, and the decontamination treatment that was used was damaging to the respirator; this placed the wearer at higher risk of infection.

We were able to evaluate respirators that had been decontaminated by vaporized hydrogen peroxide, ultraviolet germicidal irradiation, hydrogen peroxide plasma, dry and wet heat, microwaves, 10% ethanol solution, and diluted household bleach.  In this study, all respirators were ones approved by the US FDA for medical use; our ‘gold standard’ mask was a 1860S model by 3M.  We were also able to evaluate performance of a number of novel face protection devices, including 2- and 4-ply cloth bandanas, KN95 masks (some of which were suspected as counterfeit and had poor performance), and custom facepiece masks with integrated filter cartridges that had been designed by struggling clinical centers.

As a result of this work, it was clear that a number of decontamination treatments damaged respirators; in some cases, EUAs were revoked.  But in contrast, some techniques had little impact of respirator performance, meaning that these decontaminated respirators retained their original performance characteristics; this permitted the re-use of the respirators which both kept wearers safer, but also eased supply chain concerns to ensure adequate PPE availability as the pandemic accelerated.

Last Modified: 06/03/2022
Modified by: Richard E Peltier