A team of researchers recently conducted a systematic review of more than 40 studies regarding reprocessing of filtering facepiece respirators (FFR), including N95s. 

The 42 studies examined 65 mask types. Twenty-seven of the studies evaluated ultraviolet (UV) germicidal irradiation, 19 reviewed vaporized hydrogen peroxide reprocessing, nine moist-heat incubation, 10 microwave-generated steam and seven ethylene oxide. 

At the conclusion of the review, the team observed that UV germicidal irradiation, vaporized hydrogen peroxide, moist heat and microwave-generated steam processing effectively sterilized N95 respirators and retained filtration performance. UV and vaporized hydrogen peroxide methods damaged respirators the least. 

However, vaporized hydrogen peroxide requires longer decontamination periods and is more expensive. Devices for this type of decontamination range from $40,000 to $130,000, according to the researchers. This is compared to methods such as moist-heat incubation, which range in costs from $9,000 to $23,000, or UV, which can cost as little as $40 for a UV-C bulb or between $25,000 to $40,000 for a whole-room decontamination system.

The researchers also found that ethylene oxide may leave toxic residues, and the process is less easily implemented. The sterilant gas with bactericidal, sporicidal and viricidal activity is commonly used in health care for medical equipment and supplies. However, ethylene oxide is a flammable, hazardous gas with known toxic byproducts, which is why the Centers for Disease Control and Prevention recommends against the use of ethylene oxide for personal protective equipment reprocessing because of the potential for harm to the wearer.

The review is a good highlight of methods that hospitals can use to reprocess PPE should the need arise; however, the researchers say further study is needed on decontamination effectiveness for SARS-CoV-2 because few studies specifically examined this pathogen.