Valved respirators may be preferable during the covid-19 pandemic

Dear Sir,

After the best possible implementation of engineering and other means of controlling transmission of the SARS-CoV-2 virus, respiratory protective equipment (RPE) plays an important role and it ‘must be appropriate for the specific risks and conditions of use’ [1]. However, to dismiss filtering face-piece respirators (FFPRs) with exhalation valves merely on the grounds that ‘exhaled air is not filtered’ [1] is an unproven assertion [2]. Other devices, besides valved FFPR, by design expel at least a proportion of the air without filtration notably powered air-purifying respirators (PAPRs) and they have also been acknowledged as having a role in the pandemic [1,3,4]. The limited evidence so far does not indicate an increased likelihood of health care cross infection associated with PAPR [3].

Standardized test procedures under laboratory conditions (aerosol mass median aerodynamic diameter of 0.35 microns) have shown that valved FFPRs reduced ‘exhaled’ particle emissions to levels similar to or lower than those ‘exhaled’ from surgical masks, and with an even better differential when compared to unregulated barrier face coverings [5]. Clearly it is not easy to replicate these experiments on subjects infected with covid-19, but the experiments represented the ‘worst-case’ particle penetration, and larger particle sizes (such as ‘droplets’) would be expected to have even less ‘exhalation’ from a valved FFPR than the test aerosol [5]. Since FFPRs are designed with a face seal and intended to be fit tested as well as routinely fit checked, in routine use they leak considerably less ‘unfiltered’ air (in either direction) than surgical masks or unregulated coverings. Because of their inherent design, leakage for all respirators, ‘masks’ and face coverings may be worse on exhaling than inhaling.

A judgement on the most appropriate RPE depends on four factors:

• (1) The likelihood/degree of airborne exposure to the virus

• (2) Physical stressors and other ergonomic considerations: valved FFPRs are more wearable, especially for prolonged periods of use and high work rates [5,6]

• (3) Individual considerations relating to the wearer, such as whether they may suffer from obstructive lung disease [4], and

• (4) In the context of the pandemic, the likelihood that the wearer may be infected.

Especially for workers who may be required to wear RPE for prolonged periods, concerns about comfort and maintaining a consistent fit during a shift may outweigh theoretical advantages of reduced virus emissions from the wearer. Valved respirators may, in specific risk-assessed contexts, provide better protection for the wearers than their unvalved counterparts.