Dear Sir, Organizations such as the European Centre for Disease Prevention and Control have challenged the use of valved filtering face-piece respirators (FFPRs) noting that some do not prevent the release of exhaled respiratory particles from the wearer into the environment and may not be appropriate for use as a means of source control in the case of respiratory infections [1]. Naturally, evidence is limited, such as qualitative experiments using fluid flow visualization which 'suggest that FFPR with exhalation valves are not appropriate as a source control strategy' [2]. Agius et al. cite a report which states that 'valved FFPRs reduced exhaled particle emissions to levels similar to or lower than those “exhaled” from surgical masks' [3]. Importantly, the same report cited by Agius et al. states 'the exhalation valve is likely to affect the level of source control provided by a respirator as some particles expelled by wearers may exit through the exhalation valve' [3]; their studies demonstrating a maximum particle penetration of 55% based on a sample of 13 models [3].
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