Русский: Иллюстрация из технического отчёта NIOSH, работа правительства США, является общественным достоянием (in the public domain).
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Technical Report. Filtering Facepiece Respirators with an Exhalation Valve: Measurements of Filtration Efficiency to Evaluate Their Potential for Source Control
Uploaded a work by Portnoff L, Schall J, Brannen J, Suhon N, Strickland K, Meyers J. from Technical Report. Filtering Facepiece Respirators with an Exhalation Valve: Measurements of Filtration Efficiency to Evaluate Their Potential for Source Control https://www.cdc.gov/niosh/docs/2021-107/ with UploadWizard