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Changes to Step #29

Edit by Guy Kuo

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[title] Fans Tested
[* black] Use a 12 volt blower fan because tubaxial fans usually lack sufficient flow against resistance. We are drawing air in ''through'' a viral filter. Going by just factory spec can be misleading. Those are for static pressure (zero flow) and free air max CFMCFM (zero resistance). We need tomust measure flow rate against HMEF flow resistance.
[* black] Use a 12 volt blower fan because tubaxial fans usually lack sufficient flow against resistance. We are drawing air in ''through'' a viral filter. Going by just factory spec can be misleading. Those are for static pressure (zero flow) and free air max CFMCFM (zero resistance). We need tomust measure flow rate against HMEF flow resistance.
[* black] My original recommended NMB Technlogies BM5115-04W-B50-L00 blower fan with 3.5 CFM (0.098m³/min), static pressure of 0.803 in H2O (200.0 Pa) provided ample airflow (30 L/min at 64 dBA noise) with a single air intake filter and two expiratory flutter valves. . However, this fan is now sold out.
[* black] http://d.digikey.com/HS000xU3ppttIK40NAX00T7 Delta BFB0512HHA-CZMQ has also tested well. It is lower flow but much quieter (20 L/min 55 dBA against HMEF resistance). I have worn this while working in the OR for 11 hours. My EtCO2 at 2 hours was 40 with this Delta fan. Its mounting holes must be slightly enlarged to fit 3 mm bolts.
[* black] San-Ace 109BC12GC7-1 https://www.digikey.com/product-detail/en/sanyo-denki-america-inc/109BC12GC7-1/1688-1035-ND/6191751 is good alternative if user needs higher flow (33 L/min, 60 dBA against HMEF)
[* icon_caution] PLEASE DO NOT HORDE FANS. Only obtain the number you will actually ''deploy'' to providers. Hording deprives others in need during this COVID-19 crisis.
[* black] Other blower fans may yield more ideal combination of power draw, static pressure, flow rate, noise, and availability. 200 to 250 Pa static pressure capability is likely best range.
[* black] If you change fan model, always verify flow rate against HMEF resistance is 20 to 35 L/min. Also measure EtCO2 levels via gas sampling for at least 20 minutes to verify steady state value < 42.