A：The wind speed of HEPA in equipment area of tunnel clean room should preferably be taken 0.4~0.5m/s, and that of walkway area should preferably be taken 0.25~0.35m/s, then air flow in equipment area will diffuse into walkway area to ensure effect of unidirectional flow and cleanliness in equipment area. To gain different wind speed in equipment area and walkway area, keep to the following method:
a. If section area (A) is equivalent, decrease in air intake in walkway area is permissible, then air outlet speed decreases naturally （∴Q=AV）, together with lower class of cleanliness.
b. Non-unidirectional flow is adopted in walkway area, but air outlet should be kept away from working area to avoid turbulent flow by air outlet, and resultant degradation of cleanliness in working area.