Lack of engineering control to arrest accidental back-flow (Design).
防止意外回流缺乏工程控制(设计)。
2
The change of back-flow pressure, deformed exhaust hole, pre-inflow structure and so on can be adopted to reduce back-flow impact.
根据回流压力的变化规律，采取异型排气口、预进气结构等措施减小回流冲击。
3
Blocking checkpoints occur if we don't process the things efficiently on secondary, and the problem in secondary will back-flow and impact primary (blocks primary).