In civil air defense engineering, ventilation plugs are only used in the air intake filter room of personnel shelters. The position should be on the air inlet side of the filter absorber, and the height should not be too high, because its function is to reduce the concentration of toxic substances in the filter absorber after replacement, and toxic gases are more important than air. In order to improve ventilation efficiency and shorten ventilation time, ventilation plugs should not be set too high.