Contamination travels along routes, not only through doorways
Transfer does not always begin at the main entrance. It may start in goods receiving, a warehouse route, an outdoor loading area, a transition toward production, an AGV/AMR route, a pedestrian route or the entrance to a cleanroom or hygiene-sensitive area.
The useful signals appear along the route: floor marks, dust carried toward production, moisture in the wrong place, particles or audit observations associated with the same crossing.