Page 4 - Bow Tie for understanding COVID-19

But Barriers Degrade

100% perfect physical separation will stop all infections, but things degrade this perfection, so we have
government guidance (or “controls”) to try and minimise the holes developing in the barriers. If the
controls work perfectly then the barrier will continue to work.

So the Self Isolation barrier, which physically separates me from infected people can fail due to two
main degradation factors:

PPE (masks and screens) as an effective barrier can degrade due to unavailability, people not knowing
how to use them, etc. but this would probably need its own bow tie.