Let’s start with the “smallest” issue. What’s the smallest size human naked eye can see? Have you ever thought about how the manufactures promise the vaccine that inject into your body is particle free? According to USP1790, for 50um particle, the chances to detected by human eye is, 0%. For 100um, chances raised to 70%; for 150um, it raised to over 95%. However, there’s no need to be scared as the visual inspection regulation and techniques are improving. One automatic inspection machine now is able to detect particles below 50um.

Picture Reference from Cleanroom technology