Figure 1
![Figure 1](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2F1880-5981-66-102/MediaObjects/40623_2014_Article_91_Fig1_HTML.jpg)
Backscattered electron images of category 3 particles. White bars show 50 μm. Particles allocated to the first and second examinations are shown in the top and middle rows of the figure. RA-QD02-0190 is classified as fibrous type (type 2), and RB-QD04-0001 and RB-CV-0055 are classified as faint type (type 3).