5 ring dust combustion
By U.S. National Institute for Occupational Safety and Health – Building a Safety Program to Protect the Nanotechnology Workforce: A Guide for Small to Medium-Sized Enterprises (in en-us). U.S. National Institute for Occupational Safety and Health p. 17 (March 2016). Retrieved on 2017-03-05., Public Domain, https://commons.wikimedia.org/w/index.php?curid=57176370