This week I was more than surprised to learn that not everyone uses the most up-to-date NIOSH IDLH values when deciding on their respiratory protection needs. This was brought to my attention after a SAFTENG member contacted me about my 2012 article “What type of respirator do I need?”. This safety professional had downloaded a document from one of, if not the the top, respirator companies in the world and began working through the Maximum Use Concentration (MUC) formula to determine the type of respirator his/her employees would need to be wearing to be adequately protected. When he/she was done they noticed their numbers differed from those I used in my worked examples in my article. When I responded that Chlorine’s IDLH is not 30 ppm, that it is 10 ppm you can imagine their confusion.