We have been using OSHA’s Hazard Categories from the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) since 2012. I have written a lot about the flammable categories, but I tend to get a lot of questions about the Health Hazard Categories in my HAZCOM and HAZMAT training so I thought I would explain in real-world terms how toxic some chemicals are using the new GHS categories. In this article, I will cover the most common route of entry: Inhalation of GASES