What makes a gas a flammable gas?

With all the chatter these past few weeks about flammable gases and their NFPA 704 Diamond “Degree of Hazard”, it was suggested by several SAFTENG members that I write an article explaining what a “flammable gas” actually is, as some of our group text indicate some may not fully understand the true hazard of working with/around a liquified pressurized gas.  So here we go…

First thing is to establish what a “gas” actually is.  Keeping this simple, we know we have three (3) states of matter:

1. Solid
2. Liquid
3. Gas

Gas is a state matter that is in that state at the Standard Temperature and Pressure (STP), which is 68°F and 14.7 psi.  In other words, the material wants to naturally be a gas and this means it will have a boiling point <68°F at 14.7 psia.   

There are three major groups of gases:

1. Liquefied [Pressurized] Gases
2. Non-Liquefied Gases (commonly called a “compressed gas”)
3. Dissolved Gases