At Turck‘s intrinsic safety seminar hosed by Automated Dynamics, I saw a very good demonstration of how safety barrier devices work: They limit energy to a level that a spark produced will be too weak to ignite the gas surrounding the device it is protecting*. I sat on the front row and took a little video of this in action.
* provided the device doesn’t store energy through capacitance or inductance
After class, I got some bonus footage, a slow-motion video of the explosion.
In this video, you can see the top vent on this special demonstration box pop up quickly when the explosion occurs. You can also see the spark occurring in the bell before the explosion, which is when the energy limiting circuit is turned on. As soon as the energy limiting circuit is turned off, it goes boom.