I've had a 5# CO2 tank pop its pressure valve in my kitchen. It rapidly displaced all of the air in the room in a matter of seconds. Luckily I was in the kitchen at the time and opened all the doors and windows to vent it.
Keep this in mind the next time you refill your 5#, 10# or 20# CO2 tank and throw it in the back of your car. It doesn't matter if you crack the windows, a pressure value relief breach will fill the car with CO2 in seconds.
Another somber story, a friend of a friend was a welder. Took some welding tanks home from a site in his car. They had a slow leak and then next morning when he started the car it detonated. The gas pooled in his car and the ignition was the spark. Killed instantly.
Be very careful with pressurized gasses. I own a pickup and throw everything in the bed and strap it down. If you have a car, even if you put tanks in the trunk, keep your windows open and store the tanks immediately.