Regeneration Cyle
The regen cycle simply dumps fuel into the exhaust to heat up the particulate filter to burn off the accumulated particulate matter. For the most part it's a seamless action. The only time you'll ever notice it is in park when it will idle up to around 800-1000 RPM and the exhaust will be hot as hell.
As for dangerous, maybe. You'd have to park really close to something though. I've held some plastic wrappers off IV bags up to it and they melt pretty fast. (It's a pretty thick wrapper)
The one bad thing about regens is that they use fuel-a lot of fuel. I've seen the MPG meter drop almost 1MPG after a regen in park.
Also the 6.4 uses a lot of fuel anyway so keep that in mind.
Mike



