Front fork compression adjuster .... under pressure?

Hi all,

Silly question showing my ignorance, but I'd still like to know....

I will be swapping my front end for a 2006 USD Benelli/Marzocchi set of forks and have a question about the compression adjuster at the bottom of the forks.

I was trying to key the bottom section to re-paint and tried to take off the compression adjuster hex bolt with internal screw.

But as I was unscrewing it, air/gas started to come out..?

Are these under pressure? What from? How do I re-pressurise (if needed)?

Paul