The black poly pipe used for gas service is polyethylene, and it usually
handles less than 100 PSI. Polybutylene is crap, and it cost the
original manufacturers $hundreds of millions to settle lawsuits as it
failed in water service lines all over the country. It is initially very
strong and flexible, but with age it loses strength and develops stress
cracks. Go ahead and use PB if you like the idea of digging trenches and
re plumbing everything in a couple of years.

As others have mentioned, using rigid plastic pipes for air service is a
really, really dumb idea born from desperation or ignorance. Spend a
couple of bucks more and use metal tubing.