[Jim E]

Liability Insurance.
Thats a biggie. Is it worth $1500/yr or more for $1M policy to shoot a T-shirt into the stands? I think not!

I've seen industrial accidents happen with stored pressure. They ARE NOT PRETTY. Fortunately, nobody was seriously injured, but the insurance is there for a reason.

For tank safety, there is an aluminum-welded tank on ebay for about $16.00. This should solve that issue. Contact me if interested,for the link.

Of Course the kids-will-be-kids factor is always in play. At my high school, they fired an air cannon after touchdowns. It was located on the flat roof of the announcer's booth just to limit who had access.