Yes. Up to fresh air. All war gasses are heavier than air. The better to kill people in trenches and bunkers...
Suspicious Package
A SUSPICIOUS PACKAGE SHUT DOWN PART OF PEACHTREE STREET IN DOWNTOWN ATLANTA THIS MORNING.
THE PACKAGE, WRAPPED IN CHRISTMAS PAPER, WAS FOUND NEAR TRASH CANS IN FRONT OF THE WACHOVIA BANK.
POLICE SHUT DOWN PEACHTREE BETWEEN BAKER AND ELLIS STREETS.
THEY X-RAYED THE PACKAGE AND FOUND IT TO BE EMPTY.
THEY TOOK IT AWAY FOR FURTHER INVESTIGATION.
PEACHTREE STREET IS NOW BACK OPEN AND TRAFFIC IS BACK TO NORMAL.
http://www.wsbtv.com/news/3357629/detail.html
(sorry about the caps, that's how it is at the link)