DENVER (AP) — The U.S. Army wants to change the way it destroys part of its huge stockpile of obsolete chemical weapons in Colorado, but some people worry that could increase the chances of contamination escaping into the air.

The Army's Pueblo Chemical Depot is eradicating 780,000 shells filled with thick liquid mustard agent — many of them dating to the Cold War — under an international treaty banning chemical weapons.

The Army built a highly automated, $4.5 billion plant to do the work, but officials said this week they want to buy two closed detonation chambers for about $30 million each t...