The Army yesterday said it is monitoring air quality during a controlled burn at a Schofield Barracks target range this week in response to concerns that the fires could put fine particles of depleted uranium in the air.

The prescribed burn in 1,100 acres of munitions impact area is being done to minimize the chance of brushfires and to prepare the area for testing for the presence of depleted uranium.

A 1960s Army nuclear weapon system called the Davy Crockett used aiming rounds that contained depleted uranium, or DU, at Schofield and possibly Makua Valley and Pohakuloa Training Area on the Big Island.

The Army was unaware of the presence of the weakly radioactive element until a contractor removing unexploded ordnance for the Stryker brigade discovered it in 2005 at Schofield.

The find touched off worry, particularly by some Big Island residents living downwind from Pohakuloa, that fine particulate DU could be whipped up by winds or training and cause lung injury if inhaled.

Connecticut contractor Cabrera Services is scheduled to conduct surveys for the heavy metal Aug. 13 to 19 at Makua and at Pohakuloa, and field work is scheduled at Schofield Aug. 13 through Sept. 28.

Responding to public concerns, the Army had Cabrera Services conduct a reference burn on July 12 and a test burn on July 13 at the 1,100-acre ordnance impact area north of Kolekole and Trimble roads on Schofield.

The Army said the reference burn was conducted on a one-acre site where DU was not present to establish a baseline.

The test burn was conducted on a one-acre area where DU was present. Air monitors detected no DU health hazard from the burn and accompanying smoke, the Army said.

The Army said it burned 350 to 400 acres yesterday, and will try to burn the remainder of the 1,100 acres this week.

Air monitor samples will be sent to an independent lab for analysis, and the results won't be available for several weeks, but the Army pointed to the test burn results in going ahead with the larger burn.

In January 2006, the Army confirmed it had found 15 tailfin assemblies that contained DU at the Schofield range. The DU was used in aiming rounds that simulated the trajectory of the Davy Crockett, a weapon that could fire a 76-pound nuclear bomb.

Tad Davis, deputy assistant secretary of the Army for the environment, sent a letter in July to U.S. Sen. Daniel K. Inouye, D-Hawai'i, saying, "The U.S. Army, working with state and federal agencies, intends to conduct a full evaluation of the potential for additional DU residue from the XM 101 Davy Crockett spotter round to be present on Army ranges. We are working closely with the Hawai'i Department of Health and the Nuclear Regulatory Commission to help ensure that the people of Hawai'i will have confidence in any steps taken to address this concern."

Shannon Rudolph, a Big Island resident, obtained the letter after contacting Inouye's office about DU concerns.

"I'm really worried about that (the controlled burn on O'ahu), even though I don't live there," Rudolph said yesterday. "I'm worried for all of those people who are downwind."

A state health official said the real danger with depleted uranium comes with fine particulate, which can be spread by wind and stick to the cells of the lung.

But according to the World Health Organization, "very large amounts of dust" would have to be inhaled for there to be an additional risk of lung cancer.

The amount of DU present is also likely to be small, and state testing in May found normal radiation levels in the air near Pohakuloa Training Area on the Big Island.

Reach William Cole at wcole@honoluluadvertiser.com.