The Army yesterday downplayed the possible health risk of depleted uranium as it continues to assess levels found at military training ranges on O'ahu and the Big Island, saying the weak radioactive material is isolated at target sites.

The heavy metal was used in aiming, or "spotting" rounds for a 1960s weapon system called the Davy Crockett that could fire a 76-pound nuclear bomb.

A panel of experts representing local, state, national and federal agencies gathered at Schofield Barracks yesterday to discuss depleted uranium use in Hawai'i.

"The Army takes very seriously its roles and responsibilities with regards to this discovery," said Col. Matthew Margotta, commander of U.S. Army Garrison, Hawai'i.

The Army is using a three-part process for assessing health and possible cleanup issues on Army ranges in Hawai'i. A historical site assessment looked at all the possible ranges where depleted uranium, or DU, may have been fired.

The next step was to determine that DU actually was present at Schofield and at Pohakuloa Training Area on the Big Island.

Aerial testing at Makua Military Reservation was inconclusive and the Army is weighing options for further tests in areas that also may pose a danger from unexploded ordnance.

Greg Komp, senior health physicist for the Office of the Director of Army Safety, in Washington, D.C., said a determination of the extent of possible contamination and health hazards will be completed by the end of the year.

Margotta said "once we complete our assessment and analysis we will develop a prudent, proactive and transparent response."

The Army has pledged that the state Department of Health will be a partner in surveying for DU and any remediation plans.

But Kyle Kajihiro, program director of the American Friends Service Committee, a Quaker-affiliated social justice and peace organization, said some in the community want independent analysis and oversight.

"We don't have any confidence in their (the Army's) assessment that it's safe or that public health has been protected," Kajihiro said.

In January 2006, the Army confirmed it had found 15 projectile tailfin assemblies that contained depleted uranium at a Schofield Barracks munitions impact range.

The depleted uranium was used in XM-101 aiming rounds that simulated the trajectory of the Davy Crockett, a formerly classified recoilless rifle that could fire a 76-pound nuclear bomb.

The Cold War weapon was intended to be used as a last-ditch effort against masses of Soviet soldiers in the event of war.

Earlier this summer, the Army said it had found more depleted uranium fragments at Schofield, and that the aiming rounds also may have been fired at Makua Valley and Pohakuloa.

Concern by some Big Island residents that dust containing depleted uranium might be kicked up, spread on the wind and possibly inhaled led to the testing.

An aerial survey of the firing range at Makua Military Reservation was conducted last month, but results were inconclusive because heavy vegetation hid the ground.

Depleted uranium was used for Davy Crockett aiming rounds because its density helped mimick the trajectory of the 76-pound warhead.

When an aiming round was fired, a gray cylinder 3 to 6 feet long would fall away, while the 20 millimeter DU aiming round continued to travel farther, the Army said. The presence of the cylinders is being used as a predictor of depleted uranium.

"We see no immediate danger to the public," said Russell Takata, program manager for the state Health Department's Noise, Radiation and Indoor Air Quality Branch.

"We will continue our vigilance to see the appropriate protocols are taken and ensure we are also part of the solution."

According to the World Health Organization, a radiation dose from DU would be about 60 percent of that from purified natural uranium with the same mass.

Due to its high density — about twice that of lead — DU is used for counterweights in aircraft and radiation shields. DU is used in armor-penetrating military ordnance because of its density, and also because DU can ignite on impact if the temperature exceeds 600 degrees Celsius.

A United Nations report on impact sites in Kosovo indicated that environmental contamination by DU was limited to a few dozen yards around the impact sites.

Reach William Cole at wcole@honoluluadvertiser.com.