2 Answers

Cancer Worries for New U.S. Bombs

The U.S. military is working on a small, precise bomb that could hit targets "previously off limits to the warfighter." The problem is, it might cause cancer.

Dense Inert Metal Explosive (DIME) is one of the Air Force Research Laboratory’s responses to the challenge of fighting in an urban environment without hurting innocent bystanders in the process.  couldnt find much on the christmas island bit but this was quite interesting

Recent news about an airstrike which may have killed civilians, as well as Taliban fighters, highlights the problem. Similar situations have occurred repeatedly in Iraq and Afghanistan; sometimes targets could not be engaged, because of the risk of harming nearby civilians. One option is to use smaller weapons. Another is dropping inert bombs, filled with concrete rather than explosives, to minimize collateral damage.

DIME.jpgBut what's really required is something which is just as lethal as a standard bomb, but keeps its lethal zone to a minimum. This is exactly what DIME delivers.

DIME is used in the Low Collateral Damage version of the Small Diameter Bomb currently under development. This has a carbon fiber casing which turns into dust rather than creating dangerous fragments. The bomb is filled with explosive mixed with tungsten powder, which becomes micro-shrapnel. The small size tungsten particles means that the drags them to a halt at about 40 charge diameters. In the case of the SDB, that gives a destructive radius of about 25 feet.

The result is an incredibly destructive blast in a small area, what the Air Force Term "Focused Lethality." The AFRL Munitions Directorate provided this picture of a DIME test, but were unable to discuss the topic. However, I talked to others who have worked in this area. They were consistently awed by the destructive power of the mixture, which causes far more damage than pure explosive within the near field. The impact of the micro-shrapnel seems to cause a similar but more powerful effect than a shockwave.

Early blasts even destroyed test instruments:

Unfortunately, the high-velocity, high temperature inert metal particles found in DIME fills have proved to be extremely damaging to traditional pressure measurement instruments. Hence, new measurement diagnostics had to be developed to investigate DIME formulations.

Because there are no large fragments, Focused Lethality Munitions should not cause a hazard at any great distance. The standard Small Diameter Bomb is claimed to be lethal out to 2,000 feet or more, the Focused Lethality version will have a smaller but deadlier footprint - a 12-gauge compared to a rifle.

DIME2.jpgLittle has been released on the exact effects of DIME explosives, but it’s interesting that a presentation on future munitions illustrates focused lethality with a tank which had been turned on its side by blast. Aimed accurately, it looks like it would be capable of destroying a building completely without damaging the rest of the neighborhood.

Metal powders -- typically aluminum -- have been added to explosives for many years. But those are reactive metals, making the blast even stronger. Tungsten, on the other hand, is inert. So it remains in metallic form and absorbs some of the energy of the explosion. DIME originated in work to increase the density of the explosive mixture, improving the penetrating power of bunker busting bombs. But the bonus effect of the micro-shrapnel proved to be more significant than the increased density.

The Air Force's focused lethality munition had an enthusiastic write-up in the Wall Street Journal. The US Navy's Surface Warfare Center at Dahlgren is also working on DIME munitions.

According to the Air Force’s FY 2007 Unfunded Priority List, the focused lethality munitions "will be able to prosecute targets previously off limits to the warfighter."

This suggests that they will be used in close proximity to civilians or friendly forces. The only collateral damage may be stray tungsten particles – clumping, or larger particles in the mix might mean some effect outside the focused zone. Would grains of inert tungsten present a problem? According to New Scientist magazine:

In a study designed to simulate shrapnel injuries, pellets of weapons-grade tungsten alloy were implanted in 92 rats. Within five months all the animals developed a rare cancer called rhabdomyosarcoma, according to John Kalinich's team at the Armed Forces Radiobiology Research Institute in Maryland.

92 out of 92 - "tumor yield was 100%" - is a significant result. The full report is here.

I checked with University of Arizona cancer researcher Dr. Mark Witten, quoted in the New Scientist story, to see how things have developed. Dr. Witten is investigating links between tungsten and leukemia, and is concerned about its possible use DIME or other munitions:

"My opinion is that there needs to be much more research on the health effects of tungsten before the military increases its usage."

We don’t know whether a Focused Lethality Munition is likely to result in tungsten particles striking anyone outside the lethal area. Nor do we know the possible environmental impact tungsten powder left afterwards. But given that the Focused Lethality munition will be used in situations which are likely to produce media attention and political repercussions, these should be addressed.

The aims of the Low Collateral Damage program are worthwhile. But unless the issues around tungsten are resolved we could see a repeat of the depleted uranium story. Instead of decreasing controversy, the new weapon might create even more.

-- David Hambling
May 22, 2006 09:24 AM