Is your city prepared for a home-made nuke? - science-in-society - 08 July 2009 - New Scientist

Is your city prepared for a home-made nuke? - science-in-society - 08 July 2009 - New Scientist

AS US president Barack Obama visits Moscow this week to discuss nuclear arms reduction with his Russian opposite number Dmitry Medvedev, a different nuclear threat is preoccupying emergency planners back home. A panel of medical experts has just released its assessment of the technologies and therapies that could be rolled out if a home-made nuclear bomb was ever detonated in the heart of an American city.

A device of this kind - now judged by Obama to pose "the most immediate and extreme threat to global security" - would kill hundreds of thousands of people. But as catastrophic as such an attack would be, it would not level an entire city, and a timely response could save many lives. Recent advances in techniques for mapping the path of radioactive fallout after an attack, combined with novel therapies for treating radiation victims, will improve survival chances, the report says.

"Clearly there would be loss of life, but it's not hopeless," says Georges Benjamin, head of the panel of doctors and public health officials that was convened by the National Academy of Sciences to assess the nation's level of preparedness for such an attack. "We feel that there are things that one can do to mitigate it."

So what would a city need to do? The panel explored the consequences of a nuclear explosion packing a punch equivalent to 10,000 tonnes of TNT. That's tiny compared with the thermonuclear weapons deployed by the US and Russia - and smaller even than the 15-kiloton bomb dropped on Hiroshima in 1945 - but plausible for an improvised device.

The blast wave would destroy buildings and kill almost everyone within 1 kilometre (see map), so the panel focused its attention on people outside this zone, for whom the main danger would come from radioactive fallout. "That's a place where you could get big gains if you plan right," says panel member Fred Mettler of the New Mexico Veterans Administration Health Center in Albuquerque.

Highly radioactive rubble and dust thrown up by the explosion would rain down on the surroundings, emitting lethal gamma rays. The wind could carry deadly levels of fallout several kilometres in just a few minutes - too fast for anyone to outrun it. People attempting to drive out of danger on clogged roads would fare little better, as cars offer scant protection from gamma rays.

For many people, the safest option would be to seek shelter in buildings or underground. Just staying inside could slash the immediate death toll from radiation by up to a factor of 100, or even 1000, Mettler says. However, people must be told this in advance. "Without prior education, it would be a horrible issue," he says.

Just staying inside could slash the immediate death toll from radiation by a factor of up to 1000

One crucial factor will be for the authorities to get an instant picture of where the fallout is going and its quantity and speed. This will make it possible to figure out who should seek shelter and who should evacuate - and in which direction. It will also ensure that rescuers are not sent on "suicide missions" into areas of high radiation.

The National Atmospheric Release Advisory Center (NARAC) at the Lawrence Livermore National Laboratory in California has for years been charged with providing predictions to emergency planners within a few minutes of serious incidents involving a release of radioactivity. NARAC's model would be used to guide planes and helicopters equipped with radiation detectors, whose measurements would in turn refine the model's predictions.

NARAC is now working to improve its modelling software to take into account variations in wind speed and direction in three dimensions and fluctuations over time; the last version assumed winds vary only with height. It will also take into account the way rain can scrub fallout from the air and deposit it on the ground. While this would prevent fallout drifting so far, it would also mean that larger amounts of radiation are deposited sooner and in different places than if there were no rain.

Even with prompt predictions and the possibility of broadcasting them by radio, it is likely that many people would not be aware of what they need to do or would fail to reach shelter in time. The result would be exposure to high levels of radiation, which inflicts its most immediate damage on rapidly dividing cells such as bone marrow and the lining of the gut.

Damage to bone marrow leads to reduced production of key immune cells and blood-clotting platelets. Very low levels of platelets can trigger dangerous bleeding even without any injury. Damage to the gut lining triggers internal bleeding, which is worsened by a lack of platelets. This in turn allows bacteria to leak into other parts of the body, resulting in potentially deadly infections, which are made worse by the lack of immune cells.

Two drugs approved last year could help cut down such complications, says panel member Nelson Chao of Duke University in Durham, North Carolina. Amgen's Nplate (romiplostim), and GlaxoSmithKline's Promacta (eltrombopag) were approved for use in people with a rare condition that keeps their platelets in chronically short supply. Chao says they might also help boost platelet numbers in radiation victims, preventing dangerous blood loss and infections.

It may also soon be possible to use what are known as progenitor cells to prop up the patient's immune system while the bone marrow recovers. Developed by Cellerant Therapeutics in San Carlos, California, to help cancer patients undergoing radiotherapy, progenitor cells are part-way along the developmental path that starts with bone marrow stem cells and ends with immune cells like white blood cells.

The therapy is still experimental. Results being presented at a stem cell meeting in Barcelona, Spain, this week show that mice start producing immune cells within a few days of being injected with progenitor cells. Elsewhere, a trial in 25 patients undergoing radiotherapy began in May.

The cells can be grown in the lab and frozen until needed. If they are found to be safe and effective, they could be stockpiled for use in case of a nuclear attack, says Ram Mandalam, CEO of Cellerant.

Even if progenitor cells do prove effective, Chao points out that meeting the sudden surge in demand following a nuclear attack would overwhelm a city hospital. Mandalam suggests the solution would be to transport patients to treatment centres farther away. According to Mettler, this and other medical therapies might cut the radiation death toll by a factor of 3.

The federal government has yet to respond to the report, though Benjamin points out it is still early days. "This is hot off the press," he says. "We've literally just briefed them."