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Along a path at the edge of a weed-ridden farm in Cambodia, a man listens carefully as he sweeps his metal detector over the ground. When the detector’s squealing tone signals the presence of buried metal, the man stops, repeats the sweep, and carefully marks the spot. Soon a second worker follows and lies on the ground, his head an arm’s length from the marked spot, gently probing the ground with a stick. Both men are experienced deminers, one a retired British Army veteran far from home, the other a local resident trained to find mines. Both know well the cost of error: sudden serious injury or death.

After probing the hard dirt with concentrated care for about 20 minutes, the prone worker judges by sight and feel whether he has hit the rounded metallic body of a buried mine or merely the random detritus of an old battlefield: a bullet, a piece of shrapnel, a length of wire, an empty tin can. He knows that in some fields the odds are as low as one in a few hundred that the detected metal is actually a mine, but his partner’s metal detector cannot distinguish an explosive device from any other object that holds a fraction of an ounce of metal.

Whatever it is, the metallic object must be carefully exposed to reveal its form and color. If it is a mine the workers will place a modest explosive charge beside it, unspool long wires, and retreat 100 yards to blow it up. Then the task will repeat itself: the operator of the metal detector will resume his patient sweeping, listening for signs of the next buried metallic object in his path while his partner waits for his next tense trial in the dirt.

According to United Nations estimates, more than 100 million mines lie buried around the world, outlasting their wars, abandoned long ago yet awaiting their unintended victims for as long as decades. An anti-personnel mine costs only a few dollars to produce, but it now costs a hundred times that sum to remove it. In Cambodia alone, where some of the world’s densest minefields lay, roughly 10 million mines lurk within an area the size of Missouri. Last year three thousand workers cleared landmines from 12 square kilometers of Cambodian land at a cost of $8 million. They were not overpaid. But at that rate, even if someone were willing to foot the bill, demining Cambodia would take some 10,000 years. To make matters worse, participants in today’s conflicts are emplacing new mines at a rate 10 or more times the current yield of the deminers, who now clear perhaps 100,000 mines per year worldwide. A chronic and growing crisis is at hand.

Most poignant is the human toll that the residual landmines claim: some 10,000 deaths annually and at least twice that many serious injuries, with victims including many small children and elderly villagers in poor nations. In Cambodia, landmine accidents have resulted in one amputee per 250 people. Yet clearing away lingering landmines is not needed just to protect human life and limb. Over the long term, landmines disrupt normal economic activities such as travel and transport, and deny vital cropland to farmers, often causing hunger and forcing sizable agrarian populations to migrate to urban centers and refugee camps.

Today, the use of a metal detector, hand-held probe, and explosive charge is generally accepted as the most reliable demining method despite its laborious and perilous nature. The detection method works because most mines have metallic casings or at least contain a few grams of metal, usually a firing pin and its associated spring, setting off a signal in the detector even when a mine is buried or hidden beneath overgrown vegetation.

The bottleneck occurs, however, in discriminating between the few real mines and the many false alarms. Given the wide array of metal objects that can reside in the soil of former battlefields, the false-alarm rate can run as high as 1,000 false positives to one real mine. The result is that the bulk of the searcher’s time is spent on the painstaking exposure of harmless metal scraps. And after hundreds of false alarms, the job becomes even more perilous: one surprise mine can maim or kill deminers whose patience has flagged just once, causing them to misjudge the form they uncover. What’s more, growing use of plastic-encased mines poses the ominous threat of false negatives: that real mines will remain silent-and deadly-even when swept by a metal detector.

Despite the admittedly grim situation, though, we find some cause for optimism since reviewing the global landmine problem at a week-long meeting last summer. Conducted by the MIT Program in Science and Technology for International Security at the American Academy of Arts and Sciences in Cambridge, Mass., the meeting drew together a disparate group of participants, including a field worker from Laos with many years of demining experience; researchers with expertise in physics, chemistry, electrical engineering, material science, and anthropology; several people working on high-tech mine-detection schemes; and three experts on demining from the military who brought the group a sobering collection of anti-personnel mines (without explosives). Our unexpectedly hopeful view, bolstered by subsequent study, is that while no silver bullet appears to be on the near horizon to solve the demining problem, promising technologies at hand can offer significant help. A number of developing techniques, for instance, detect landmines by sensing physical and chemical properties other than metal content, thereby significantly aiding in the task of reliably discriminating mines from metal scrap. Our analysis indicates that if nations lend enough support, affordable technologies could be available in the field within five years to undertake a humanitarian demining effort on an unprecedented global scale.

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