The London bombings last summer highlighted the vulnerability of mass transit to terror attacks, and scientists are pushing to develop new gadgets to detect explosives and other hazards. But as some of these technologies come up short or prove tricky to implement, some law-enforcement agents have begun to speak wistfully about the olfactory prowess of man's best friend. As sensitive as the canine nose may be, however, dogs are not well-suited to the challenges of mass transit. It's just not where they do their best work.
Dogs are acclaimed for detecting minuscule amounts of myriad compounds. Their noses are 100 times to 10,000 times more sensitive than human noses, depending on the scent. And they can identify particular odors within a complex mixture "which should be useful for detecting explosives, since many are a potpourri of scents. (There are around 19,000 known smells associated with explosives, grouped into chemical categories of nitrate compounds and acid salts, as well as chlorates, peroxides, acids, and others.) Dogs can also home in on target scents, even when other strong smells are present. Well-trained canines have proved valuable in searching for narcotics and explosives in airport luggage, sniffing out land mines in places like Afghanistan, and ensuring that there are not bombs behind the wall panels in rooms where high-level meetings are to take place. A California clinic now claims it has trained three Labradors and two Portuguese water dogs to detect lung cancer in the breath of patients. Dogs' accuracy is the stuff of legend, which is why, in urban police departments, dogs are considered strong deterrents to would-be criminals.
There's nothing wrong with using dogs to walk the subways to deter crime and make people feel better. But their noses can't be relied on there. I wouldn't want to be the one who put it out to the public that the emperor has no clothes, the head of a large urban bomb squad told me. But dogs do not function in the way everyone thinks. It is, quite simply, bullshit, he says, to think that dogs can walk through subway cars, or sniff people entering turnstiles, and detect whether they've brought explosives along for the ride.
For one thing, dogs work best in quiet places that have been cleared of people other than their handlers. In airports, they are best at sniffing luggage in secluded baggage areas. Canine performance has also been shown to fall off exponentially, the bomb expert said, because of distractions like gusts of air, noise, food, and people "all realities, of course, of mass transit. Bomb-sniffing is also exhausting work "a kind of sensory sprint "that dogs can't sustain for more than 20 or 30 minutes out of every couple of hours. And as they move through an area, dogs need constant reassurance and reward; if they aren't talked to, given an explosive to find now and then, and allowed to run back and forth, they may lose interest in the game. The explosives and the scampering would be hard to offer in the subway.
One danger is that tired, cranky dogs will sound false alarms in crowded places. Canines are often trained to signal that they've found explosives by sitting down. But a dog that's been pushed too hard and needs a break is apt to sit as well. It doesn't take too much imagination to see how a sitting dog at rush hour could cause a panic that would result in injuries.
In addition, dogs probably can't be trained to detect the kind of explosives many experts increasingly worry about. Peroxide-based substances like TATP "used by shoe bomber Richard Reid and some recent terrorists in Israel "are unusually unstable "prone to blow up or otherwise react in air. That makes it difficult, if not impossible, to train dogs to recognize their scent, because to do so requires repeated reinforcement and practice, and that would be dangerous for the canines and their handlers.
If dogs are so fallible in loud, crowded places, why was the new TSA program conceived at all? The problem is that the alternatives are so lacking.
The best explosives-detection devicestypically require police officers to rub a swatch of material (often nylon) over peoples' hands or bags and then chemically analyze the result. If a person has been tinkering with a bomb, trace quantities are likely to show up on him or the things he's touched. Recently, at an NYPD outfit near Coney Island, I watched as a swab dusted with explosive was inserted into one of these machines through an ATM-like slot. Less than 30 seconds later the screen flashed red, identifying TNT.
Devices like this one are being used experimentally in the New York City subway, and on the Boston T at times of high alert. Still, cities have not rushed to embrace them for mass transit because they're prone to error, especially in places like the subway. Some gadgets don't work well in cold weather. Others are susceptible to dust and other forms of contamination. Many flash warnings when testing a person who has taken nitroglycerin (a medication for chest pain) or certain kinds of fertilizers and synthetic fragrances. Some smaller hand-held devices (they look like DustBusters) were supposed to be able to simultaneously detect high explosives like TNT and peroxide-based ones. They probably don't.
Someday, these kinks will be worked out. (Parallel efforts to develop sensors for biological, radiological, and chemical weapons are also under way.) In the meantime, cities are training more cops to pick up on a terrorist's anomalous behavior. As videotapes of thwarted suicide bombings from around the world have shown, a security guard or police officer who confronts a suspicious person can sometimes catch him off guard and stop the intended attack. The best tool for keeping the subways bomb-free still walks on two legs.
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