At high-risk locations around the world, security areas have become an accepted fact of life. The goal of enlarging security areas, obviously, is to protect more people within larger "safe zones." If terrorists can bomb the departure halls at an airport, the logic says, then include the departure halls in the screened perimeter. Fine. But increasing security perimeters introduces problems that actually exacerbate, not alleviate risk.
A central component of airport security around the world is a guarded perimeter around a "sterilized" secure area. Common practice now is to include only the departure concourses (gate areas) in the security area. The question becomes, if departure halls (ticketing areas) were also to be included in airport security, where would security checkpoints have to be located? The answer is; at the entrance to the airport terminal. This does not improve security for the passengers, it simply moves the point at which they can be targeted to a place much more advantageous to terrorists.
In the Brussels attack, the terrorists were forced to use improvised explosive devices, or IED's, small enough to fit into checked luggage, in order to enter the terminal without raising suspicion. This limitation reduced the size of the IED that could be used. Further limiting their ability to do damage was the fact that in a departure hall, absent lines at a counter, the passengers are more uniformly dispersed throughout the area.
If, however, departure halls were moved within sterile areas, the security checkpoints would have to be adjacent to the entrance to the terminals, likely within makeshift structures for climate control. This would mean the screening portal would now be adjacent to the street -- and therefore vulnerable to a car bomb secreted inside a private car, stolen taxi or any other vehicle. A car bomb can easily carry 10 times the explosives of a luggage bomb. Exacerbating this fact, passengers would inevitably be queued up at security lines, grouped tightly together, removing shoes and belts, preoccupied, and with only a thin wall between them and the vehicle-borne device. Think Oklahoma City. Such an attack would kill hundreds, not dozens.
Ironically, the screening lines themselves have created an area of extreme vulnerability. No matter how far out you move the perimeter, a security checkpoint is required, and large groups of people are inevitable.
There is another significant problem with increasing security perimeter size: Resources. As perimeters increase, the area within the perimeters increases exponentially. Soon, there might not be enough resources to adequately secure the sterile areas, rendering them moot. This is not to imply that physical security screenings are useless. Had there not been effective screening in Brussels, the bombs would likely have been on airliners, not in the departure hall. But security must be improved.
Around the world, countries are going to have to make great strides in "human factors" detection as a means to identify potential terrorists. The Israelis have accomplished this with success for years, as have the British. TSA is also employing its version, "screening passengers by observation technique," or SPOT.
All these techniques involve comparing observed behaviors in airports to known behaviors and appearances of terrorists. For instance, in Brussels, the sighting of two men wearing gloves, walking together, with similar luggage, in proximity to a third, possibly disguised man, might have rung alarms.
While critics of these systems allege the techniques are not effective or are potentially discriminatory, that should not dissuade us from employing them. Early screening proved less than adequate, but nobody advocates eliminating it. Should nationality be part of this human-factors screening system? If it isn't, we are intentionally subjecting travelers to significantly increased risk simply to avoid offending some.
So how do we protect the traveling public from terrorism? Perhaps fittingly, the analogy may come from the fight against cancer. Medical science battles cancer in many ways. The goal is prevention, but if that is unsuccessful, early detection is crucial. After diagnosis, chemotherapy and surgery are potential strategies. Ultimately, it is a multidisciplinary approach.
Similarly, terrorism can only be defeated by elimination of conditions that are conducive to the illness. Early detection by law enforcement is essential for success, and once diagnosed, a variety of "treatments" are available. However, unlike cancer, screening to prevent terrorism is the last line of defense, not the first.