What's a Fair Warning When It Comes to Bombs?

LONDON (Feb. 23) -- Northern Ireland's police chief has condemned dissident members of the Irish Republican Army for giving his men less than 20 minutes to clear the center of a town before detonating an explosives-packed car.

"The time we got to respond was very limited," Northern Ireland's chief constable, Matt Baggott, told reporters. "It was reckless and callous."

The 225-pound car bomb that terrorists rammed into the gates of Court House in Newry, 30 miles southwest of Belfast, on Monday night went off just 17 minutes after police received their first telephone warning. The explosion -- the first of its kind in Northern Ireland in nearly a decade -- happened as locals were being evacuated, and police say it was a miracle that no one was killed or injured.

So what would constitute a fair warning? And how long do security forces need to safely move citizens away from a ticking time bomb?

Colin King, the founder of mine clearance firm C King Associates, says authorities require far more than 17 minutes. "The general rule of thumb for a bomb of that size is that you'd need to evacuate people within a 200-meter radius," he told AOL News. "If you draw a 200-meter radius circle on a map of a town, you'll realize the sheer number of properties involved. And imagine if you only had a dozen policemen available -- how many houses could they really get to in under 20 minutes?"

People outside that immediate danger zone may also be at risk. Narrow streets channel blasts, sending secondary fragmentation such as broken glass and roof tiles shooting far beyond the 200-meter area.

King, who served as a bomb disposal officer in the British army for 14 years, added that planning a "safe evacuation route would also take quite awhile. You have to think about whether people will be led past points where they're going to be vulnerable."

Depending on the street layout and the location of the blast, for example, the glass of some buildings may be blown in, while in other places it'll be sucked out, endangering anyone walking by.

The fact that there were no injuries Monday night could be attributed to the fact that the police in Northern Ireland became evacuation experts during the dark days of the 30-year-long Troubles, when the IRA regularly planted vehicle bombs of up to 2,000 pounds. However, when these explosives were placed in civilian sites, the IRA (which disarmed in 2005) often gave a telephone warning more than 30 minutes before detonation. Its primary goal was to inflict costly financial losses through the destruction of property.

The IRA splinter groups now attempting to blast apart the province's successful peace process take a much more cavalier attitude toward public casualties. In August 1998, the Real IRA dissident faction warned police that it had left a car bomb outside the courthouse in Omagh. Officers duly moved shoppers and locals away from the building, but unwittingly led them into the face of the real explosion. Twenty-nine people -- Catholics and Protestants, men, women and children -- were killed, the heaviest toll of the entire conflict.

The terrorists who planted Monday's bomb were similarly unconcerned about killing innocents. "I suspect that their calculation of how much warning to give police was driven more by the possible reaction time of bomb disposal officers than the fate of the ordinary people," King said. "They might have thought that if they gave more than 30 minutes warning, there'd be a chance that a bomb disposal team could get on site, identify the target and then make it safe."

But, he adds, when it comes to bombs in public spaces, there's no such thing as a fair warning. "Police and bomb disposal teams are never going to get enough time," King said. "You simply can't put a figure on it."