The terrorist tactic of detonating one bomb, then a second more powerful explosive is forcing local emergency personnel to rethink the way they would manage such incidents.
The drill for so-called "first responders" has been to race to the bombed site to rescue the injured. But conventional strategies of swarming a scene with police, paramedics and firefighters are now being revised amid heightened awareness of the possibility of secondary threats.
Long a staple of terrorists around the globe, the double-bomb scenario is most likely to face police and fire agencies as the war in Iraq escalates and the nation ratchets up its homeland-security defenses, authorities say.
Recent bombings in Kabul, Afghanistan, and Bali, Indonesia, have underscored a need for new procedures to protect victims and rescuers. In Southern California, the handling of the July 4 shooting at Los Angeles International Airport exposed potential vulnerabilities.
"This is becoming a hot-button issue," said John Miller, commanding officer of the Los Angeles Police Department's Counter-Terrorism Bureau.
Even as those entrusted with public safety search for ways to deal with the probability of secondary attacks, authorities across California acknowledge that training and preparedness is lagging.
"I cannot think of an agency that has a model protocol on this, and that's a bad sign," said Bruce Gadbois, who oversees terrorism training for the state Office of Emergency Services.
Unlike authorities in Israel or Northern Ireland, who have learned from years of experience, local police and fire officials have only recently moved tactics for secondary explosions to the tops of their agendas.
Training varies, depending on the agency, but the state recently provided a $1-million grant to standardize responses by paramedics and firefighters to terrorism incidents, including secondary attacks.
"We recognize these shortcomings.... 9/11 changed a lot of people's views," said Carroll Wills of the Sacramento-based California Professional Firefighters, a statewide labor group that helps to train rescuers under the state grant.
Many patrol officers and front-line paramedics are being taught to assume that a secondary device is at every bombing incident. Instead of rushing in, rescuers are told to slow down and look for cars, satchels, people and even bottles that seem out of place.
"We train our personnel" to be very aware, to "take a look around for anything suspicious," said Capt. Steve Wood of the Glendale Fire Department, who oversees anti-terrorism planning for the city.
Police and fire departments also are trying to better coordinate efforts between emergency medical crews and officers who secure the area and search for bombs. This includes increasing the availability of bomb-sniffing dogs and positioning police and fire vehicles as defensive barriers around triage areas.
California fire and law enforcement officials have traveled to Israel to examine patterns of dual blast attacks favored by such Islamic extremist groups as Hamas. Many attacks have been aimed at government rescuers -- those whom people depend on for protection -- for added psychological effect, officials say.
"Terrorists go out and do practice runs" with false calls to observe emergency response practices, said LAPD Sgt. Christopher Booker, a terrorism training supervisor. "They study how police respond."
As a result, officials across the state are stressing that squads should vary their emergency routes and find alternate locations for command posts and on-scene treatment areas.
"We're telling the guys, 'Don't have patterns,' " said Sgt. Mike Fernandez, supervisor of the San Jose Police Department's bomb squad.
In some cases, rescuers are being trained in "swoop and scoop" tactics. "If somebody's hurt," Fernandez said, "you grab them and get them out of the hot zone."
Some law enforcement officials are hoping to get help in managing secondary explosions from new technologies, such as "blast suppression" foam. Typically, a tent or bag is placed over a suspect car or possible bomb and foam is pumped in to absorb the shock and shrapnel of an explosion.
Nowhere in California is the concern for a secondary attack more acute than at LAX, considered the region's top terrorist target. Authorities say they have adjusted their tactics since the July shooting at the El-Al Airlines counter, which authorities said was not an organized terrorist attack.
After the gunman opened fire, killing two people before being shot to death, thousands were evacuated from airport terminals. Many were herded by authorities onto the upper deck roadway, creating what counter-terrorism experts call a "fatal funnel" that exposed large numbers of people to a possible secondary attack.
Officials now acknowledge that was a major mistake.
"You don't evacuate a large airline terminal and leave 2,000 people on the central terminal roadway," said Mark Leap, assistant commanding officer of the LAPD's Counter-Terrorism Bureau. "That was one of the lessons learned."
Leap said officials have changed some of their tactics and response procedures to protect rescuers and travelers at the airport.
Officials are reluctant to discuss specific strategies, but Leap said that, in the event of future incidents, travelers would be taken to secure areas. He said LAPD and airport police have recently held major training at LAX with fire and paramedic crews, including a drill in January simulating multiple shooters and explosive devices.
Even with the new awareness, veteran police and fire rescuers say they still expect to face wrenching decisions as they roll onto scenes that could involve secondary attacks. Do they rush in to aid victims? Or do they hold back to avoid becoming part of the problem?
"That would be very hard to live with -- that we waited outside while someone died," said Capt. Dan Cypert, a 34-year veteran of the Los Angeles Fire Department. He supervises paramedics at LAX and was among the first responders at the shooting scene last July.
Despite advancements in secondary blast training, Cypert expects that "we're going to have people go in and some of us are going to get killed."
"It's a sad commentary," he said, "but it's one of the hazards of the job."