What to Do in Case of a Shooting Like the Newtown School Massacre

Security expert provides tips on getting through an 'active shooter' attack.

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Parents leave a staging area after being reunited with their children following a shooting at Sandy Hook Elementary School in Newtown, Conn.

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Another American town has fallen victim to a gunman bringing wanton violence upon a usually quiet community.

News broke out of Connecticut Friday that a gunman entered an elementary school in Newtown and opened fire, killing at least 27 people, including 18 children.

The media response immediately evoked similar tragedies in recent years, including the shooting at a movie theater in Aurora, Colo., and the Columbine High School massacre.

[PHOTOS: Children, Teachers Flee Mass Murder Scene]

Each incident leaves law enforcement and local officials wondering if they could have done more.

"The unfortunate thing is, we live in a world where as good people we live through our eyes," says Mark Warren, a SWAT veteran and director of training at the security firm Strategos International, which specializes in preparing citizens for so-called "active shooter" scenarios like the one in Newtown.

Americans on average are unable to fathom how a gunman can enter an elementary school and shoot dozens of people, he says, nor does society continue to anticipate for that kind of threat.

"The typical response is, you go for a day saying 'That's tragic,' " he says. "But these people are going to be living this tragedy for the rest of their lives."

[READ: Wrong Person ID-ed as Conn. Shooter?]

"It's unfortunate our society today has to plan for these things, but if we don't, we're being lackadaisical about our children's safety," says Warren.

He offers these tips in accordance with his standard training on how to keep yourself and those around you safe during a mass shooting.

Understand the situation

Teachers, students and staff inside the Newtown school reported hearing booms and noises that resembled hammering at a construction site. In this situation, immediately ask yourself whether any of these could possibly happen.

[READ: Are Mass Shootings A Fact of Life in America?]

"Say, 'We don't have balloons popping in our school hallways. We don't have fireworks going off in our school hallways,' " Warren says. "It starts with that level of awareness."

After assessing the chance of a threat, begin this three step approach:

Lock out

"Be aware of your surroundings and ask yourself, "Can I lock this space out?" says Warren. If you don't have the ability to lock out the space, or if there are too many points of entrance or exit, then:

Get out

Look for other points of exit, such as a window, or ways to get out of the line of sight of a potential threat, such as hiding behind a corner. Once you have moved farther away from the threat, reassess if you are able to walk out.

[RELATED: Live Coverage of Conn. School Shooting]

Always look for ways to escape, and don't rely on locked doors. A shooter in a situation like the one in Newtown—where reports indicate the shooter's mother was a teacher—may have keys or other tools that can force doors open.

Take out

While Warren admits this could be controversial, it may be necessary to fight back with anything you have at your disposal. Warren teaches "velocity of mass" which involves appraising objects for their ability to gain speed, hit hard and do damage if thrown. A fire extinguisher can be one of the best tools for defense, Warren says. Prepare yourself, and show others how they can too.

If you are unable to move out of a room, barricade the door. Remember that the shooter is "on a stopwatch" as soon as the attack begins, Warren says, trying to get the crime done before law enforcement arrives.

"The longer you can prolong this person's means to get access to you, the better chance of getting through this you have," he says.

An ability to survive this kind of attack also depends greatly on planning ahead. So in training teachers and school officials, Strategos tells its students to always begin with the classroom door closed and locked.

In the case of the Newtown shooting, parents' first reactions may have been to rush to the school to ensure their child is safe. Flooding the streets with traffic will only make it more difficult for first responders to get to the scene. A school system should set up a series of locations where parents could wait for more information.