The Department of Homeland Security’s (DHS) guidance for people in mass shooting situations is outdated and could be costing lives, an expert on mass shootings told ABC News after the Parkland, Fla., high school shooting that killed 17 people earlier this month.

DHS’s advice to “run, hide, fight,” which has been the recommendation since the 2012 Sandy Hook Elementary school shooting in Newtown, Conn., incorrectly advises students to “hide,” which leaves them vulnerable to mass shooters, active shooter prevention expert Chris Grollnek told the news network.

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Grollnek says he estimates that more than 90 percent of fatalities he examined in 13 different shootings were the result of victims trying to hide from their attacker.

“If someone told you there was a bomb in your building, would you get under your desk or would you leave the building?” Grollnek asked. “You would get out. An active shooter is the same thing as a ticking bomb in your building.”

Former FBI special agent Greg Shaffer concurred with Grollnek’s analysis in an interview with ABC, telling students to attempt to flee the area instead of hiding under desks.

“Hiding under your desk is hands-down the wrong thing to do,” Shaffer said. “There needs to be a new shift to stress the importance of getting out of the school building.”

“Those hiding under desks are just making themselves easy targets,” he added.

Shaffer also called on schools to install safety features that can prevent casualties in the event of a mass shooting, such as classroom doors that can be locked from the inside without keys as well as keeping objects such as hammers or screwdrivers that could wound an intruder.

But the experts say running is still a better option.

“The hit rate on a moving target is less than 4 percent so by running, you have a 96 percent chance of getting away and even if you are hit, the fatality rate is less than 0.1 percent,” Shaffer said. “Running is always your best option.”