DENTON -- Emergency responders from across the region gathered in Denton for a massive training exercise. Throughout the simulation, hundreds of patients pushed the resources to the limit.

Samantha Pickett, a University of North Texas graduate showed WFAA the trail of damage the simulated explosion left behind.

"We have the debris here mixed with the patients," Pickett said.

Video shot inside the simulation shows just how real a training exercise can get.

Here's the scenario: an attack has taken place on the UNT Campus, the fake attack is modeled after the Boston Marathon Bombing. In this case an improvised explosive device goes off inside Apogee Stadium on game day.

"We hope and pray this never happens but we want to be as ready as we can just in case and I feel like exercises like this help us to be better prepared," said Michael Penaluna the Emergency Management Coordinator for the City of Denton.

Crews stationed near the school arrived on scene at the drill immediately while UNT took the opportunity to set up new drone technology.

WITH? what is situational assessment "The eye in the sky we can see situational assessment -- we can see where the victims are," Penaluna said.

Two cameras on board the drone send back a side-by-side picture: the one on the right is a special thermal camera that shows body heat.

Friday's training took one year of planning and called on the recourses of dozens of departments and almost 500 personnel to pull off.

"Seeing all these shootings and things like that, I mean it's heartbreaking to see and a real eye opener that we need to prepare ourselves," Pickett said.

It comes the same week Irving police locked down Northlake College to search for a gunmen that killed a 20-year-old student before killing himself.

"I worry about my friends all the time, I have friends at North Lake College in Irving and that live near there too and it's a big eye-opener just prepare, prepare, prepare," Pickett said.

The drill only lasted a few hours, but the real work comes after. Crews will examine their response and will look for ways to better respond to an event they hope never actually comes.