The simulated shooting started off Thursday afternoon with dulled, but loud, hand smacks against the glass in the hallway, imitating the popping sound that even combat veterans will fail to recognize as gunfire.

The pops lack any discernible rhythm, save for short staccato bursts, but they do set off a chaotic storm of other sounds over the next 15 minutes — a hysterical teacher’s call to 911, pained screams echoing down the school hallways, a slightly off-sync burst of chirps as dozens of first responders’ radios sound the unthinkable words they pray to never hear:

“Shots fired at Theodore Roosevelt Elementary.”

It’s a nightmare these first responders lived 12 times over the course of the three-day training that started Wednesday, involving several area agencies, like local police and fire departments, emergency medical services and USD 383. Different responders rotated through the simulations in order to provide the training for as many people as possible.

But unlike other nightmares, they know this one could become reality one day, so the trainers and volunteers make every effort to make the training as real as possible. Their job, in a sense, was to make the first responders’ jobs as difficult as possible, to put as much stress as they can on the first responders, so that they have a sense of the even greater stress they’d experience in a real shooting.

“The more we act it out, the more stressed out they are, and that’s what we’re trying to do,” Brooke Black, a four-year volunteer veteran, said. “We stress them out and make sure they don’t miss anything.”

Several of the volunteers, ranging from teenagers to adults, donned moulage — make-up and other effects meant to simulate gunshot wounds and other injuries.

“Once we start, the atmosphere completely changes,” said Eaden Marstall, a Manhattan High junior who’s volunteered the past three years. “Even though it’s fake, it’s extremely serious and grave. As soon as the first responders start treating you, they take it very seriously. The tourniquets are put on tight.”

Whenever school shootings do occur, they act as sobering reminders of why the training matters, but they also serve as learning opportunities. RCPD Lt. Tim Schuck and Manhattan Fire Dept. battalion chief Mark Whitehair, two of the trainers in charge of the simulations each year, said they constantly learn and debrief from other shooting incidents throughout the year.

“We understand it’s just a simulation, but part of what we did to prepare our staff for this is we did a debrief with our staff of the Sandy Hook incident, which really brings it to light for a lot of people, why we have to train and react the way we do,” Schuck said. “Quite frankly, I’d say the vast majority of (us first responders) are parents ourselves, so it really hits home for some of us.”

More than anything, the training has taught area responders to be cohesive, Whitehair and Schuck said. From a bloodied disarray of screaming victims in hallways, the first responders bring some measure of organization, arriving in waves to first stop the violence and then tend the wounded. It’s a careful operation that requires cooperation between several people in several agencies, and only training such as Thursday’s builds the cohesiveness needed in these nightmares.

“When we first started the lack of communication compared to now, it’s been amazing,” Whitehair said. “It’s so fluid. I am proud of all the men and women who take time to participate in this training.”

“It takes a lot of different parts coming together, and we do it as accurately and efficiently as we can,” Schuck said. “At the end of the day, all three agencies have the same goal, and that’s the preservation of life.”

Education reporter for the Manhattan Mercury. Follow me on Twitter at @byRafaelGarcia.