Dispatchers rely heavily on people telling them what is going on with victims or patients.
Is someone breathing? Where are they bleeding? This information is key when it comes to helping others before paramedics or fire crews arrive.
But what happens when the other end of the phone goes dead?
Kevin Pagenkop remembers when, as a dispatcher in the Bay Area, he heard the worst sound in the world.
Or rather, as Pagenkop said, there was no sound.
A few years ago, prior to when Pagenkop transferred to San Joaquin County to work for as a supervisor for American Medical Response, he had been a dispatcher for areas that included cities in the Bay Area such as Oakland and Berkeley.
Victims of a shooting in Oakland needed paramedics immediately, so Pagenkop dispatched his team to the scene.
What Pagenkop did not know is that the shooting was still occurring as his paramedics headed out.
As they arrived at the scene of the crime, Pagenkop heard one of the paramedics exclaim that bullets were still flying.
They were caught in the cross-fire.
Pagenkop tried to get them to tell him what was going on, and if they were safe.
But no one responded. The other end of the phone was silent.
"It was the worst sound in the world," Pagenkop said.
Fortunately, the paramedics were able to find shelter and stay safe.
But for Pagenkop, it was a reminder of how frightening not being able to see what is going on can inhibit dispatchers.
"That is probably the hardest part of the job," he said. "You can only hear what is going on. And when there was no one telling me what happened ... it was bad."
Contact reporter Katie Nelson at firstname.lastname@example.org.