How is the Berg described in Chapter 3? What happens when the Berg's ramp opens up?

Alec has heard that supply Bergs have PFC painted on them, for Post-Flares Coalition. But the current Berg has no markings of any kind. A crowd gathers, and the Berg opens up. Five people leave the Berg in body suits and helmets with visors. They carry black tubes which look like guns. They fire darts at the people around them, hitting many, including Darnell. Mark and the others run.