Inside the SGC

Typical corridor from level 20 on down in the SGC.
The Gateroom
When a wormhole is first established it is unstable. This wave can disintegrate anything it touches. A safety zone is established around the gate, so that no personnel are in the area of the wave until the wormhole is stabilized.
Once a wormhole is stable, objects and personnel can safely enter the event horizon.
The wormhole cannot pass matter both directions. Only from the originating gate to the destination gate. Electronic signals seem to be the exception to this rule.
The iris seals the stargate so that nothing can reintegrate on this side. This protects the SGC from unwelcome guests, But it also kills anyone tryng to come through. Like a bug hitting a windshield. The iris can not be closed while a wormhole is being established or it would be destroyed by the instability pulse.