The answers to this question explain that "lock the doors" is part of the standard NASA procedure when an accident occurs. Securing the mission control center helps preserve evidence that will be needed for an investigation and gives personnel uninterrupted time to document what they know.
That question was about Columbia, and the answers therefore only discuss mission control in Houston. However, the Challenger disaster occurred soon after launch from Kennedy Space Center. Does KSC have the same or similar procedures after an incident?