Investigators say the fire on Glasgow’s Union Street develops and spreads through concealed void spaces within the building before firefighters arrive. According to updates from local fire officials reported by two outlets, preliminary probes indicate the blaze took hold within the building’s voids and then spread quickly through them. The reports describe the spread as “rapid” and suggest that the presence of these hidden spaces played a significant role in how the fire intensified. Both sources frame the accounts as early-stage findings from initial investigation work, conducted after emergency services respond to the incident. They do not provide additional confirmed details in the excerpts about the exact origin point, whether an ignition source has been identified, or the full extent of damage. The information is presented as part of an ongoing investigation, with further inquiries expected to clarify how the fire started and how it moved through the structure.