• —Large building size — schools, malls, hospitals, campuses, hotels, warehouses, and stadiums absorb and isolate sound
• —Modern building construction — concrete, steel, fire doors, soundproofing, and sealed classrooms dampen gunfire noise
• —Distance from the threat — officers entering from the exterior may be hundreds of feet from the suspect
• —Intermittent shooting — active shooters rarely fire continuously; pauses between shootings, movement between rooms, reloads
• —Competing environmental noise — fire alarms, PA systems, screaming crowds, HVAC, echoes, sirens outside
• —Directionality and echo distortion — gunfire inside structures echoes unpredictably; officers may misidentify direction
• —Suppressed weapons — some suspects may use suppressors or smaller caliber weapons that sound less obvious indoors
• —Stress-induced auditory exclusion — under high stress, officers may experience diminished hearing or tunnel perception
• —Multiple barriers — closed classroom doors, stairwells, elevators, firewalls, utility corridors
• —Victims hiding silently — once people shelter in place, screaming and movement may stop even though the threat remains active

Silence does not mean safety. The absence of gunfire is only one piece of stimulus information.

Officers must interpret the totality of stimulus:

• —Fleeing victims
• —Fresh intelligence from dispatch or witnesses
• —911 updates
• —Smell of gunpowder
• —Visual indicators
• —Time-sensitive casualty information