In an emergency, every second counts—and every word matters. Whether it’s a fire, chemical spill, or other life-threatening event, people rely on voice communication systems to guide them to safety. But if emergency messages are muffled, distorted, or unintelligible, the result can be confusion, delayed evacuation, or worse. That’s why speech intelligibility—the measure of how clearly speech is understood in a space—is a crucial, yet often overlooked, aspect of modern life safety systems.
Speech intelligibility is about more than just being able to hear a message; it’s about being able to understand it. Factors like background noise, echo, speaker placement, and system design all affect how well a message comes across in real-world environments. In places like hospitals, schools, airports, and arenas, poor intelligibility can quickly turn a manageable emergency into a dangerous situation.
The 2025 edition of NFPA 72, the National Fire Alarm and Signaling Code, emphasizes the importance of speech intelligibility. According to Annex D of the code, 90% of measurement locations must meet a minimum Speech Transmission Index (STI) of 0.45, with an average of 0.50 or higher. These standards ensure that voice evacuation systems communicate effectively in high-stakes moments.
Testing for intelligibility isn’t just a matter of compliance—it’s about safeguarding lives. Regular testing ensures systems perform as intended, even as buildings change or components age. It also provides documentation that can reduce liability and support audits, inspections, and occupancy approvals.
Speech intelligibility testing isn’t just another box to check during commissioning or maintenance—it’s an essential component of life safety. By routinely verifying that voice systems deliver clear, understandable messages, building managers, installers, and inspectors can help prevent panic, reduce confusion, and ensure faster, safer evacuations.
With NFPA codes reinforcing its necessity and Bedrock tools simplifying the process, speech intelligibility testing should be a standard part of every emergency communication strategy—because when lives are on the line, clarity is everything.