Audibility and Intelligibility
The growing importance of communications in emergency notification.
NFPA Journal®, March/April 2008
We know that clear communications are important in everyday life. Every life-threatening event in a high-rise or large assembly building drives home their importance.
Over the last few code-revision cycles, the Notification Appliance Technical Committee has worked hard to introduce the concept of audibility and intelligibility as they apply to fire alarm systems into NFPA 72®, National Fire Alarm Code®.
The committee also introduced recommendations for mass notification systems (MNS) in the Annex of the 2007 edition of NFPA 72, and the Correlating Committee has proposed a new chapter with specific requirements for all emergency communications systems, including MNS, for the 2010 edition.This is especially important as only mass notification systems may take priority over fire alarm systems during a priority MNS event.
The problem we seem to encounter as we move forward is that many in the fire alarm and enforcement community cannot seem to move away from traditional concepts of emergency voice/alarm communications. Perhaps they do not appreciate that the goal in measuring the effectiveness of such systems is that those receiving the messages understand them. They may also fear that combining a communications system with a fire alarm system will not allow them to meet code requirements.
For years, fire alarm designers and installers specified the placement of one or two speakers in an area and assumed that, as long as an occupant could hear sound by standing near one of them, the system passed muster. They have now discovered that when an authority having jurisdiction (AHJ) enforces the audibility and intelligibility requirements of the current code, their former designs and installations prove inadequate. To meet the code requirements, they may need as many speakers and amplifiers as one might find in a music and paging system in the same building space.
Most building codes and NFPA 101®, Life Safety Code®, require some form of communications system in assembly occupancies. For example, the 2006 edition of NFPA 101 requires "assembly occupancies with occupant loads of more than 300..." to have a voice communication or public address system, except where, "in the judgment of the authority having jurisdiction, adequate alternative provisions exist...for the discovery of a fire and for alerting the occupants promptly."
The NFPA 101 Technical Committee allows the required fire alarm system to "activate an audible alarm in a constantly attended receiving station within the building when occupied for purposes of initiating emergency action." And occupant notification must "be by means of voice announcements, either live or prerecorded, initiated by the person in the constantly attended location."
NFPA 101 addresses audibility in general, but it does not require the level of intelligibility defined in the 2007 edition of NFPA 72. Further, NFPA 101 only requires an emergency voice/fire alarm system when the AHJ determines that a constantly attended location is impractical.
I understand that most owners want to reduce costs by eliminating duplicate systems. From a fire protection management standpoint, a public address system need not meet any specific code or standard, except NFPA 70®, National Electrical Code®. Without requirements, the design of such a public address system may not be robust enough to meet acceptable levels of audibility and intelligibility for the occupants’ emergency communication needs.
Some might argue that a public address system does not fulfill its purpose if it cannot deliver audible or intelligible sound. However, one must judge whether the system can deliver audible, intelligible communications in a building overcome by the chaos of an emergency.
The proposed changes to the 2010 edition of NFPA 72 will help meet this need. The newly appointed Chapter 12 Technical Committee has proposed requirements for existing public address systems used as emergency systems and for allowing the use of fire voice/alarm communication systems as paging systems. The technical committee’s goal is to ensure a minimum level of performance and reliability for all communications systems.
The current requirements for intelligibility and audibility go a long way to ensuring that a fire voice/alarm communication system is as clear or clearer than a paging system. But no owner should have to bear the cost of both systems when they perform equally well. And through the new requirements in NFPA 72, the fire protection community should willingly offer alternatives. Using a fire alarm/voice communication system for daily communication helps ensure that it operates reliably in an emergency.
By taking the lead through appropriate new requirements, the NFPA 72 Technical Committees is certain to meet the communication needs of the future.
Wayne D. Moore, P.E., FSFPE is a principal with Hughes Associates and immediate past chair of the NFPA 72 Technical Correlating Committee.