Determining intelligibility of emergency messages—not so simple anymore

BURLINGTON, Mass.—The traditional way of deciding whether an emergency message is intelligible is pretty simple, according to a fire protection engineer at a recent emergency management seminar here.

“We all stand around with the fire marshal or AHJ or whoever it is and we play back the message and say, 'Hey, did you understand it?'” said Jack Poole of Olathe, Kan.-based Poole Fire Protection. He gave a presentation on intelligibility at the May 3 event sponsored by Notifier by Honeywell.

But now, he said, new technology to test for intelligibility—intelligibility meters—and new standards have made designing for intelligibility more complex.

In the 2010 edition of the NFPA 72 National Fire Alarm and Signaling Code, “we made some changes, and one of the significant definitions that was added to the code is the acoustically distinguishable space,” said Poole, a member of the NFPA 72 Technical Committee. “The intent is to try to go through your facility and identify spaces that have different geometrical shapes, uses, occupancies, environmental issues and acoustical features. We call those different types of spaces ADSes.”

Poole cautioned that there is a difference between audibility and intelligibility. He said, “Audibility is loudness, and intelligibility is, 'Can I understand what's being said?'”

To evaluate different ADSes in a building, it must be determined which ones have to be audible and which ones need to be intelligible.

For example, an audible emergency message may be needed in a janitor's closet, but one that's intelligible probably isn't. But if that closet also doubles as a break room or a lunchroom, then a warning message that's sent there probably needs to be intelligible.

Poole said a risk analysis of the potential threats to a building also should be done to help determine spaces where intelligibility is needed. He said that in designing a system, everyone needs to agree “what areas need to be intelligible versus non-intelligible to avoid over-design.”