Common fireground noise, such as some alerting systems and active power tools, can render voice communications from digital radios unintelligible, the International Association of Fire Chiefs (IAFC) said this week in an alert issued to its members.

The IAFC has received reports that voice communications from firefighters using digital radios cannot be heard when the radios are operated in close proximity to the low-pressure alarm of their self-contained breathing apparatus (SCBA), according to Charles Werner, IAFC member and fire chief of Charlottesville, Va.

Upon learning of the issue, Werner had members of his department conduct tests, one of which tested whether a digital-radio voice call could be understood if a chainsaw was being operated three feet away.
“What we found is that, when that loud noise was going off, the voice became totally unintelligible,” Werner said. “When we did the test, you couldn’t tell that the person even said a word.

“In analog mode, you can hear the chainsaw loud in the background, but you can distinguish clearly the person talking. So, we narrowed it down to the fact that it’s a digital problem.”

Specifically, the problem appears to be a problem with the vocoder’s used in public-safety digital radios, regardless of the manufacturer of the device or the frequency band used, Werner said.

“Some of the technical people are saying that the vocoders doing exactly what it supposed to be doing—taking all the noise away and letting the voice be intelligible,” he said. “But the noise is so loud that it’s overwhelming the voice, which is being lost.

“What surprised me was that these digital radios that have been sold to fire departments across the country were never tested in these environments.”

With this in mind, Werner said he will become a member of a working group established by IAFC that will work with vendors in an effort to address these problems. Meanwhile, the IAFC has asked its members to submit any findings they have experienced in such circumstances during tests or in the field.

“The important thing is that we’re hoping we prevent everyone from thinking that digital radio is bad,” he said. “We’ve gained a great deal of benefits and features from the digital side—improvements in coverage, capacity, interoperability and emergency-alerting features—we just have to figure out how we work our way through this to fix this anomaly.”