Peeling back the onion
Digital radios often are not compatible with fireground settings or equipment used by firefighters, according to a national laboratory test and recommendations released last month by the International Association of Fire Chiefs (IAFC) Digital Project Working Group.
While the focus is on the failure of digital radios to provide the communications needed in certain fireground scenarios, IAFC senior adviser Alan Caldwell noted that analog radios often have the same problems in such settings.
“There’s a lot more to this than, ‘Digital’s bad and analog’s good. If you get an analog radio, you’ll be fine. If you get a digital radio, you’ll die.’ That’s not the case at all,” Caldwell said. “When you operate in the kind of environment a fire service operates in, there’s going to be loud background noises. If you get it loud enough, nothing’s going to get through, no matter how good [the technology] is.”
Indeed, the National Telecommunications and Information Administration (NTIA) stated in its report that all three communications systems — 25 KHz analog, P25 full rate and P25 enhanced full rate (12.5 KHz analog was tested on a limited basis) — failed to deliver intelligible communications in four of the nine fireground environments tested.
All systems tested met National Fire Protection Association standards of 80% intelligibility when no self-contained breathing apparatus (SCBA) masks or background noise was involved. However, when a firefighter uses an SCBA mask or personal alerting safety system (PASS), digital systems often were not as intelligible as analog systems, according to the NTIA report.
The IAFC last year formed a working group to study the problems firefighters were experiencing when using digital radios in the presence of loud background noise — not only from power tools such as chainsaws often found at a fireground, but also from alert mechanisms included in a firefighters’ apparatus.
“We have to look at the protective envelope around a firefighter as a system,” said Charles Werner, IAFC working group chairman. “You have to look at how the different components work with the radios.”
While 12.5 KHz analog systems were tested in three environments — performing similarly to 25 KHz analog systems in those instances — they were not tested in all nine environments like the other systems. With the FCC mandating 12.5 KHz channels below 512 KHz in a few years, such systems “should be evaluated further,” according to the NTIA report.
Indeed, the issue of narrowbanding is likely to create even greater vocoder challenges, as the FCC already has indicated its intention to have public-safety communications systems eventually operate on 6.25 KHz channels.
“The real issue here is the compression issue — the issue that we have to operate with less spectrum,” Caldwell said. “Therefore, you’re trying to compress all this into a smaller swath of electromagnetic particles, and it just makes it more difficult.”
The IAFC was expected to release its interim report on digital radios shortly after MRT‘s press deadline. The report will provide a summary of the findings to date and some recommendations to alleviate the problems, Caldwell said. Among other things, the IAFC suggests the need for audibility standards and for manufacturers of firefighting equipment to consider radio communications when designing products.
Although the IAFC interim report may be the most comprehensive document regarding the use of digital radios on the fireground, Caldwell acknowledged it is only starting “to scratch the surface.” Meanwhile, fire departments currently using digital radios are advised to consult the IAFC’s best-practices presentation.
From a technical perspective, the best practices recommend that firefighters use speaker, in-throat and in-ear microphones when practical to reduce the impact of background noise on digital-radio communications. The IAFC working group also recommends that system managers consider background noise when making their personnel deployments, work with manufacturers to optimize settings for existing equipment and get involved in development of new communications systems.
