Two ways ERCES coverage is measured
Code-compliant public safety radio coverage is judged two ways, and your AHJ may require one or both:
- Signal strength (dBm) — an objective radio measurement of received power. The most-cited threshold is a minimum of −95 dBm for both the inbound (donor-to-portable) and outbound (portable-to-donor) paths.
- Delivered Audio Quality (DAQ) — a subjective 1-to-5 intelligibility scale. Public safety commonly requires DAQ 3.0 ("speech understandable with slight effort, occasional repetition required") or DAQ 3.4, because a signal can be strong in dBm yet still be unintelligible.
Why −95 dBm?
−95 dBm is the practical floor at which a portable public safety radio maintains reliable two-way communication on a trunked system inside a building. Below that, the far edge of the cell drops calls, digital P25 audio garbles, and firefighters lose contact in the exact conditions — deep interior, stairwells, basements — where they most need it. The number is measured at the antenna, not the amplifier, so real-world path loss through walls and floors is what the grid test captures.
The DAQ scale
| DAQ | Meaning |
|---|---|
| 1 | Unusable — speech present but not understandable. |
| 2 | Understandable only with considerable effort and frequent repetition. |
| 3.0 | Understandable with slight effort; occasional repetition needed. Common public safety minimum. |
| 3.4 | Understandable with repetition only rarely required. Required by some AHJs. |
| 4 – 5 | Understandable with no or nearly no effort. |
Coverage percentages: 90 % general, 99 % critical
Meeting the signal number in one spot is not enough — the system has to meet it across the building. Code requires roughly 90 % of general building area and 99 % of critical areas to pass. Critical areas are designated by the AHJ and typically include fire command centers, exit stairwells, elevator lobbies and hoistways, fire pump rooms, and other areas essential to fireground operations.
How the grid test works
The AHJ-witnessed acceptance test divides each floor into a grid — commonly 20 approximately-equal squares (some jurisdictions use 40). A technician takes a reading at the center of each square. The floor passes if the required percentage of squares meets the signal-strength and/or DAQ threshold; critical areas are tested to the higher 99 % standard. A single failed critical-area square can fail the floor. The full methodology is covered in ERCES testing services.
Related reference
- NFPA 1225 — the governing emergency services communications standard
- IFC Section 510 — Emergency Responder Radio Coverage in the fire code
- UL 2524 — the ERCES equipment listing standard
- FCC Part 90 — public safety signal booster rules, Class A vs Class B
- ERCES vs BDA vs DAS — what each term means and how they relate
- Ready to scope a project? → JB Technologies ERCES service
Frequently asked
What signal strength is required for ERCES?
A minimum of -95 dBm for both the inbound (donor-to-portable) and outbound (portable-to-donor) paths is the most commonly cited threshold, measured at the antenna. Some AHJs specify a different number or add a Delivered Audio Quality (DAQ) requirement.
What is DAQ in public safety radio?
DAQ (Delivered Audio Quality) is a 1-to-5 scale that measures how intelligible transmitted speech is. Public safety typically requires DAQ 3.0 (understandable with slight effort, occasional repetition) or DAQ 3.4. It captures intelligibility that raw signal strength in dBm can miss.
What coverage percentage must an ERCES achieve?
Approximately 90% of general building areas and 99% of critical areas (fire command center, stairwells, elevator lobbies, and other AHJ-designated areas), verified by a witnessed grid test.
How is ERCES coverage tested?
Each floor is divided into a grid, commonly 20 squares (some jurisdictions use 40). A reading is taken in each square. The floor passes if the required percentage of squares meets the signal-strength or DAQ threshold, with critical areas held to the higher 99% standard.
Can a signal be strong in dBm but still fail?
Yes. A signal can measure adequate power (dBm) yet be unintelligible due to noise, interference, or digital degradation. That is why many jurisdictions require a DAQ (audio intelligibility) measurement in addition to, or instead of, a raw dBm threshold.
Tell us about your ERRCS project
Building address and a rough floor plate is enough to start. We'll respond within one business day with a probability of code-required ERRCS and a budget range.
Talk to JBT about your ERCES project.
Send the building address and a rough floor plate. We'll respond within one business day with a probability of code-required ERCES and a budget range.