Audibility and Intelligibility After a Suite Wall Comes Out
A 20,000 sq ft office floor originally had two tenant suites separated by a 12 in. gypsum partition. The wall has been removed to create open plan, and the notification appliances were not changed. You are doing the annual inspection with a sound level meter set to A-weighting and slow response. In the open area, the average ambient is 56 dBA, and a floor scrubber that passes through the space several times a day produces 58 dBA for well over 60 seconds. With the horns sounding, you measure 66 dBA at 15 ft from the nearest horn and at 5 ft above finished floor. In the far corner, the voice system produces a common intelligibility scale score of 0.38. The owner says the alarm is "plenty loud, you can hear it over the scrubber" and asks you to pass the floor.
1. Evaluate the audible measurement against the applicable criteria and state pass or fail with the reasoning.
Read the worked answer
Fail. In public mode, the audible signal must be at least 15 dBA above the average ambient sound level and at least 5 dBA above the maximum ambient sound level lasting 60 seconds or more, whichever is greater.
Average ambient is 56 dBA, so the 15 dBA rule requires 56 plus 15, or 71 dBA. The maximum ambient lasting more than 60 seconds is 58 dBA from the scrubber, so the 5 dBA rule requires 63 dBA. The greater of 71 and 63 is 71 dBA.
The measured 66 dBA is 5 dBA short of the 71 dBA threshold. Note that 66 dBA does satisfy the 5-over-maximum test and would satisfy a naive "louder than the noise" judgment, which is exactly why the two-part rule exists and why the greater value controls. The owner's perception that the horn is audible is not the criterion; the criteria are numeric and measured. Also confirm the measurement conditions are documented: A-weighting, slow response, 5 ft above finished floor, and the horn locations used.
2. The intelligibility score of 0.38 fails. What physical causes would you investigate, and what corrective options would you evaluate?
Read the worked answer
A 0.38 score in a corner of a newly opened floor plan is a design consequence, not a random defect. Removing the partition removed the attenuation that the original speaker layout was designed around, so the corner may now be served by a speaker at excessive distance, at an off-axis angle, or with a direct path blocked by new furniture, a structural column, or a demising return.
Investigate first whether the corner is served at all: pull the speaker circuit drawings and compare designed coverage to the current geometry, then check taps and output levels at each speaker on that circuit. Also check for reflections: a bare hard-lid ceiling and glass partitions produce long delay spreads, and a single loud speaker will not fix that.
Corrective options include adding speakers to reduce the distance to the listener (the most reliable fix), adjusting taps on existing speakers upward where the electronics permit, repositioning speakers that now fire into an obstruction, or adding absorptive treatment where reverberation dominates. Whichever is chosen, re-measure the corner and at least two other worst-case points after the change, and record the instrument, method, and results. Do not pass the area on the basis of a single improved reading.
3. Does the wall removal itself change your obligations as the inspector, beyond reporting the two failed measurements?
Read the worked answer
Yes. The removal of a partition changes the protected-area geometry that the original design was based on. Audibility and intelligibility are now driven by an open plan with different ambient and different speaker-to-listener distances, and the notification appliance layout was never re-evaluated for it. That means the two failed readings are symptoms of an unverified design, not isolated defects, and the report should say so.
Practically: document the change of occupancy configuration, state that the notification appliance layout has not been shown to suit the current floor plan, and recommend that the owner obtain a design evaluation before the corrections are made, so the fix is engineered rather than patched at the two points you happened to measure. Check whether the modification triggered a plan review requirement in the jurisdiction, since a change of this type often does.
On the inspection record, list both measurements as deficiencies with location, instrument settings, and values, and do not issue a passing certification for the floor. Advise the owner in writing that until corrections are verified, occupants in the affected areas may not receive an adequate signal.