EMERGENCY WARNING SYSTEMS
SOUND PRESSURE LEVELS ESTIMATION
Following from last edition’s item on the somewhat contentious topic of Speech Intelligibility, this article continues our discussion of Emergency Warning Systems. Sound Pressure Level, while a much older and more mature concept, still occasionally causes unnecessary grief to both the experienced and the uninitiated, especially when it comes to Class 2, 3, and 4 residential buildings. VYACHESLAV (SLAVA) SHARGORODSKY Newsound Fire Services
On 15 June 2019, ABC News published an article with the concerning headline ‘Canberra apartment residents unable to hear fire alarms through soundproofed front doors’. According to the article, residents of a brand-new apartment complex were unable to hear emergency tones from inside their units apparently because of ‘too good’ soundproofing. It concluded that: “ACT Fire and Rescue … found no breaches of the Building Code of Australia. The code does not require that sound levels be tested within units, as long as an alarm of no less than 85 dB is provided at the front door. …. Local authorities told the ABC they were ‘strident for change’, and that measuring 75 dB at the bedhead in apartments was a preferred procedure.”
To measure or not to measure?
The article highlighted only some of the well-known problems with controversial Building Code of Australia (BCA) 36
FIRE AUSTRALIA
ISSUE ONE 2023
concessions for Sound Pressure Level (SPL) measurements in residential building single occupancy units (SOUs) under clause 7 of Specification E2.2a. These have been the subject of numerous heated debates among professionals, both publicly and privately, leading to the following questions: 1. Is it really an acceptable risk to construct a Building Occupant Warning System (BOWS) based on a chain of interconnected simple domestic smoke alarms within a multi-apartment Class 2 building that is not monitored for interconnection faults? 2. Is it reasonable to expect 75 dB SPL at the bedhead, if 85 dB is provided at the SOU front door by a BOWS based on interconnected smoke alarms? 3. Why is 85 dB provided at the SOU front door considered acceptable for BOWS based on smoke alarms, but for BOWS based on loudspeakers, 100 dB at the SOU front door is required? 4. On which side of the SOU front door is the SPL expected to be
measured? (Despite the common assumption that the measurement has to be taken outside the SOU, the BCA is actually silent on the matter.) Unfortunately, this article is too short to provide all technical and historical answers for these issues. To get around these concerns, some practitioners have adopted a common sense, pragmatic approach, taking additional SPL measurements within one or two SOUs of each typical internal layout at the anticipated position of a bedhead with all doors closed, even if 85 dB or 100 dB SPL is achieved at the door providing access to the SOU. This allows them to check whether a minimum SPL of 75 dB is likely to be achieved at the bedhead. If a minimum SPL of 75 dB is not achieved inside the SOU (despite an SPL of 85 dB or 100 dB being measured at the SOU entry door), the follow-up decisions and potential solutions should be discussed with the building certifier, building surveyor, private certifier, and so on appointed for the project.