Hearing the Message – emergency announcements in tunnel noise

Tunnel specifications have been improving in terms of the speech intelligibility required for emergency announcements. To assist, jet fan noise which interferes with achieving intelligibility is generally limited to either 85 dBA or NR85. That may be a hangover from imported practice a couple of decades ago. In long tunnels we can, in any case, avoid using fans near an incident during evacuation. Our experience using our smoke bus in tunnel emergency exercises is that it is the deluge system which most interferes with comprehension of audio messages. We are unaware of deluge noise being considered previously in PA design. Based on detailed deluge noise measurements from five operating tunnels, we substantiate the deluge noise issue and comment on achieving the best intelligibility for in-tunnel emergency messages.