P. 57-60 Heed the Warnings
20/11/06
2:44 pm
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Heed the Warnings sounders. Despite the improvements in communication that voice systems can and do bring, sounders and voice systems still communicate using only audible means. To be effective sounders must be audible, in other words at least 6dB above any background noise. however with speech there is the added complication of ensuring the intelligibility or clarity of the message, which is a more complex attribute to achieve and even more difficult to verify on site.
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ASIA PACIFIC FIRE www.apfmag.com
SEE AND HEAR Audible signals alone cannot be effective for all people under all conditions. We have to consider that there are many situations where audibility or intelligibility of alarm signals cannot be achieved; either because people have hearing impairments or the signal is masked by high background noise or perhaps the use of ear defenders. It is neither practical nor safe to make sounders louder and louder to
overcome background noise and indeed increasing volume may aggravate conditions for speech intelligibility, thus additional types of warning devices have be considered where audible units alone will not suffice. If there is a risk that the audible alarms will be ineffective then additional measures are needed that will stimulate other senses, in other words this comes down to sight or touch. (At the time of writing I am not aware of any systems that employ smell or taste as an alarm medium for fire systems, although humans can readily detect and identify fire quite readily using these senses. Smell has been used to give warnings of localised emergencies such as gas leaks or overheated machine bearings, but the debate then becomes whether this is detection of the situation or a warning.) The use of visual warnings (beacons) is becoming more popular as the limitations of using only audible signals is becoming better appreciated. There are however a number of problems in designing systems to use beacons that are not yet properly resolved. Guidance on how to use and apply