Factory sites often contain many risk factors. In history many infernos and other major calamities have happened at factory sites. Evacuation systems are effective systems. However, the reality is often different. There are only a few regulations and guidelines. There are often only evacuation procedures regulated for the main building.
If we take a critical look at the current standards and guidelines, then there is much material available to produce good guidelines with reference to the current standards. It is important to pay a lot of attention on the audio quality. Consider the volume level and above all the STi values; speech intelligibility.
The sound of a speaker is called a point source and we can assume that the noise decreases with each doubling in distance by 3dB. In an outdoor situation we are, however, dealing with reflections and drift of sound, so in a projection this must be taken into account. Assuming we use high power speakers of at least 120dB, then in an ideal situation, there is still 93dB sound at a distance of 500m.
However, the reality is different, i.e. much lower numbers by external influences, so it seems to matter to place the broadcasting points 200 to 250 meters apart from each other. Reasonably you could surely keep 90dB sound at a distance of 200 meter in this situation and transcend the environmental noise which is usually about 80dB.
Emergency services are then able to do voice communications and thus keep the evacuation under control. This is still an important issue.
‘Panic can be prevented, or at least reduced, if people are well-informed’
An evacuation system consists of a logic part with audio amplifiers and speakers. Due to the often large distances in factory areas preference will already be given to decentralized master/slave configurations at an early stage of the design. The practice is that at the design stage system cabinets are placed on the speaker locations with audio amplifiers and power supplies to be used in evacuation systems. These evacuations centrals will be controlled from one central point.
The transmission paths will preferably be redundant. You can consider this as a wish. On connections based on IP, for example internet connections, this is already a lot harder. Good solutions can be made for correct system specifications.
‘It is also important to pay much attention to the power supplies in such systems’
The EN54-4 A2 requirement, as stated in the fire alarm domain, is actually the most obvious solution. The requirements for reliable performance are described for both the power supply unit as the secondary power supply with batteries.