Plants for sound diffusion for evacuation, also said EVAC plants, include all those devices, which guarantee the correct communication of an emergency, hence for the evacuation of wide spaces, such as schools, malls, hospitals and so on. The acoustic technician is that figure essential to design such plants, since a preliminary acoustic analysis of the space under consideration is necessary, in order to evaluate the size of the needed acoustic treatment. Later, the technician must follow the executive design of loudspeakers’ placement, to be ensured that normative requirements are respected and, at last, he/she must accomplish final check of the installation and annual checks of the plant.

Due to these plants’ importance in relation to people’s safety against some hazards, such as a fire, devices must satisfy European and Italian norms (EN 60849, EN 54, UNI ISO 7240-19), which indicate their proper installation, further than operation and efficiency. 

Though not well known to all, there are a number of fire and / or work safety prevention provisions that explicitly require installation of EVAC systems for the following activities:

• Shopping centers with surface area greater than 1500 m² or height greater than 30 m (DM 10/03/98)
• School buildings class 3-4-5 and with more than 500 people (DM 26/08/92)
  Class 3: schools with from 501 to 800 simultaneous people
  Class 4: schools with from 801 to 1200 simultaneous people
  Class 5: schools with more than 1200 simultaneous people
• Commercial activities with surface area greater than 400 m² (DM 27/07/2010)
• Offices with more than 100 people (DM 22/02/2006)
• Places for public entertainment such as theaters, cinemas, conference rooms etc. (DM 08/19/96)
• Hotel facilities with more than 25 beds (DM 04/09/94)
• healthcare facilities and hospitals(DM 18/09/02)
• Sports facilities with more than 100 audience people (DM 03/18/96)
• Buildings of historical and artistic interest such as museums, galleries, libraries, etc. (DM 20/05/92 n.569 for museums and DPR 06/30/95 n.418 for libraries)
• Metropolitan stations (DM 11/01/88)

Under a technical point of view, norms require that the acoustic technician provides action programs for “acoustically distinguishable areas” (a.d.a.) where some acoustic parameters are explicit, as reverberation time and noise level, in order to calculate and measure the intelligibility indexes STI (Speech Transmission Index) and/or STIPA (Speech Transmission Index for Public Address), defined in CEI EN 60268-16, whose required values are, in a scale from 0 to 1: 

• 0.5 mean intelligibility value measured in each a.d.a.
• 0.45 minimum intelligibility value measured in each a.d.a. 

Within the above-mentioned norms, the acoustic technician can find guidelines of evacuation plant’s design, starting from ranges of acoustic parameters, such as reverberation time, sound pressure and noise levels, going through the placing and correct number of loudspeakers, up to technical features and wiring.

The task of the acoustic technician consists in a measurement during plant’s operational conditions, by using a system, which evaluates the space impulse response, in order to estimate the reverberation time and STI and/or STIPA indexes. Later, those results are reprocessed so that the technician can establish whether an acoustic correction is necessary or not, in conformity with the norm EN 7240-19. In case of complex configurations, an analysis by acoustic CAD could result appropriate, allowing the simulation with several combinations of materials to forecast the behaviour of the space. At last, after all the corrections, a post operam measurement is planned to verify and demonstrate the developed improvements.

Normative reference
The regulatory framework which deals with evacuation systems, their equipment and their installation is identified by three regulations:

• European Standard EN 60849 of April 1998 "Sound systems for emergency purposes", recognized in Italy in 1999 as a standard IEC 60849 "electroacoustic systems applied to emergency services”.
• Since November 2010, UNI has implemented the ISO 7240-19 that has thus become UNI ISO 7240-19 "Fire detection and alarm systems - Part 19: Design, installation, commissioning and service of sound systems for emergency purposes" . The Italian version drawn up in April 2011.
• European Standard EN 54 "Fire detection and fire alarm systems", in particular the parts 2, 4, 16, 24, to which the 7240-19 refers explicitly about the devices that make up the sound system.

Unlike what happened in the rest of Europe, in Italy the 7240-19 is not a replacement for the previous 60849, but rather the two coexist and are applied in two different situations: the first is the reference outlet in case of automatic activation of the evacuation message while the second applies to plants for which a state of emergency activation is still manual. To obviate these problems of overlapping it is currently being edited the norm EN 54-32 which will replace the standard UNI ISO 7240-19.