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Directional Sounder Dramatically Improves Evacuation Efficiency

For example, at one end of the spectrum consider an offshore oil rig, where everyone present is very well aware of, and is trained to react to the three main audible warnings, each with dedicated tones for evacuate facility, toxic gas or fire. In onshore high risk facilities such as petro-chemical plants, there will be a significant number of office-based personnel who will not necessarily have received the same high degree of training as those whose work gives them direct involvement with the plant areas themselves. Research shows that there is often a considerable delay, caused by uncertainty and the fear of looking foolish, before crowds respond to a genuine warning signal. In industrial facilities, the combination of immediate danger, visibility reductions because of the presence of smoke or other gases and possible reduced illumination from emergency lighting systems if the power has been disconnected, can lead to fear and uncertainty in even the most well-trained personnel.

Traditionally the maps, markings and signage required by the appropriate codes of practice provide the occupants with a visible means for locating a path to safety. Exit signage is usually the primary means for locating an exit, supported by emergency evacuation plans and diagrams showing the locations of, and routes to, the exits. While emergency lighting provides restricted illumination in the event of a power failure, it will be inadequate once the exit routes are filled with smoke. Even if the power supply is not disrupted, the presence of even small quantities of smoke can cause dramatic reductions in the ability to see, reducing people's ability to follow the visual signage. Additionally, in many shopping centres, there are so many notice boards, advertising displays and other visual clutter that the emergency exit signage is often overwhelmed. Many other public buildings have layouts where each floor is visually indistinguishable from any other, and with human nature being what it is, people will not be at all observant about their surroundings.

When defining evacuation requirements, fire engineers assess the RSET (Required Safe Escape Time) against the ASET (Available Safe Escape Time) as laid out in BS PD 7972-6:2004 The application of fire safety engineering principles to fire safety design of buildings - Part 6: Human factors: Life safety strategies - Occupant evacuation, behaviour and condition (Sub system 6). While the ASET may be difficult or costly to improve, it may be more effective to focus on reducing the RSET by exploring new methods of reducing recognition, response and travel times. Two key factors that will reduce a building's evacuation time are persuading people to make efficient use of all available exits and reducing the queuing time at each exit. A system that can intuitively draw people towards the nearest emergency exit may optimise their use, allow travel distances to be safely extended and enable more effective use to be made of the building.

To address the issues of effective premises evacuation, a new directional sound technology, which instinctively attracts people towards its source, has been developed at Leeds University and is now becoming available through commercial partners. The units generate broadband white noise, which is similar to many sounds found in nature to which humans instinctively respond (eg running water, rustling bushes). This type of sound intuitively attracts the listener's attention and draws them towards the source. The white noise, with an amplitude of at least 10dBA above the ambient background level, will cut through the hubbub and be clearly audible. Significant testing has been carried out with this type of sound technology. One such test, conducted in pitch darkness in premises where, because of the location of the building in the side of a hill, the nearest escape route involved ascending stairs from the first floor - a somewhat counter-intuitive action - there were no problems in following the aural guidance and exiting the premises in a very short space of time by the shortest possible route.

The principle is that sound pressure waves arrive at the listener's ears with slight differences in timing and volume depending on the frequency, relative position and distance of the source. The human brain interprets the electrical signals from both ears to give an accurate location for the source: above or below, in front or behind, near or far. By generating broadband noise at low, medium and high frequencies within the audible spectrum, the position of the source can be located with impressive accuracy.

A further enhancement can be added to guide people up and down stairs. It is an intuitive reaction to visualise rising tones as ascending and falling ones as descending; this phenomena is used to good effect in the directional sounder.

In a typical application directional sounders are located at key points in the exit routes, acting as an audible exit sign that helps the building's occupants to pinpoint the nearest exit location and guides them out of the building quickly, reliably and safely, even when visibility is impaired. KAC has developed directional sounders called ExitPoint that generate noise at all frequencies throughout the human hearing range, giving a true broadband, directional sound, the source of which is easily recognised and located by the human ear. The directional sounder is language independent and intuitive, although 15 different language voice-messaging options can also be implemented if required. In tests, exit times can be reduced by up to 75%.

Triggered by the fire alarm control panel or the security system, the directional sounder draws attention to exits and egress routes even in perfect visibility. The varying tones and intensities coming from directional sound devices offer easy-to-understand cues for rapidly finding exits; as soon as people hear the devices, they intuitively take notice of them to find the nearest available exit, thereby reducing exit flow time. In addition to the directional broadband output, different combinations of duty cycles, and rising or falling tones intuitively guide people up or down stairs. As an additional benefit, sound can travel around corners so no direct 'line of sight' is required. In poor visibility, ExitPoint is without equal.

The technology has a number of advantages. In 2005, over 50 people were killed and around 1500 injured in UK non-domestic buildings, with the majority of those injured suffering from the effects of smoke or gas inhalation; the severity of the injuries is normally directly proportional to the time of exposure. In addition to the obvious increased safety performance, the use of directional sound is particularly applicable for installations where the building owner would benefit from a performance-based approach to fire safety. Potential reduced evacuation time may allow the internal layout of the building to be configured for higher occupancy levels or with longer emergency exit paths. By incorporating directional sound in the early stages of building design there may also be opportunities to reduce the need for other fire and emergency systems or reduce risk and insurance costs in buildings or installations fitted with the technology. By ensuring that people will exit the premises through all available routes, rather than everyone heading to the main entrance, there may be the opportunity to improve the use of available space, potentially giving the building owner the opportunity to improve the yield on the property. The relatively low cost of installing the directional sound technology could therefore also have a economic advantage over the lifetime of the building.

Standards covering the technology are starting to emerge: in the UK, BS8456: 2005, Code of Practice for design and installation of directional sounder evacuation systems has been published and a Publicly Available Specification, BS PAS41: 2003, covering performance requirements and methods of testing has been published by British Standards Organisation. Currently, a BSI technical sub committee is reviewing PAS41 and considering whether or not to propose it be developed to become and EN Standard.

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