VISIBILITY CATCHMENT AREA OF EXITS AND SIGNS

This research project is an attempt to introduce the concept of signage systems into the buildingEXODUS evacuation model so that occupants may dynamically adapt their behaviour in recognition of signage.

Buildings are becoming increasingly complex and this necessitates the incorporation of efficient mechanisms that will assist in navigation and general circulation.  In emergency situations, the ability to navigate efficiently assumes even greater importance.  Evacuation from large complex public building spaces such as shopping complexes, airport terminals, rail stations, entertainment centres, etc is usually hindered by a lack of detailed knowledge of the connectivity of the building space.  In such premises, occupants are usually unaware of the most suitable means of escape.  This is a well know problem with building occupants usually electing to make use of familiar exits, usually the exit with which they entered the building.  Emergency exits or exits not used for normal circulation are often ignored.   In fire situations, where smoke may also obscure vision, the problem is often fatally compounded.  Large scale fatal fires such as Dusseldorf Airport, Stardust disco, Beverly Hills Supper Club, Summerland are examples of situations where the inability to locate efficient means of escape contributed to loss of life.

During general circulation and evacuation people continuously receive visual cues from their environment. The received information exerts an influence on the wayfinding ability of the occupants.  This is dependant on several physical and psychological factors. The number of visual stimuli received from the environment and from other occupants, the location and attentiveness of the occupants, all have an effect to efficient wayfinding.

The presence of signs in an enclosure is essential for aiding and reducing the amount of time spend wayfinding. This is particularly important in large, complex or unfamiliar structures.  Signs act as a source of information that the occupant may not have previously been aware of, in a concise and unambiguous manner. The information relayed provides the occupants with options, suggestions and the opportunity to decide on the best possible route for evacuating an enclosure. In other words a successful signage system can effectively reduce the apparent complexity of an enclosure by increasing the wayfinding efficiency.

It is thus essential to introduce into evacuation models a capability for people to interact with signage systems.

There are a number of physical and psychological factors that influence the effectiveness of a signage system.  These include, visibility of the sign, the likelihood that the occupant will correctly comprehend the message being conveyed by the sign and finally, whether the occupant elects to follow the instructions conveyed.  Important factors that determine the visibility of a signage system and the displayed messages include the location of the sign, size of the sign, the internal configuration of the enclosure, the information quality etc.  Other factors that influence the visibility of the signage system include levels of lighting (both of the sign and the environment) and whether or not smoke is present. Assuming the environmental conditions (smoke levels, obstructions) permit, an occupant may react in several ways following the observation of a sign.  The occupant may misinterpret the information and take the wrong action or decide to ignore the sign.  The occupant may also receive the correct information and either choose to accept it and follow the instructions or ignore it (e.g. security personnel with specific roles during emergencies). All these factors will contribute to the effectiveness of the signage system.

Additionally to the received information occupants continuously identify visually, various features of the enclosure that are essential for wayfinding. Exits, signs, pass ways, concave corner locations are all features that can be identified by occupants as significant points or locations, part of the spatial arrangement of the enclosure, that enable the occupants to take the appropriate decisions and actions to realize their objectives.

First and foremost however, the sign (or feature) must be physically visible to the occupants, if not, the other factors do not have a chance to exert an influence.  In the first phase of this project we concentrate our attention on the visibility aspects of the signage system.  In particular, we introduce into evacuation models the capability to determine the Visibility Catchment Area (VCA) of structural features used for navigation, namely the signage system and the actual physical location of external exits.

The first step is to introduce visibility of exits and signs within the buildingEXODUS evacuation model by defining all the regions in an enclosure from where the navigation feature can be seen.  These regions are identified as the Visibility Catchment Area (VCA).

When determining the positioning of signage systems, the decision as to where to place the signage system may be made when the structure is empty.   Thus, while the signage system is considered compliant to the Code or building regulation, when the structure is fully kited out for use, the signage system may become less effective or even invisible due to furnishings obstructing the signs.   This may also occur when a different internal layout is implemented.  Examples of this may be supermarket, hardware stores or libraries, where high shelving can obscure the view of exits and signage.

Furthermore occupants might lose sight of the exits and signs due to the internal complexity and configuration of the enclosure. For example Airport Terminals are usually populated with numerous signs, some vital for efficient evacuation some for internal circulation and increasingly, advertisements for retail concessions.  The same situation can arise in Supermarkets where the plethora of advertisement and special offers signs together with the shelving might obstruct and hinder the visibility to the exits and to the signs. Apart from the physical issues that these situations produce there are psychological affects as well. The number of signs can create an information overload to the occupants that in turn can inhibit their ability to observe the navigation signs.

Generally there are two approaches to implementing signage visibility.  The most obvious approach focuses on the occupant viewpoint.  In essence this method would simulate the occupant’s vision (and awareness) abilities resolving the issue of whether an individual can see an exit or not.  The alternative approach considers the problem from the sign viewpoint.  With this technique, the region from which the sign is visible is determined. It can be shown that while both methods can produce similar visibility results the latter method is not only more efficient computationally, especially for large population sizes and complicated geometries, it can also be used to determine a range of additional information and statistics.

In the current implementation of the model, the VCA of the exit or sign is determined taking into account the obstruction caused by other signs or structural features.  This takes into account both the size, location and height of the sign and obstructions. For signage systems, the physical extent of the VCA can be terminated according to the local building regulations, for example, a sign based on the standard 15.2cm high letters is legible at a distance of 30m. For increased viewing distance the size of the text legend should be increased proportionally to the viewing distance.

For more information about EXODUS visit the EXODUS Web Pages.  For a complete listing of EXODUS publications visit the FSEG Publications pages.