Crowd Dynamics Ltd - Egress Analysis

Keywords: simulating people, simulating crowds, simulating crowd dynamics, workshops, simulating behaviour, simulating people

It is important to be able to assess the emergency egress times from places of public assembly. It is equally important to quickly identify any locations in an area that may not comply with minimum travel distances to an egress point. The following diagrams are outputs from the Myriad suite which clearly indicate that there are problems in this office which would only be noticed during an emergency evacuation - by then it would be too late!

The process. Import CAD plan (above left - above right). Click on the exit point from this floor. Identify scale (click on two points and enter distance). Run "Spatial Analysis" and the diagram above is produced in a few seconds. The RED areas indicate travel distances greater than, in this example, 30m (note: chosen to illustrate the principle). This takes around 2-3 minutes for the operator to produce a to the Myriad analysis from a CAD plan. We then run an egress route analysis, either by selecting specific start points to test egress widths, or by allowing the system to select N points by cluster, area, at random or from O/D matrix.

The office complies with building codes when empty. However, when furniture is included some areas are found where the travel distance to the emergency exit exceeds the building codes by more than the 2/3 direct distance suggested (horizontal means of escape, section 3, AD B1). These are shown in red in the diagram (above left). These areas include 9.3m² and 17 seats (10% of the population of this floor). The bar graph to the bottom right (above) indicate the percentage of travel distances - the skew in this graph indicates that there areas where congestion will occur (too many equidistant points to the exit).

The implications for insurance purposes and emergency evacuation times are immediately obvious. The software has identified the areas that fail to meet the criteria. This opens the employer/building owner to potential problems for failing to comply with emergency evacuation guidelines and building regulations. It took a few minutes to produce the above result.

This analysis can be taken further. The diagram (above right spatial utilisation analysis) indicates the routes that will experience the highest traffic during an emergency evacuation. Where there are more than two routes converging there will be an additional delay to emergency egress due to congestion. We create a network of these routes and test for "fractality" in that converging paths will create precedence behaviour and add to delays during egress. This method of analysis is also used when testing traffic conditions for car parks and street congestion.

During normal operational use these issue (as described above) would not be apparent however the simulation draws out those features and allows for better understanding of the dynamics of crowds during the emergency evacuation. In addition to the previous analysis we can also test the evacuation paths and times.

The diagram below indicates the distances travelled for a population of 150 people on the floor. Each simulation run starts the population at different places on the floor space and tests the travel distance to the exits. It is clear that this space is not evenly serviced for an emergency evacuation. A simulation using the Simulex program shows the congestion at the convergence points adding to the emergency egress times with the potential to raise the occupants anxiety.

The graph (left) shows ALL variations on egress assuming two of the three emergency exits are blocked (ie: all possible scenarios) highlighting the increased travel distances for a wide range of egress scenarios.

In the diagrams (below) outputs from the Simulex system, the congestion is observed at the convergence points adding to the emergency egress times and the possibility of panic is increased. During emergency egress this can lead to raised anxiety, pushing, panic and increases the potential for falling or tripping. These elements can be reduced with appropriate office layout and design (see optimising offices for further information).



Screen shots from Simulex. When the Simulex system is used in conjunction with the *Myriad* analysis the total picture of how an emergency evacuation procedure may progress can be demonstrated. We use the combination of both of these tools for education and training, for risk assessment and designing for optimal egress.

The outputs from the simulation (above) indicate the typical congestion observed during emergency egress.

The key elements to the Myriad suite for office egress is the speed at which the operator can produce results, test different scenarios and evaluate compliance with the relevant building codes for normal and emergency evacuation. When used with the Simulex software the complete picture of building performance during normal and emergency egress is available. Testing single, multiple or blocked exits paths takes a few minutes and the results highlight the areas that fail the requirements for evacuation.

The results from the simulation show that it takes more than 1 minute 30 seconds to clear this floor - but the people around exit 3 are all clear within 45 seconds. This disproportionate evacuation time is critical in understanding the loading on staircases where the bulk of the evacuation time will be encountered. Queueing on stairs is another aspect of the Myriad system and, in conjunction with the Simulex software, we can assess the delays, exposure, time and total egress times for complex spaces, offer alternative layouts/modifications and quantify risks associated with an emergency evacuation.

It should be noted that the different types of threat (biochemical, bomb threat, phased and directed evacuation) require different strategies. Complex floor layouts all add to the complexity of achieving successful plans and complying with the building codes and regulations. Myriad cuts through all of the complications and produces simple to understand, risk based results and pictorial analysis.

"Canary Wharf is one of Europe's most vibrant, dynamic business districts and prides itself on the quality of environment and service available to its tenants. CWG contacted Crowd Dynamics to assist us in evaluating our public areas for crowd control in a wide range of situations. Crowd Dynamics has an international reputation for developing mathematical models and solutions for various public events. In this case, we wanted a tool to provide a common basis for occupants of the Canary Wharf estate to develop compatible responses to various security and safety related incidents. While the Canary Wharf estate currently has 60,000 staff employed in the development, a robust tool capable of dealing with crowds over 100,000 has been developed in conjunction with our major business tenants. We believe this innovative approach is another first for Canary Wharf and Crowd Dynamics." Anthony Partington (Canary Wharf Managing Director)

Testing the evacuation of a busy London Underground station is a formidable task. Myriad was designed to assess the pedestrian impact for both normal and emergency situations and the diagrams below were produced from both the Simulex/Myriad interface and Myriad running on a CAD plan of the site.

Myriad produces several different types of maps indicating congestion, hesitation points, ingress/egress, circulation and queueing. The model on the right shows the Myriad Level of Service map for a busy station (see diagram below left for the whole area showing the interaction zones (areas where multi-directional flow occurs). The simulation on the left shows how this translates into information. Namely that the areas of highest probability of conflict (red on the right) are those areas where congestion will form in a moving crowd. The advantage of Myriad is that these maps are produces in a few seconds from an AutoCad plan. Click here for further information.

This takes few minutes from a CAD DXF file (below left) imported into Myriad (below right) then click on the Process Image, flood fill and grey scales (each grey scale represents a different height level in the map).

This section of the programme is semi-automated. Using a point and click interface it produces the following maps. We know the physical geometry from the dimensions and can either use demand data (O/D matrix) or assess the capacity of the area from the ingress/egress capacity (physical geometry).

Above - the congestion maps produces in a few minutes using the Myriad point and click interface. Click here for the Level of Service scale. This is the probability of conflict maps and indicates the overall spatial dynamics under normal operating conditions.

Determining the local spatial dynamics we can then run a evacuation model and the superposition of both the spatial dynamics and the egress model highlight those areas we need to focus on for an emergency evacuation.

We can see the congestion points (from a more than normally packed concourse to illustrate the problems in this scenario) and the tight geometry has an impact on the passenger egress. The calculation of egress time, levels of service (normal and emergency evacuation), simulations of the egress in progress and the inclusion of the awareness time (time to start to move) travel distance and egress rates are all part of the Myriad system. See Office Egress for further examples of this technique.

The Myriad suite allow us to test for stability in flow down any route through the system under both normal and emergency situations. The graph below is indicative of a meta-stable system in which the crowd flow is periodic in nature and suffers from high clustering/interactions (ie: a turbulent journey through the system with a lot of stop-start flows). This is indicative of an unbalanced flow system (multiple cross flows, congestion impairing flow, stop/start movement of passengers in the concourse). By highlighting this kind of crowd dynamic we can address the problem during the design phase.

The Myriad suite is highlighting the inefficiencies in the design, namely that there are several "pinch-points" where passengers encounter cross flows and congestion. A more efficient system would sustain a higher peak, have a smoother transition curve and a steep rise and descent (looking like a plateau rather than a mountain ridge). Designing spatial dynamics is a science and this is rapidly gaining momentum with a wide range of multi-disciplinary engineers and consultants around the world.