Friday, September 20, 2019
Predictive Capabilities of the Simulex Model
Predictive Capabilities of the Simulex Model Introduction The purpose of this study is to analyse the predictive capabilities of the Simulex model, used to simulate the movement of people in evacuation simulations. Other evacuation models used within the fire engineering community, i.e. Firewind WayOut and simple hand flow calculations, provide quick and easy access to a reasonable estimate for a required movement time for egress in a building. This study will help to reveal whether the additional data used within the Simulex methodology aids the user in reaching a more accurate overall estimate. This will be done by carrying out a number of evacuation scenarios and comparing the results collected using the Firewind WayOut model and hand calculations. A multi storey hotel tower will be used to carry out the study. The outcome of the study will help to calibrate the components of the human behaviour in the Simulex model, as it is suggested that Simulex enables you to simulate occupant behaviour in the event of a building evacuation (IES, Sim ulex simulation of occupant evacuation). A considerable amount of study has been carried out on all aspects of human evacuation from emergency situations, and the affects of human behaviour on evacuation times can be seen as a major factor in terms of life safety. The majority of movement models to date take into account little consideration of the behavioural aspects of the occupants under emergency and focus their work on the flow of occupants. An evaluation of the results gathered in this study will help to show whether Simulex takes occupants-occupants interaction into account. Studies carried out in the past have revealed that occupant evacuation times are highly dependent on their perceived threat of the fire event. Appearance, proximity, propagation, time, and toxic gases of the fire threat also tend to predispose the individual to a higher level of behavioral activity, again depending upon the individuals perception of these threat variables. Thus, occupants located in close proximity to a developing fire, and with clear sensual links with smoke and heat, are likely to react more speedily than those who are reacting solely on alarm signals (John L. Bryan, Human Behavior and Fire). The importance of such an analysis tool is becoming essential in building design as regulation moves to a more performance based system. The purpose of this dissertation is to outline the methodology used within the Simulex model. The outputs determined by each of the models can then be compared along with the hand calculation work carried out. A sensitivity analysis will be performed for the Simulex model and this will help provide a clear evaluation of its predictive potential. Aim To evaluate the predictive capabilities of the Simulex movement model by carrying out both sensitivity and comparative analysis from results gained using the Firewind WayOut movement models and simple hand flow calculations. To gauge the effectiveness of the additional methodological approach taken by Simulex in gaining an overall more accurate estimate. Objectives Carry out a literature review of papers available which cover all aspects of building evacuation. Estimate crowd densities for use as input assumptions for Simulex, Firewind WayOut and hand calculations. Evaluate the model outputs and make a comparison between the methodologies adopted by each of the models. Conclusions should be formed on the basis of this evaluation. Carry out a sensitive analysis of both the Simulex and WayOut models. This can be achieved by altering the user input data to see how this effects the overall evacuation times. Gauge the predictive capabilities of each of the models in terms of how all aspects of building evacuation are taken into account. Investigate how the Simulex model attempts to deal with merging behaviours in a staircase. This will be carried out in reference to the information gained from previous work detailed in the literature review Provide concluding statements with reference to the results gained using the Simulex model. This should include an insight into whether the results gained using this method provide a more accurate estimate of the likely real life evacuation time. Methodology Carry out a literature review of the existing information available which relates to building evacuation and evacuation modeling. Factors to consider include a detailed evaluation of all aspects which affect the evacuation procedures of occupants i.e. affects of alarms, pre-movement times, human behaviour, crowd dynamics, and travel times. A study will be required relating to the current scope of movement models used within the fire engineering community. The methodologies used within the Simulex and the Firewind WayOut models will be studied and form part of the literature review. This will highlight all the differences and similarities between the methodologies incorporated into the tools. This information will be of significant importance when analysing the output data and forming any conclusions. Choose a suitable building design which can be used to carry out the study. The chosen building has been selected as the multi-storey hotel tower, Shibboleth project. Further information of the building will be provided further on in the text. CAD drawings of the Shibboleth hotel tower are required as this design will form the basis of the study. A collection of CAD drawings showing the Shibboleth floor plans will be used as a base to creating these geometries. The CAD drawings will be stripped down (removing inanimate objects i.e. furniture etc) to reveal only boundary layers i.e. walls, floors, etc. These barriers are those in which occupants are unable to pass through. A sensitivity analysis of Simulex and Firewind WayOut models will be carried out. This requires some factor of validation data to be collected by varying single point of input data and analysing how greatly they affect the overall results. By independently altering all the required input data, it is possible to monitor the effect each of the inputs has on the model outputs. This analysis will be carried out for each of the models. Run a mock evacuation using the Simulex model. To achieve this all CAD drawing will be turned into DXF files and inputted into the model. Staircases and floor plans can be linked and occupants will be added relevant to the room sizes as uses (Occupant loading will be calculated for the building and agents will be calculated and added accordingly). Run a mock evacuation using the Firewind WayOut model. The CAD drawings will again be used to measure all lengths and areas in the building. The occupant loading will be kept similar to those used in the Simulex calculation. Carry out hand calculations for the building. The process which will be followed is provided in the SFPE Handbook (SFPE Handbook, Section 3, Chapter 14; Emergency Movement). All input data used will be maintained from the previous work carried out in the computer models. This enables a conclusion to be reached as to whether the innovative tool can be used under the performance based regulatory system and form part of a successful fire engineered solution. Gaining a clear understanding of such information will allow the user to evaluate the results in a more efficient manner. An exhaustive analysis of the output data produced by both movement models will be carried out by the author. A conclusion will then be reached as to whether the FDS+Evac model can provide similar data as the movement model selected as the comparative tool. As this Simulex model is used presently within the fire engineering community to perform evacuation analysis on a number of real projects, it can then be assumed that such a tool supports the engineers performance based design solution. The results will also provide the evidence which will be required to evaluate whether the FDS+Evac model takes into account the threat perceived by the occupants in close proximity to a fire event, and incorporates this into the evacuation time for these occupants. Scope and Limitations Only two models are being reviewed in the study. The university has both Firewind WayOut and Simulex available for use at present and no other models were available at the time this study was carried out. The Simulex model is not used extensively through the course at the university and as a result the user had limited experience in operating it at the time of the study. The modelling work, i.e. measurements of lengths and areas, was carried out entirely from the drawing provided; no site visits etc were made to the building. Only one scenario has been run to carry out the study, a greater timescale for the work would have allowed a more exhaustive study, i.e. greater test cases, to be carried out. As the methodologies in each of the models vary slightly, it was only possible to minimise the extent to which occupant characteristics varied, but it was not possible to eliminate it altogether. Literature Review Regulatory Perspective As architects, designers and engineers continue to push the boundaries of building design, the regulatory system in Scotland continues to move towards a more performance based system. This system allows all parties involved in the design stage a far greater amount of freedom, i.e. promote innovation and limit the impact of regulation (S. Kipp, 1999), when ensuring a building design meets the requirements of the relevant codes. Professionals working within the built environment are now able to incorporate much more of their experience and judgement when developing a design than when following the outdated prescriptive approach, which were conceived for typical buildings. As a result of this, a number of tools have been developed within each discipline which allows each innovative design to be exhaustively tested, ensuring an adequate level of safety is provided before they are incorporated into any building design. For a fire engineer, many of these tools require computational technologies to perform a number of these tasks. Fire modelling is becoming more and more involved in the design stage of many large and complex projects all over the world. A number of models are available, varying in complexity, to carry out any necessary analysis within a number of complex spaces. They allow engineers to evaluate many fire safety related features of a building design before they are finalised, and ensure that any areas of issues with the design can be resolve before a project reaches the construction phase, as altering designs at this point can be extremely expensive and time consuming for all parties. In the UK, the current emphasis for escape design sets out to limit the distance and therefore time in which occupants are subjected to surrounding which will increase the risk of alarm or injury. The current timeframe in which occupants should have to travel from their place or origin and reach a place of safety is 2 minutes 30 seconds. This time had been calculated as a factor of the maximum allowable travel distance and the average walking speed of an occupant. Storey exit widths are sized assuming a specific flow of 80 persons/minute/metre clear width and a flow time of 2.5 minutes (Boyce et al, 2009). The time which is required to clear a floor is an important factor which must be considered to achieve an effective fire safety engineered design. The functional standards allow an engineer to carry out comparative analysis between the required safe egress time (RSET) and the available safe egress time (ASET). A building is deemed to provide an acceptable solution if the time required for egress is less than the time available before conditions are judged untenable by some factor of safety. This requirement is subject to an exhaustive analysis being carried out by a suitable professional, on all aspects of the design which will affect occupant egress. Human Behaviour in Fires A lot of research has been undertaken within the fire engineering community to gain as much understanding as possible of the factors affecting human behaviour when occupants are faced with emergency evacuation procedures in the built environment. John L. Bryan has covered a lot of work studying person-fire interaction and how occupant awareness can affect pre-movement times D. Canter has done a lot of work in gathering data from a number of sources to paint a clearer picture of the evacuation process. E. R. Galea covered a study dealing with human behaviour during evacuation of the world trade centre attack in 2001. Jonathan D Sime has produced work dealing with peoples ability to way find in a building, his work has shown that it may be more effective to incorporate escape routes into the general circulation routes as this will increase occupant familiarity with evacuation routes. Lars Benthorn provided an insight into how people evaluate information and subsequently choose their escape path. There are many more professionals who have done excellent work in analysing human behaviour in emergency situations and all the information collected is useful as it can then be incorporated into the design of evacuation tools. Building evacuation takes on a number of stages and involves a timeframe from the incipient stage of a fire right through until the last occupant has reached a place of safety. Human behaviour can affect both pre-movement and movement times, therefore it is essential to have a clear understanding of how to adapt an evacuation design to maximise its potential in life safety terms. The time to evacuate a building is a combination of several stages, these stages are: Detection time; Alarm time; Pre-movement time, (this is a combination of recognition and response time); and Travel time. The time taken for each of these stages of the evacuation process is dependent on the occupants response and behaviour. Figure 1: Factors involved in assessing the total escape time. (CIBSE Guide E: Fire safety engineering design approaches, 4-7). Pre-movement Time Distribution The pre-movement time of a building is the time for occupants to react to the alarm signal and begin their evacuation process. There are many factors which can affect the pre-movement times of occupants and these will be highlighted later in this text. In multi storey, multiple use occupancies, such as the one selected as part of the study, it can be assumed that not all occupants will have comparable pre-movement times, and for this reason it is good practice to study the appropriate time distribution curves in order to provide an accurate account of an expected pre-movement time in a building simulation. Purser et al, 1999, suggest from their work that Once the first few occupants have begun to move, the pre-movement times for the remainder of the occupants in an enclosure tend to follow a logarithmicÃ¢â¬ânormal frequency time distribution. The shape of the above curves follow a typical pre-movement tome distribution following what has been observed historically; the initial delay of start up highlights the time taken for the first of the occupants to make the preliminary movements towards their chosen exit. This is followed by a rapid increase in frequency as the majority of others tend to initiate their travel phase. The long tail of the curve illustrates the last remaining occupants who will begin their travel period which will signify the end of the total pre-movement phase of the evacuation process. The above distributions are fit well for open plan occupancies where occupants have a clear view of the majority of other persons in the premises. In a building hosting a large number of enclosures, it can be assumed that the time distribution will be far wider than shown in the above diagram. This is due to the limited visibility which would be available for occupants in such a premises; the herding effect as occupants will be reduced as they would have less chance of grouping together and following the actions of the first occupants who move. Purser et al, 1999 , suggests that a range of 20-30 minutes would be more suitable for a multi occupancy building with sleeping risk (such as the Shibboleth hotel tower used to carry out the study). Many different factors will influence how a person will react and the decisions they make will determine their evacuation process. It can be very difficult to obtain real evacuation behavior; real evacuations may be undertaken by people who are unaware of the actual urgency to escape. They may perceive the alarm as a drill (Jake Pauls, 2003) People are often unaware that the alarm they hear is not a false one and so they will proceed to evacuate as they see fit to do so. Stopping to gather up personal belongings or only beginning to evacuate when others around them do. People have both reaction times and pre-movement times, reaction time is the time taken to perceive the alarm and decide to take action; and the pre-movement time is the time that elapses while the occupant is preparing to leave. L. Benthorn (1999): People usually choose to leave a building the same way they came in, even if this is a poorer alternative than other available. Within the field of behavioural science, it is pointed out that people often choose the known before the unknown, which would explain the above behaviour. Occupants in a building will tend to head for the exit them came in through not only are they familiar with this exit it but it will lead them to a place they will recognise. This is particularly true for those people who are not familiar with their surroundings. People will continue to do this and follow the crowd until they are either faced with the fire or are given further information. It has been suggested that incorporating evacuation routes wherever possible into the main circulation routes at the design stage will aim to optimise the effectiveness of the evacuation strategy. This is due to the fact that occupants tend to use a familiar route. The occupant characteristics that should be considered in performing an evacuation analysis are listed below: Population numbers and Density The maximum potential load should be used to give a conservative estimation. The number of people using a building or space and their distribution will greatly affect the travel and flow speeds speed of occupants. Familiarity A persons familiarity and regular use of the building and its systems may cause them to respond differently. Competent users of the building will have prior knowledge of the nearest escape routes and they may have had the opportunity to have participated in drills. Those unfamiliar with the building will rely upon the knowledge of staff and the clarity of signage available, and may be less responsive to warning systems. Distribution and Activities Distribution will impact on movement speeds and density will impact on the ability to communicate instructions. Activities people are involved in will affect their initial response. Those who are dedicated to a task within a building will not necessarily be able stop their job on activation of the alarm system. Level of Alertness The commitment of people to their activity or their interaction with others can affect their awareness. A premise which holds a sleeping risk for occupants can be expected to have a delayed response time. Physical and Mental Ability Some occupants may rely entirely on assistance, disabled; those with a hearing disability or those with a visual disability may require special means of notification. Level of Mobility Affected by the age of occupants, age can influence the ability of an individual to independently make their way along an exit route and reach a place of safety within an acceptable timescale. It may also reduce an occupants ability to withstand exposure to smoke and other harmful bi-products of fire. Social Affiliation Behaviour will be strongly influenced with the interaction between occupants. Groups of people who have a social connection (i.e. parent and child who are separated within premises at the time of the fire event) will try and regroup before making their way to an exit. The time spend undertaking such an act may increase the level of risk for these occupants. Groups of evacuees try to stay together and the slowest member of the group influences their speed. Role and Responsibility Sufficiently, well-trained and authoritative staff will shorten the pre-movement phase of an evacuation process. An effective management plan followed by all members of staff will ensure this is provided within premises. Location Can influence a persons choice of exit and the time to notification. Travel distances will be affected by location. Commitment Those who are committed to their activity will be reluctant to respond to an alarm, especially if it means their task is to be started again. Responsiveness The extent to which a person is likely to respond to alarms, those who have previous experience of emergency situations may be less likely to respond quickly as they are aware of the most appropriate action to take. The Panic Theory When people, attempting to escape from a burning building pile up at a single exit, their behaviour appears highly irrational to someone who learns after the panic that other exits were available. To the actor in the situation who does not recognise the existence of these alternatives, attempting to fight his way to the only exit available may seem a very logical choice as opposed to burning to death. (Turner and Killian 1957) The concept of panic is attributed to occupants lack of knowledge about a fires existence before a fire reaches a size where it can seriously hamper the ease in which evacuees are able to escape. This can be due to a problem with the detection and alarm system installed within premises, or the lack of information available to occupants as they try and make their way to the relevant escape routes. The theory of panic is not an easy thing to define, yet a set of definitions are presented below: A sudden and excessive feeling of alarm or fear, usually affecting a body of persons, originating in some real or supposed danger, vaguely apprehended, and leading to extravagant and injudicious efforts to secure safety. (John L. Bryan 1984) A fear-induced flight behavior which is nonrational, nonadaptive, and nonsocial, which serves to reduce the escape possibilities of the group as a whole, (Kentucky State Police, 1977). In the stress of a fire, people often act inappropriately and rarely panic or behave irrationally. Such behavior, to a large extent, is due to the fact that information initially available to people regarding the possible existence of a fire and its size and location is often ambiguous or inadequate. (Ramachandran, 1990.) Affect of Alarm on Pedestrian Movement The type of detection and alarm system in a building can greatly affect the way in which occupants despond to the emergency signal, and this is turn will affect the response time of occupants. The level of information that occupants are provided with in the early stages of evacuation can influence their decision to evacuate. It has been common practice to use traditional ringing sounders within non-domestic premises in recent years. One drawback of using this form of alarm signal is that occupants are not being provided with any informative information regarding the fire event. Evacuees could benefit from a system which would inform them of a fires location and lets them know which evacuation route is the safest in terms of their location in the building. This is a difficult system to integrate into a building as fires are extremely unreliable and information is specific to a single fire scenario. Sounders themselves are not the most informative method of warning system; they convey little information and have been proven ineffective (Bob Choppen, 2003). Voice alarm systems are largely becoming a more acceptable mode of informing occupants of a fire occurrence in modern buildings. Large premises which are designed to cater mainly for the general public will benefit greatest from a voice alarm system. Occupants are fuelled with much more information of the emergency event than in the past using traditional alarm signals. Voice messages can convey a greater deal of information to the occupants. John L Bryan concluded from his research that the use of voice alarms/public announcements with an alarm bell was the most effective way of warning occupants. Ramachandran in his review of the research on human behaviour in fires in the UK since 1969 summarized the effectiveness of alarm bells as awareness cues: The response to fire alarm bells and sounders tends to be less than optimum. There is usually skepticism as to whether the noise indicated a fire alarm and if so, is the alarm merely a system test or drill? A lack of panic is attributed to a number of factors including: Insufficient seriousness of an emergency. Acceptance of staff responsibility to direct occupants to exits. Evacuation process is complete before occupants have come in sight or contact with fire and smoke. Panic was not initiated at exit paths due to sufficient exit widths being available, thus eliminating the chance for queuing to occur, i.e. little competition for similar exits by occupants. Human Stress Model. (University coursework notes, Evacuation Systems Design model; Powerpoint Presentation namely Human Behaviour in Fire (Slide 48/51), Dr. Iain Sanderson, 2008). Evacuation Modeling Evacuation models can help engineers prove that tenable conditions will be available to occupants for the timescale required for all occupants to reach a place of safety, which an element of safety built in. The total time for occupants for occupants from the time of detection and alarm, to the time for the last occupant to reach a place of safety, is called the Required Safe Egress Time (RSET). This is traditionally compared with the time from fire ignition until tenable limits are exceeded, and conditions have reached a level where humans will be unable to continue their process of escape. This time is called the Available Safe Egress Time (ASET). As long as RSET > ASET by some factor of safety, a building is deemed to provide an adequate level of safety for all occupants to escape in an emergency situation. Pedestrian movement models have typically fallen into two categories, one category dealt independently with movement and the other tried to connect both movement and human behaviour. S. Gwynne (1999) highlights the main approaches available of computer analysis models: Computer based analysis of evacuation can be performed using one of three different approaches, namely optimization, simulation and risk assessment. Furthermore, within each approach different means of representing the enclosure, the population and the behaviour of the population are possible. Movement models can be categorised in a number of forms; Ball bearing, Optimisation, Simulation or Risk Assessment models. Ball bearing / Gaseous This example of movement model treats its subjects as inanimate objects. Sometimes referred to as environmental determinism, subjects are unthinking individuals who respond only to external stimuli, thus human behaviour it not taken into account. Occupants are assumed to begin their evacuation instantly, with no regard to the time taken for detection, alarm and pre-movement times. Factors effecting occupant movement therefore only include physical considerations of the occupants and their surroundings (i.e. crowd densities, exit widths and travel speeds). Individual occupants are merged into units and their movement treats their egress on masse (S. Gwynne, 1999). A good example of a model which employs this type of methodology is Firewind, with its WayOut tool. Optimisation This form of pedestrian movement model deals with large crowds of people at the same time. Evacuees are treated as homogeneous groups, thus there are no independent characteristics for a particular individual. People are uniformly distributed; all exits will be equally shared. One of the best examples of this form of model is EVACNET. 6.5.3 Simulation These models try and take into account not only the physical characteristics of the space, but also consider some representation of human behaviour in emergency scenarios. They attempt to produce as an output the path and decisions taken my individuals during the evacuation process. Examples of this type of model include Simulex and buildingEXODUS. 6.5.4 Risk Assessment Model These models are an attempt to identify hazards associated with the evacuation of a building, be it due to the occupants or the building, and attempt to quantify the resultant risk. An example of this type of model would be Crisp, and WayOut. 6.5.6 Enclosure Representation Enclosure representation of the geometries created within a computer models can take on two forms; fine and course networks. Enclosures are subdivided into a number of zones which are interconnected with neighbouring zones, and the characteristics of each of these affect the parameters found in each on the adjoining cells. The detail and size of each of these zones determines which category a model shall fall into. NODE ARC NODEOne or more arcs connecting 2 nodes are called a Path. (John M Watts 1987). Definition of a network model is given by John M Watts (1987), A network models is a graphical representation of routes by which objects or energy may move from one point to another. 220.127.116.11 Fine Networks Models using this method divide the entire floor space of the enclosure into a selection of shapes or nodes. The size and shape of these nodes will vary for different models. The node is connected to its neighbouring node by an arc. Paths of individuals are tracked over time. Examples of such models include Bgraf, Egress, buildngExodus, Magnetmodel, Simulex and Vegas. 18.104.22.168 Coarse Networks Models following this form of enclosure representation do not allow individual occupants to be followed independently of other within the group. Single nodes represent large spaces, such as rooms and corridors. As evacuees moved from space to space, users will be unaware of their position in each node. A coarse network does not provide information regarding person-wall, person-person and pe
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