answering Part A ,B by getting the solution (find the attached documents )

Anonymous
timer Asked: Nov 15th, 2016

Question description

a brief :

there is two floors , and fire will happen in the middle of the room , there is two exits and you have to count the time . it is all explained in the attached docs

* i will attach the assignment structure for yourself that you should stick to word by word .

* it should be based on United kingdom standard.

* i will also attach examples that my friends did last year but they didnt get good grade , i want you to follow their structure but try your best to get me higher marks .


the question :

Part A – 50%

  • On the basis of the plans and information provided below determine the Required Safe Escape Time (RSET) from the MEZZANINE area following the guidance of BS7974 (i.e. perform the RSET part of an ASET-RSET calculation).
  • Provide a commentary alongside the calculation that discusses the calculation process and explains each of the different terms/elements used, their importance and provide justification for your choice.

Part B - 50%

  • For the same case explain how the Available Safe Escape Time (ASET) could be determined. You should discuss the different approaches that could be used, potential design fire scenarios and the criteria (e.g. Tenability limits) that could be used to determine the ASET. Please note that an actual ASET calculation is not a requirement of this assignment.

Scenario

When answering Parts A and B above the following information should be used:

  • The area in question is a storage warehouse for building materials (which may include combustible materials).
  • The building will have dimensions 60m by 52m by 14m high (See Figure 1).
  • The building will have two exits (each 1.8m wide) from the ground floor (See Figure 1).
  • The building will only be accessed by trained staff and not members of the public
  • The owner of the warehouse wants to add a mezzanine floor (see area in red on Figure 2).
  • The floor of the mezzanine will be located 9m above the ground floor level.
  • The mezzanine will be occupied by up to 20 members of staff and there will be no disabled access.
  • A single open stair (1.8m wide) will be the only way to access/exit the mezzanine (see Figure 2).
  • Important note: the plans do not show the location of storage/obstacles. You should ensure that your calculations/discussion etc. take account of this.

( the picture is attached with the same details in the folder of the structure )

The word limit is 1,500 words (+/-10%) for each part of the assignment. This excludes footnotes but includes quotations. The word count must be printed on the top right hand corner of your work.

Remember:

  • You must answer the question set
  • You must keep to the word limit of 1,500 words for each part
  • You must demonstrate that you have met the learning outcomes
  • As you construct and present your work, consider the assessment criteria

Presentation Instructions

It is your responsibility to ensure that your work is neatly and accurately presented.

The work must be:

  • Word-processed
  • Single sided
  • 1.5 or double line spaced
  • Ariel 12 point font
  • Justified
  • Page numbered
  • On A4 paper
  • Margins left and right 3cm
  • Attached to a cover sheet.

Marks may be deducted for failure to follow these instructions. Please look at the Student Guide to Assessment for more information.

Referencing

All academic writing must be referenced. If you use other people’s ideas without referencing them you are plagiarising their work.

Either:

Use the Harvard system of referencing within your text. This will take the form: surname, year of publication, page number, and is enclosed within brackets, for example (Bradley 1998, 277). At the end of your essay you should provide an alphabetical list of all the works you cite

Or:

Use the Numeric System of referencing within your text. At every point in the text where a reference is made, insert a number (in brackets or superscript) and then list the references numerically at the end of your work.

Plagiarism

The use of work produced for another purpose by you, working alone or with others, must be acknowledged.

Copying from the works of another person (including Internet sources) constitutes plagiarism, which is an offence within the University’s regulations. Brief quotations from the published or unpublished works of another person, suitably attributed, are acceptable. You must always use your own words except when using properly referenced quotations.

You are advised when taking notes from books or other sources to make notes in your own words, in a selective and critical way.


please note i want you to follow the folder i attached as " the assignment structure " as it has the picture of the question in details. also review the attached file as an example

UCLAN FIRE www.uclan.ac.uk/fire University of Central Lancashire School of Engineering FV3201 Individual Assignment Brief Assignment Details This assignment is based around the principle of ASET-RSET and guidance provided in BS7974. You must therefore utilise BS7974 and the relevant Published Documents that support BS7974 to answer this assignment. Part A – 50%  On the basis of the plans and information provided below determine the Required Safe Escape Time (RSET) from the MEZZANINE area following the guidance of BS7974 (i.e. perform the RSET part of an ASET-RSET calculation).  Provide a commentary alongside the calculation that discusses the calculation process and explains each of the different terms/elements used, their importance and provide justification for your choice. Part B - 50%  For the same case explain how the Available Safe Escape Time (ASET) could be determined. You should discuss the different approaches that could be used, potential design fire scenarios and the criteria (e.g. Tenability limits) that could be used to determine the ASET. Please note that an actual ASET calculation is not a requirement of this assignment. Scenario When answering Parts A and B above the following information should be used:  The area in question is a storage warehouse for building materials (which may include combustible materials).  The building will have dimensions 60m by 52m by 14m high (See Figure 1).  The building will have two exits (each 1.8m wide) from the ground floor (See Figure 1).  The building will only be accessed by trained staff and not members of the public  The owner of the warehouse wants to add a mezzanine floor (see area in red on Figure 2).  The floor of the mezzanine will be located 9m above the ground floor level. 1 UCLAN FIRE www.uclan.ac.uk/fire  The mezzanine will be occupied by up to 20 members of staff and there will be no disabled access.  A single open stair (1.8m wide) will be the only way to access/exit the mezzanine (see Figure 2).  Important note: the plans do not show the location of storage/obstacles. You should ensure that your calculations/discussion etc. take account of this. 52m 60m Figure 1 – Ground floor plan of warehouse 2 UCLAN FIRE www.uclan.ac.uk/fire Mezzanine Open stair* 12m 20m *Note: Arrow on stairs indicates travel upwards Figure 2 – Proposed mezzanine arrangement 3 UCLAN FIRE www.uclan.ac.uk/fire The word limit is 1,500 words (+/-10%) for each part of the assignment. This excludes footnotes but includes quotations. The word count must be printed on the top right hand corner of your work. Remember:     You must answer the question set You must keep to the word limit of 1,500 words for each part You must demonstrate that you have met the learning outcomes As you construct and present your work, consider the assessment criteria Presentation Instructions It is your responsibility to ensure that your work is neatly and accurately presented. The work must be:  Word-processed  Single sided  1.5 or double line spaced  Ariel 12 point font  Justified  Page numbered  On A4 paper  Margins left and right 3cm  Attached to a cover sheet. Marks may be deducted for failure to follow these instructions. Please look at the Student Guide to Assessment for more information. Referencing All academic writing must be referenced. If you use other people’s ideas without referencing them you are plagiarising their work. Either: Use the Harvard system of referencing within your text. This will take the form: surname, year of publication, page number, and is enclosed within brackets, for example (Bradley 1998, 277). At the end of your essay you should provide an alphabetical list of all the works you cite Or: Use the Numeric System of referencing within your text. At every point in the text where a reference is made, insert a number (in brackets or superscript) and then list the references numerically at the end of your work. 4 UCLAN FIRE www.uclan.ac.uk/fire Plagiarism The use of work produced for another purpose by you, working alone or with others, must be acknowledged. Copying from the works of another person (including Internet sources) constitutes plagiarism, which is an offence within the University’s regulations. Brief quotations from the published or unpublished works of another person, suitably attributed, are acceptable. You must always use your own words except when using properly referenced quotations. You are advised when taking notes from books or other sources to make notes in your own words, in a selective and critical way. Submission Your work must be submitted with a front cover sheet (detailing the module code and title, essay title, student name and reference number, word count, date submitted). The assignment should be submitted electronically before 4.00pm on the given date via Turnitin (a guide to submitting work via Turnitin can be found on Blackboard). Learning outcomes This assessment will test your ability to meet the learning outcomes as described in your module booklet, specifically: 1. Demonstrate critical thinking and problem solving 2. Exhibit creativity and innovation in technical design 3. Critically review and analyse client and user requirements, technical briefs and apply significant knowledge to design scenarios, including relevant technological, engineering, legal, health and safety and development factors Assessment Criteria For more information please see the marking guide at Appendix 1 5 UCLAN FIRE www.uclan.ac.uk/fire Appendix 1 Marking Scheme Part A B Criteria Example Mark Report Presentation Report Content Presentation, layout, spelling and grammar, formatting quality, referencing etc. Appropriateness and depth of content etc. Logical structure. Accuracy and complexity of example calculations. Quality of discussion, analysis and conclusions. Presentation, layout, spelling and grammar, formatting quality, referencing etc. Appropriateness and depth of content etc. Logical structure. Accuracy and complexity of example calculations. Quality of discussion, analysis and conclusions. 5/50 Report Presentation Report Content 6 45/50 5/50 45/50
School of Forensic and Investigative Sciences Assessment Coversheet Module Code Module Title Student’s name Student ID Number Course/ Subject Assignment Title/ Number FV3201 Module Tutor Engineering Design Project Dr. Paul Currie G BEng Fire Engineering (Hons) FV3201 Engineering Design Assignment Project Individual ‘I confirm that this piece of work which I have submitted is all my own work and that all references and quotations from both primary and secondary sources have been fully identified and properly acknowledged in footnotes and bibliography.’ Signature: Date: December Submission 3,2015 Deadline Extension Agreed date: Extension Agreed by: Work submitted should be presented in the following format:  Double line-spaced, on A4 paper  In Arial or Times New Roman font in black ink December 4,2015 Grade* Learning Outcomes To be completed Module Tutor Feedback by the student Practicing real engineering problem solving with specific standards How to deal with design and using worst case scenarios Brief knowledge of different methods in engineering design General comments: Strengths: Areas improvement: for If there is something you do not understand or some aspect on which you want further information, and you have not yet had the opportunity, you must make an appointment with your tutor to discuss this assessment and the feedback given. You may be asked to use this feedback to reflect upon your personal development (PDP). Upon receipt of the feedback from your module tutor, please complete below your reflections on this assessment for your future action. 1st Marker Signature Date Moderation signature** Date UCLAN FIRE www.uclan.ac.uk/fire ENGINEERING DESIGN PROJECT Individual Assignment DECEMBER 3, 2015 DR. PAUL CURRIE University of Central Lancashire UCLAN FIRE www.uclan.ac.uk/fire Table of Contents INTRODUCTION 1 PART A 2 RSET INTRO TIME FROM DETECTION TO A GENERAL ALARM TOTAL TIME OF EVACUATION PRE-MOVEMENT TIME TRAVELLING TIME TIME FROM IGNITION TO DETECTION FINAL RSET 2 2 3 3 4 8 9 PART B 10 INTRODUCTION TENABILITY AND WILLINGNESS TO ENTER OR ABILITY TO MOVE THROUGH SMOKE ASET CALCULATIONS ASET EQUATION ZONAL MODELLING CFD MODELLING 10 11 12 12 13 14 REFERENCES 16 Figure 1 fire placement _________________________________________________________________ 5 Figure 2 escape trip ____________________________________________________________________ 6 UCLAN FIRE www.uclan.ac.uk/fire Introduction This assignment contain two parts, both of them can be taken from the same British Standard BS7974 based on the ASET-RSET principle. The first part is about determining the Required Safe Escape Time (RSET) for a new warehouse mezzanine area by using special equations conducted from the standard with the explanation, while the second part is about explaining how to determine the Available Safe Escape Time (ASET) with different methods without the calculation part for the same scenario. Keeping in mind the following information are provided by the assignment brief: - The warehouse dimensions are 40m by 32m by 12m high. - A mezzanine will be located 8m above the ground floor. - 15 trained staff members can occupy the mezzanine. - There will be only one open staircase to the mezzanine. 1|Page UCLAN FIRE www.uclan.ac.uk/fire Part A RSET Intro RSET is a calculated time that is required for the occupants of a specific area to escape to safety from the moment of ignition. (British Standards, 2004) A general equation obtained from the BS7974 will be used to calculate RSET. 𝑡𝑅𝑆𝐸𝑇 =∆𝑡𝑑𝑒𝑡 + ∆𝑡𝑎 + (∆𝑡𝑝𝑟𝑒 + ∆𝑡𝑡𝑟𝑎𝑣 ) (British Standards, 2004) tRSET = Required Safe Escape Time (s). ∆tdet = Time from Ignition to Detection (s). ∆ta = Time from Detection to a General Alarm (s). ∆tpre = Pre-movement Time for the Enclosure or Building Occupants (s). ∆ttrav = Travel Time of the Enclosure or Building Occupants (s). Following this, a number of equations must be used to conduct the components of this main RSET equation. Time from Detection to a General Alarm ∆ta = 0 assuming level A1 alarm system where an automatic detection throughout the building will immediately triggers a general alarm to all parts of the building, so that means the time from detection to a general alarm will be taken as 0s. (British Standards, 2004) 2|Page UCLAN FIRE www.uclan.ac.uk/fire Total Time of Evacuation Since there is low occupants density in the warehouse due to the category of the design behavioural scenario and occupancy type as awake and familiar, (British Standards, 2004) then there will not be any queuing in front of the exit that means no need to calculate the occupant flow time. The total equation time will be consists of two parts: ∆𝑡𝑒𝑣𝑎𝑐 = ∆𝑡𝑝𝑟𝑒(1𝑠𝑡 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒+99𝑡ℎ 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒) + ∆𝑡𝑡𝑟𝑎𝑣(𝑤𝑎𝑙𝑘𝑖𝑛𝑔) (British Standards, 2004) Pre-movement Time The pre-movement time is divided into two parts: 1st percentile pre-movement is the period between the beginning of the general alarm and the movement of the first few occupants, while the 90th percentile premovement is the period between the movement of the first few occupants and the movement of the last few occupants. (British Standards, 2004) In this specific scenario awake and familiar occupants (the building can be accessed by trained staff only), the warehouse criteria is M1 B1 A1, where: Management Level M1: the occupants are trained to fire safety management. Building Level B1: a simple rectangular single storey building With a simple layout with clear visual access and exits leading to outside of the building. Level A1 Alarm System: automatic detection throughout the building, trigging immediate general alarm. (British Standards, 2004) For known these categories, a value for the pre-movement time can be obtained from its table: (British Standards, 2004) ∆𝑡𝑝𝑟𝑒 = ∆𝑡𝑝𝑟𝑒(1𝑠𝑡 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒) + ∆𝑡𝑝𝑟𝑒(99𝑡ℎ 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒) 3|Page UCLAN FIRE www.uclan.ac.uk/fire ∆𝑡𝑝𝑟𝑒 = 30 + 60 = 90 s The total pre-movement time from the general alarm to the last few occupants is 90 seconds. Travelling Time ∆ttrav(walking) which is the required time for occupants to walk to an exit that leads to an escape way. (British Standards, 2004) ∆𝑡𝑡𝑟𝑎𝑣(𝑤𝑎𝑙𝑘𝑖𝑛𝑔) = 𝑡𝑟𝑎𝑣𝑒𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑤𝑎𝑙𝑘𝑖𝑛𝑔 𝑠𝑝𝑒𝑒𝑑 Walking speed is 1.2 m/s, assuming that there is no smoke density at the beginning due to the efficiency of the detection system so the visibility will remain unaffected. (British Standards, 2004) 4|Page UCLAN FIRE www.uclan.ac.uk/fire Travel distance: for this part, a fire placement must be considered in front of one of the exit doors to make it as the worst case scenario. (figure1) 32m 40m Figure 1 fire placement 5|Page UCLAN FIRE www.uclan.ac.uk/fire And also considering worst case scenario in the travel trip as the travel distance which is the longest possible distance from the available exit. (figure2) 28m 10m 21m Mezzanine 10m 25m 15m Figure 2 escape trip 6|Page Open stair* 8m UCLAN FIRE www.uclan.ac.uk/fire Travel distance in plan = 28 + 25 +10 +21 = 84m Assuming there will be obstacles on the escape route that will add approximately 50% in addition to the straight lines distance, so the real travel distance will be: Travel distance = 84 + (84/2) = 126m So, ∆𝑡𝑡𝑟𝑎𝑣(𝑤𝑎𝑙𝑘𝑖𝑛𝑔) = 𝑡𝑟𝑎𝑣𝑒𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑤𝑎𝑙𝑘𝑖𝑛𝑔 𝑠𝑝𝑒𝑒𝑑 = 126 1.2 = 105 s The total time for the farthest occupant to reach the safe exit is 105 seconds. ∆𝑡𝑒𝑣𝑎𝑐 = ∆𝑡𝑝𝑟𝑒 + ∆𝑡𝑡𝑟𝑎𝑣(𝑤𝑎𝑙𝑘𝑖𝑛𝑔) = 90 + 105 = 195 s The total evacuation time for all the occupants is 195 seconds. 7|Page UCLAN FIRE www.uclan.ac.uk/fire Time from Ignition to Detection Last part taking the assumption of the minimum fire size for the detection process to calculate the detection time ∆tdet by using couple of equations to get the heat release rate then get detection time at the end. Q = α (t - ti)2 (British Standards, 2003) Assuming that there is no time of ignition, ti = 0 seconds Q = is the total heat release rate from the fire during the growth phase (kW). t =is the time from ignition (s) = ∆tdet α = is the fire growth parameter (kJ/s3). The warehouse is considered as an industrial storage building, so the fire growth rate will be ultra-fast, and that means α = 0.188 kJ/s3. (British Standards, 2003) Next, using the ceiling jet to get the heat release rate Q: r/h =5.3/12 = 0.44 > 0.18, so 𝑇𝑗𝑒𝑡 − 𝑇0 = 5.38𝑄 2⁄ −1 3ℎ (CIBSE, 2003) r = is the horizontal distance between the fire axis and the fire detector (m). h = the ceiling height (m). T0 = the ambient temperature = 20 °C Q = is the total heat release rate from the fire (kW). Tjet = is the jet temperature (°C). Tjet = Tdet (detection temperature) = 68 °C, to get the minimum fire size. After that, re-arrange the equation to get the total heat release rate: 𝑄={ (𝑇𝑗𝑒𝑡 −𝑇0 )ℎ 5.38 8|Page 3⁄ 2 } ={ (68−20)12 5.38 3⁄ 2 } = 1107 kW UCLAN FIRE www.uclan.ac.uk/fire The total heat release rate is 1107 kW. Finally, re-arranging the first equation and applying the new value of Q to get the detection time: 𝑄 1107 ∆𝑡𝑑𝑒𝑡 = √𝛼 = √0.188 = 76.7 s The time from ignition to detection is 76.7 seconds. Final RSET In the end, putting all the calculated values in the main RSET equation to get the required safe escape time: 𝑡𝑅𝑆𝐸𝑇 =∆𝑡𝑑𝑒𝑡 + ∆𝑡𝑎 + (∆𝑡𝑝𝑟𝑒 + ∆𝑡𝑡𝑟𝑎𝑣 ) 𝑡𝑅𝑆𝐸𝑇 = 76.7 + 0 + (90 + 105) = 271.7 s The required safe escape time for the warehouse is 271.7 seconds. 9|Page UCLAN FIRE www.uclan.ac.uk/fire Part B Introduction In majority of cases involving fire, evacuation takes centre stage. The basic underlying principle of the performance based building design is the available safe escape time (ASET) should be greater than required safe escape time (RSET) by a desirable margin of safety. In setting the appropriate margin of safety there is consideration of the risks that are associated with various potential fire situations and also the fact that ASET and RSET for any design has inherent uncertainty. In an ideal fire safety design it is to be ensured that the occupants of a building are to be able to reach a safe area without being into contact or even being aware of heat generated by the fire or its effluent. This design criterion should be the major centre of focus in multi-compartment buildings if the safety of the majority of the occupants of this building is to be ensured (BS 7974 and BS ISO/TR 13387-8). This means that the major design criterion involves estimation of the time required for occupants to make their way to a point of safety where the situation at hand is that the occupants are not directly affected by heat of effluent. Where the occupants are in enclosure where the fire is originating from, there will be high chances that this group will be aware or will be exposed the fire effluent. The bulk of combustions products compost of carbon dioxide and water usually will have highly toxic gases mostly carbon monoxide and to some extent they may include hydrogen cyanide and some other rare gas species. The products of combustion that are in solid or liquid form will bring about reduced visibility in the smoke, which is an additional problem that is brought about by the smoke. The occupants that could be trapped in the building might suffer from suffocation due to the reduced level of oxygen brought by the combustion process. The heat generated by the combustion products may be another hazard to those in the building as they are likely to be immersed in the smoke or the heat may reach them through thermal radiation with the hot smoke layers being the source. 10 | P a g e UCLAN FIRE www.uclan.ac.uk/fire Tenability and willingness to enter or ability to move through smoke In a building, if the situation is such that smoke is mixed down almost to the level of the floor, the this could mean that while some of the may be willing to pass through the dense smoke, but some of the occupants may not be willing to make their entry into escape routes that appear to be full of smoke and instead this occupants may turn back or they may not in a position to locate the exit. For scenario where heat has not risen considerably to a level of raising any form of concern, then the initial effects of smoke will depend of visibility distance and the irritating effects that come as a result of the occupants’ direct exposure. Research findings has shown that close 30% of people will make a decision of turning back instead of making their way through areas that are full of smoke (Bryan, J.L.,1995; Wood, P.G.,1972) and the visibility level that will result to people turning back is of three metres. The optical distance is 0.33 (D.m-1) and extinction coefficient of 0.76 with women being reported to turn back more than men. The behaviour exhibition will also be depend on whether layering give the people a chance of crouching down so as to reach a level where smoke intensity is relatively low or whether there is low placed lighting that could enhance visibility. Putting all this into consideration with respect to parameters that includes size and how complex the building is, design limit with regards to optical density of smoke will be used. BS 7899-1 and BS 7899-2 is a good guide on how this is to be accomplished. (Yuan, 2001; p123) For approximation sake, the assumption could be that occupants will not enter an escape route that has a visibility of less than 3 metre (D·m–1 = 0.33), extinction coefficient (0.76). But where this happens and the ability of them progressing will depend on optical density and irritancy of smoke. 11 | P a g e UCLAN FIRE www.uclan.ac.uk/fire ASET calculations For ASET there must be some considerations for the time and for the conditions that could happen in any building enclosure. The unexpected conditions could might happen with a too late prediction from the occupants of the building, so they might not survive in these fire hazards like smoke density (visibility), toxicity (toxic substances due to combustible materials), temperature (heat flux). (Poreh,2000: p81) When occupant get exposed to these hazardous scenarios, their mental and physical abilities might effect on the occupants expected escaping time, which would cause some harmful injuries more even fatalities in the worst case scenario. ASET Equation     1   2 2  3  A f .αHRR  3 .ρ a     α HRR .ASET 5 3 3      LLH  H  1  ASET  1     2   3H  LLH A f .c p .353    ρ a2 g  3    0.21   c T   p a   (Tosolini et al., 2013, 223-228) Where: H is the hight (m). Af is the area (m2). Pg is the density of the upper layer (kg.m3). Pa is the density of air at the temperature of air Ta (assuming a constant of 293 K). cp is the specific heat (1 kJ/kg/K). g is the gravitational constant (9.81 m/s2). αHRR is the growth rate factor for t2 fires (kW/s2). 12 | P a g e 3 5 UCLAN FIRE www.uclan.ac.uk/fire Zonal modelling One zone model may not be sufficient in addressing the range problems at hand due fact that they have basis on some assumptions which are made according experience and the observations made with regards to the way fire develops for any particular environment. Heat content of the plume is given by 𝑄𝑃 = 𝜒𝑄 Where 𝜒 is the fraction of total heat release is lost through convection ranging from 0.4 to 0.9; 𝑄𝑃 is heat release rate convected from the plume and 𝑄 gives the overall heat release from the fire source Other zone model expressions are where 𝑧 > 5𝐷𝑠 and the smoke mass flow rate at a distance of z from fuel surface is given by 1 𝑚𝑠𝑚𝑜𝑘𝑒 = 0.071𝑄𝑃 3 (𝑧 − 𝑧𝑜 )5/3 (PD 7974-2:2002 p 21) Where 𝐷𝑠 represents the source linear dimensions; z represents the plume height above fuel surface, 𝑧𝑜 gives the virtual source above the fuel surface while 𝑄𝑃 represents the heat output of fire through convection. Air mass flow rate of the air that is inside the fire is given by 𝑚𝑎𝑖𝑟 = 0.19𝑝𝑧 3/2 (PD 7974-2:2002 p 21) Where p represents the perimeter of the source. 13 | P a g e UCLAN FIRE www.uclan.ac.uk/fire CFD Modelling Computational fluid dynamics (CFD) using developed techniques to produce a fluid dynamics simulation. CFD helps in having a solution for any of the time-dependant equations that are related to the laws of conservation using numerical methods. Due to the high level development and complexity of the CFD modelling, the computer must have sufficient speed and memory size to do the simulation perfectly. When comparing the CFD modelling with the zonal one, the CFD costs more and it is complex, but it is more useful for a wider applications and scenarios and it does not depends on obvious assumption as the zonal modelling. In CFD the basic equation that is set in simulation of fires in enclosures is given by 𝛿 𝛿𝑡 (𝜌𝜙) + 𝛿 𝛿𝑥𝑗 𝛿 𝛿𝜙 (𝜌𝑢𝑗 𝜙) = 𝛿𝑥 (Γ𝜑 𝛿𝑥 ) + 𝑆𝜑 (PD 7974-2:2002 p 36) 𝑗 𝑗 Where 𝜙 is a generic variable which may represent 3 Cartesian velocity components 𝑢𝑖 , enthalpy (h) or the fraction mass of a particular species (𝑌𝑖 ). Here, the mass continuity representation is given by 𝜙 = 1. 𝑆𝜑 is a source term that should be appropriate to 𝜙 that may incorporate for instance the effect of chemical production and radiative heat losses. While Cartesian grid may not be essential its assumption serves simplicity. With all dependant variables in the previous equation being time averaged quantities and neglecting fluctuations in density, thus we have 𝒖𝒊 = 14 | P a g e ̅̅̅̅̅ 𝝆𝒖𝒊 𝝆 UCLAN FIRE www.uclan.ac.uk/fire There is incorporation of the turbulent and molecular diffusion in the diffusion term by the exchange of Γ𝜑 . Usually in majority of CFD models the assumption is that Reynolds stresses and scalar fluxes that involves correlations of the fluctuating properties, may be modeled through engagement of gradient transport hypothesis expressed as 𝜌̅ . ̅̅̅̅̅̅ 𝑢𝑖′ ∅′ = −Γ𝜑 𝛿𝜙̅ 𝛿𝑥𝑖 Where 𝑢𝑖′ gives the fluctuating component of velocity while ∅′ is the generic variable. In order for the local value to be determined for Γ𝜑 there will be need to have solution for transport equations for 𝜅 which is the turbulent kinetic energy and also a solution for 𝜀 which is the rate of dissipation (Milter, 1991 p711). There is also need to give special attention to effect of buoyancy with regard to extra turbulence production for the case of rising plume and inhibition for the case of stratified layers. Then the conservation models are discretized and the solution obtained through iteration on a numerical grid many control volumes in the range of hundreds of thousands to millions that will fill the computational domains a process that employ the ‘guess and correct operations’. By having solutions of the equations with the relevant boundary conditions being put in place, the major features of a smoke motion problem for a fire of known size can sufficiently be captured (Miles, 1997; p 237). However, in CFD modelling incorporating the combustion model is of great importance when it comes to modelling extended release heat over a volume whose determination is through the local mixing conditions. Caution should be taken before one makes their mind of representing a fire by a heat source if one is in doubt of the resulting consequences. 15 | P a g e UCLAN FIRE www.uclan.ac.uk/fire References British Standards, 2003. PD 7974. Application of fire safety engineering principles to the design of buildings: Intiiation and development of fire within the enclosure of origin, Volume 1, pp. 25,26. British Standards, 2004. PD 7974. The application of fire safety engineering principles to fire safety design of buildings: Human factors: Life safety strategies-Occupant evacuation, behaviour and condition, Volume 6, pp. 5,7,8,9,10,11,12,15,21,25,36. CIBSE, 2003. Fire Engineering CIBSE Guide E. In: The Chartered Institution of Building Service Engineers. London: s.n., pp. 10-13, 10-14. Miles, S. , Kumar, S. and Cox, G. (1997). The Balcony Spill Plume-some CFD Simulations, pp 237-247, Proc 5th International Symposium on Fire Safety Science, IAFSS. Mitler , H E. (1991).Mathematical Modelling of Enclosure Fires-Numerical Approaches to Combustion Modelling, p711 Progress in Astronautics and Aeronautics, 135,1991. PD 7974-6:2004. The application of fire safety engineering principles to fire safety design of buildings- Part 6: Human factors: Life safety strategiesOccupant evacuation, behavior and condition PD 7974-2:2004. The application of fire safety engineering principles to fire safety design of buildings- Part 2: Spread of smoke and toxic gases within and beyond the enclosure of origin Poreh, M and Garrad, G. (2000). A study of wall and corner fire plumes, Fire Safety Journal, 34, 81-98, 2000. Purser, D.A. (2002).Toxicity Assessment of Combustion Products. The SFPE Handbook of Fire Protection Engineering 3rd ed). DiNENNO, P.J (ed.), National Fire Protection Association, Quincy, MA 02269, pp. 2/83 – 2/171. 16 | P a g e UCLAN FIRE www.uclan.ac.uk/fire Tosolini, E, S Grimaz, and E Salzano. "A Sensitivity Analysis of Available Safe Egress Time Correlation." Chemical Engineering Transactions. 31 (2013): 223228. Wood, P.G.(1972).( The behaviour of people in fires. Fire Research Station, UK, Fire Research Note 953. Yuan, L-M and Cox, G. (2001). An Experimental Study of Some Line Fires, Fire Safety Journal, 27, 123, 1. 17 | P a g e
Introduction: In studies related to fire studies there are many consideration about the safety of the people and buildings. In piece of work the calculation and discussion will focus about the required safe escape time (REST). In this case there is a scenario where there 15 members of staff. These member of staff are not member of the public and they are in the MEZZANINE at a warehouse where it is asked to calculate the required safe escape time (REST) of them. In terms of the design of the warehouse there is only one stairs where this is the only way to access to the MEZZANINE and it has two fire exits. In terms of the formula, this is the equation that used to calculate the required safe escape time (REST) t REST =∆t det + ∆t a + (∆t pre + ∆t trav ) . Figure 1 – Ground floor plan of warehouse Figure 2 – Proposed mezzanine arrangement Scenario: The fire will start next the door (see figure 1). The coloured arrows shows the route of the member of the staff to the fire exit to escape. Which is the travel distance. Calculations: RSET is the required calculated time for the occupants of a specific area to escape to safety from the moment of ignition. (British Standards, 2004) A calculation formula is used to calculate REST according to BS7974. 𝑡𝑅𝑆𝐸𝑇 =∆𝑡𝑑𝑒𝑡 + ∆𝑡𝑎 + (∆𝑡𝑝𝑟𝑒 + ∆𝑡𝑡𝑟𝑎𝑣 ) (British Standards, 2004) tRSET = Required Safe Escape Time (s). ∆tdet = Time from Ignition to Detection (s). ∆ta = Time from Detection to a General Alarm (s). ∆tpre = Pre-movement Time for the Enclosure or Building Occupants (s). ∆ttrav = Travel Time of the Enclosure or Building Occupants (s). To get the required safe escape time the data should be collected and searched, while, some cases the engineer has to assume to get the right classification of the problem and how solve it in engineering point of view. ∆𝑡𝑒𝑣𝑎𝑐 = ∆𝑡𝑝𝑟𝑒(1𝑠𝑡 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒+99𝑡ℎ 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒) + ∆𝑡𝑡𝑟𝑎𝑣(𝑤𝑎𝑙𝑘𝑖𝑛𝑔) (British Standards, 2004) In the classification of the standards in terms of the occupancy behaviour it depends on several factors to determine or assume the scenario that might happened when a fire caused and it is classified to several categories. Those categories relays on Occupants alertness, Occupants familiarity, Occupant density, Enclosure/complexity and Examples of occupancy types. According to our scenario and the details given the behavioural scenario will match category A. finally, it is not required to calculate the occupant flow time because there is no queuing. There are two parts to solve the total time of evacuation. First of all, pre-movement time which is also divided to two parts. Therefore, traveling time. (British Standards, 2004) Category Occupants alertness Occupants familiarity Occupant density A Awake Familiar Low Enclosure/complexity Examples of occupancy types One or more Office or industrial Pre-movement time: As it is mentioned the pre-movement time has two parts. The 1st percentile premovement and 90th percentile pre-movement. The 1st percentile pre-movement is the time between or the phase between the starting of the alarm and the movement of the first few occupants when the 90th percentile pre-movement is the time between first few occupant’s movements and the movement the last few occupant’s movement. (British Standards, 2004) According of the scenario of the case the building is not accessed by the public only trained staff can access the building. The criteria of the building is M1, B1 and A1 Management Level M1: the occupants are trained to fire safety management. Building Level B1: a simple rectangular single storey building with a simple layout with clear visual access and exits leading to outside of the building. (British Standards, 2004) Level A1 Alarm System: automatic detection throughout the building, trigging immediate general alarm. (British Standards, 2004) For known these categories, a value for the pre-movement time can be obtained from its table: (British Standards, 2004) ∆𝑡𝑝𝑟𝑒 = 30 + 60 = 90 s Travelling Time: ∆𝑡𝑡𝑟𝑎𝑣(𝑤𝑎𝑙𝑘𝑖𝑛𝑔) = 𝑡𝑟𝑎𝑣𝑒𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑤𝑎𝑙𝑘𝑖𝑛𝑔 𝑠𝑝𝑒𝑒𝑑 ∆ttrav(walking) It is the occupant’s required time to walk into an exit that leads to an escape route . (British Standards, 2004) Assuming that there is no smoke density because the staffs are in industrial building they are familiar with the fire alarm with regards the efficacy of the detection system and the visibility will not be affected. The walking speed is 1.2 m/s. (British Standards, 2004) If it taken by straight line the distance will be 81m but in engineering point of view obstacles, barriers, boxes, etc.… has to be consider that is why the engineer has to assume and add 50% of the straight line distance. 81 𝑡𝑟𝑎𝑣𝑒𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 = 81 + ( ) = 121.5 𝑚 2 ∆𝑡𝑡𝑟𝑎𝑣(𝑤𝑎𝑙𝑘𝑖𝑛𝑔) = 𝑡𝑟𝑎𝑣𝑒𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑤𝑎𝑙𝑘𝑖𝑛𝑔 𝑠𝑝𝑒𝑒𝑑 ∆𝑡𝑡𝑟𝑎𝑣(𝑤𝑎𝑙𝑘𝑖𝑛𝑔) = 121.5 = 101.25 𝑠 1.2 In this case at the far point of the map if there was an occupant the occupant can reach the safe exit at 101.25 seconds. ∆𝑡𝑒𝑣𝑎𝑐 = ∆𝑡𝑝𝑟𝑒(1𝑠𝑡 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒+99𝑡ℎ 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒) + ∆𝑡𝑡𝑟𝑎𝑣(𝑤𝑎𝑙𝑘𝑖𝑛𝑔) ∆𝑡𝑒𝑣𝑎𝑐 90 + 101.25 = 191.25 𝑠 The time needed to evacuate the occupants according the solved equation is 191.25 seconds. Time from Ignition to Detection: To get the calculation of the detection time the minimum fire size has to be assumed for the detection process. Going through some equations to result the heat release rate after that at the end the detection time will be resulted. 𝑄 =∝ (𝑡 − 𝑡𝑖 )2 (British Standards, 2003) 𝑄 = is the total heat release rate from the fire during the growth phase (kW). ∝= is the fire growth parameter (kJ/s3). 𝑡 =is the time from ignition (s) = ∆tdet 𝑡𝑖 = 0, by assumption that there is no time of ignition. First of all, to get the heat release rate the celling jet has to be used. Furthermore, the building which the case consider is classified as an industrial storage building which means it has it has ultra-fast rate about the fire growth rate, so ∝= = 0.188 kJ/s3. (British Standards, 2003) 𝑟 5.3 = = 0.44 > 0.18 ℎ 12 2 𝑇𝑗𝑒𝑡 − 𝑇0 = 5.38𝑄 3 ℎ (CIBSE, 2003) r = is the horizontal distance between the fire axis and the fire detector (m). h = the ceiling height (m). T0 = the ambient temperature = 20 °C Q = is the total heat release rate from the fire (kW). Tjet = is the jet temperature (°C). Tjet = Tdet (detection temperature) = 68 °C, using this equation to get the minimum fire size. Therefore, to get the total heat release rate the equation has to be re-arranged 3 3 (68 − 20)12 2 (𝑇𝑗𝑒𝑡 − 𝑇0 )ℎ 2 𝑄={ } ={ } = 1107𝑘𝑊 5.38 5.38 Moreover, to get the total heat release rate the obtained value of Q has to be used to result the detection time through re-arrangement of the first equation. 𝑄 1107 ∆𝑡𝑑𝑒𝑡 = √ = √ = 77 𝑠 𝛼 0.188 Finally, 77 seconds is the period between the fire ignition and the detection. Final RSET: In the end, putting all the calculated values in the main RSET equation to get the required safe escape time: 𝑡𝑅𝑆𝐸𝑇 =∆𝑡𝑑𝑒𝑡 + ∆𝑡𝑎 + (∆𝑡𝑝𝑟𝑒 + ∆𝑡𝑡𝑟𝑎𝑣 ) 𝑡𝑅𝑆𝐸𝑇 = 76.7 + 0 + (90 + 105) = 271.7 s The required safe escape time for the warehouse is 271.7 seconds.
Scenario When answering Parts A and B above the following information should be used:  The area in question is a storage warehouse for building materials (which may include combustible materials) with dimensions 40m by 32m by 12m high (See Figure 1).  The building will only be accessed by trained staff and not members of the public  The owner of the warehouse wants to add a mezzanine floor (see area in red on Figure 2).  The floor of the mezzanine will be located 8m above the ground floor level.  The mezzanine will be occupied by up to 15 members of staff and there will be no disabled access.  A single open stair will be located towards one end of the mezzanine (see Figure 2) and this will be the only way to access/exit the mezzanine. Part A – 50%  On the basis of the plans and information provided below determine the Required Safe Escape Time (RSET) from the MEZZANINE area following the guidance of BS7974 (i.e. perform the RSET part of an ASET-RSET calculation). 32m 40m 10m Mezzanine Open stair* 15m According to PD 7974-6:2004 Part6 page 7 The formula that determines the escape time for a building is: tRSET = ∆tdet + ∆ta + (∆tpre + ∆ttrav) 8m Where: ∆tdet: it is the time between ignition and detection by an automatic system / first occupant to detect fire cues. ∆ta: it is the time between detection and general alarm operation. ∆tpre: it is the time of Pre-movement for the enclosure or building occupants. ∆ttrav: it is the travel time of the enclosure or building occupants to reach the exist. According to 1.2 page 37 /38 part 6 The time between detection and general alarm operation depends upon the system in the place. However, in this case an automatic detection will be used which can trigger an immediate general alarm therefor, the time in Level 1 will be zero. ∆ttrav (pre-movement) = 𝑡𝑟𝑎𝑣𝑒𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑤𝑎𝑙𝑘𝑖𝑛𝑔 𝑠𝑝𝑒𝑒𝑑 1- Travel distance: figure 1 below shows the location of the fire in order to measure the travel distance. . Figure 1 shows the location of the fire which is on the ground floor. In this situation the fire can change the route of the occupants from door B to door A the reason of that is this the fire covers a big area near to door B. Figure 2 indicate the escape route in case of fire where some of distances are unknown. Length e is the distance of the stair downwards which can be calculated by using Pythagoras theorem. The height of the mezzanine is 8m and the stair is Right-angled. 𝑒 = √82 + 82 = √128 = 11.3𝑚 ≈ 11𝑚 So e = 11m approximately To calculate f which is the distance from the stair to door B which is not straight line same method will be used assuming the position of the door is in the middle. 𝑓 = √82 + 182 = √64 + 324 = 19.6𝑚 ≈ 20𝑚 Finally travel distance = a + b + c + d + e + f = 24 + 4 + 30 + 4 + 11 + 20 = 93 m 2- Walking speed: according to table G.1 page 36 assuming that there is no smoke density and irritancy in addition, the visibility is unaffected by the smoke the walking speed will be 1.2 miles / 1.9 km. ∆ttrav (wallking) = ∆ttrav (flow) = 𝑡𝑟𝑎𝑣𝑒𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑤𝑎𝑙𝑘𝑖𝑛𝑔 𝑠𝑝𝑒𝑒𝑑 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑒𝑜𝑝𝑙𝑒 1.3 ×𝑒𝑥𝑖𝑡 𝑤𝑖𝑑𝑡ℎ = = 93 1.2 = 77.5 𝑠 15 1.3×0.75 = 15.4 𝑠 according to D.3 Page 29 Part 6 door width should be 750 mm for 50 workers or less. This can be suitable width for 15 worker in this case. according to
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