UNIT 9: CONCEPTS OF EGRESS AND EGRESS CALCULATIONS AND MODELING

1. UNIT 9:CONCEPTS OF EGRESS AND EGRESS CALCULATIONS AND MODELING

2. TERMINAL OBJECTIVE • Given a sample scenario, explain the related concepts of egress and be able to evaluate egress calculations and modeling to determine if the model produces egress performance results that maintain conditions tenable for human life.

3. ENABLING OBJECTIVES The student will: • Describe basic fire-related human behavior in the built environment. • Explain how the use of occupancy classification affects overall fire and life safety protection features. • Compare four strategies for preserving life in structures during fires or other environmental emergencies.

4. PEOPLE MOVEMENT • Evacuation • Full or partial • Defend in place • Area of refuge • Area of rescue assistance • Phased relocation

5. SUCCESSFUL EVACUATION • Involves people movement through detection, notification, and instruction • Provides means of movement through exit capacity, exit accessibility, and exit discharge • Protects egress path against products of combustion

6. TO DEFEND IN PLACE • Restrict movement of occupants • Defend the area by protecting against the products of combustion and preserving structural integrity

7. FUNDAMENTAL CONSIDERATIONS • Time • Occupant characteristics • Nature of threat • Fire • Earthquake • Gas leak • Physical attack

8. TIME • Ignition • Detection or awareness • Hazard threshold

9. TIME (con.)

10. OCCUPANT CHARACTERISTICS • Age • Mobility • Awareness • Knowledge • Density • Discipline

11. NATURE OF THE THREAT • Ignition potential • Fire growth rate • Spread of smoke and fire • Egress compromise

12. LIFE SAFETY FUNDAMENTALS • Remain the same for all occupancies

13. FUNDAMENTAL PRINCIPLES • Adequate exits without dependence on any single safeguard • Structural integrity while exiting • Exits based on nature of occupancy • Exits are clear, unobstructed, and unlocked • Exits and routes are clearly marked

14. FUNDAMENTAL PRINCIPLES (con.) • Adequate lighting of egress system • Early warning • Redundant exit arrangement • Enclosure of vertical openings • Special needs of occupancy

15. TOTAL PROTECTION CONCEPT • Prevent ignition • Fire detection • Control of fire development • Confine fire effects • Fire extinguishment • Refuge or evacuation • Occupant/Staff training

16. EGRESS-RELATED HUMAN FACTORS • Physical characteristics of human body • Individuals tend to establish “territories” • Most adult males measure 21 inches at shoulder • Side sway of approximately 1.5 inches

17. TRAVEL SPEED • Based on actual observation in various studies • 250 to 275 ft./min. level • 187 ft./min. on stairs • 196 ft./min. level for disabled • 75 ft./min. stairs for disabled

18. RESEARCH FINDINGS • 1981 presentation by J.L. Pauls at International Life Safety and Egress Seminar • Rules developed 20 years before research • Two approaches to people movement: • Carrying capacity • Human response/Hydraulic model

19. CARRYING CAPACITY • Assumes occupants will react immediately • Evacuate in orderly fashion • Actually occupants ignore or downplay initial cues

20. HYDRAULIC MODEL • Occupants are alert, able bodied, and ambulatory. • This approach depends on the “safe end” of the evacuation system. • Two phases--time to start and movement. • Model only accounts for movement.

21. PANIC: GENERAL ASSUMPTIONS From Guylene Proulx in Society of Fire Protection Engineers (SFPE) Handbook: • Panic is rare even in fire • Individual behavior tends to be altruistic and reasonable • Initially ignore cues • Will exit as they entered

22. ASSUMPTIONS • Evacuation is a social response--tend to act as group • Common problems include faulty communication, circulation hazards, and “way-finding” problems • Influence of directives and instructions

23. INSTRUCTION INFLUENCES

24. MODEL-BASED EGRESS TIME CALCULATIONS • Required Safe Egress Time (RSET) • Available Safe Egress Time (ASET)

25. REQUIRED SAFE EGRESSTIME FORMULA

26. EXIT CAPACITY • “Unit of exit width”: 22 inches • Minimum necessary for orderly, single file movement of persons along passageway • Accommodate shoulders of an adult male • Based on 1935 National Bureau of Standards (now NIST) Design and Construction of Building Exits • Confirmed by London Transit Board in 1958

27. MINIMUM WIDTHS ESTABLISHED • “Smooth” movement of people • Doorways minimum 36 inches with 32-inch clear opening • Pre-1970s • -- 32-inch door with 28-inch clear opening • Stairways minimum of 44 inches

28. UNIT OF EXIT WIDTH • Accommodate designated number of people • Assumed to be reasonably alert, healthy individuals • Capacity per unit dependent upon level travel or stairs • Level travel 100 persons per unit • Stair travel 60 persons per unit

29. METHODOLOGY CHANGES • Occurred in approximately 1988 • Unit of exit width replaced by smaller increments of egress width and capacity • Approach contained in current codes and legacy codes • Based on previously used values for full units • Small increments added to capacity

30. VALIDITY OF APPROACH • Canadian research in tall buildings and larger assembly occupancies

31. DOCUMENTED RESEARCH • Crowds do not move in regular files or lanes. • Side-to-side sway prevents individuals from walking shoulder-to-shoulder.

32. CAPACITY FACTORS • Level travel for most occupancies • 0.2 inches per person • Stairway travel for most occupancies • 0.3 inches per person • Some occupancies have special factors • Hazardous and institutional • Allowance for automatic sprinklers

33. EXIT CAPACITY • Capacity is based upon the occupant load. • Exit capacity is calculated using the clear width. • Clear opening based on door at 90 degrees. • Actual clear opening can be measured and used in an existing building.

34. STAIR HAZARDS • Approximately 2,500 people die annually from falls on stairs/steps • Over 1 million treated in emergency rooms due to falls on stairs/steps

35. STAIR RESEARCH • 1935 NBS Design and Construction of Stairs • Most common was 7- to 7-1/2 inch risers and 10- to 10-1/2 inch treads • Meet commonly accepted “rules” of the time

36. ANTIQUATED “RULES” • Sum of riser and tread not less than 17-1/2 nor more than 18 inches • Sum of two risers and one tread not less than 24, nor more than 25 inches • Product of riser and tread fall between 70 and 75

37. 1935 NBS RECOMMENDATIONS • Sum of height of two risers and one tread (in inches) equal not less than 24, nor more than 25 • Maximum riser height of 7-3/4 inches • Treads not less than 9 inches • Uniform width and risers in any one flight

38. RULE’S ORIGIN • François Blondel--Royal Academy of Architecture in Paris in 1672 • Concluded that normal walking pace (24 inches) must be decreased by a regular and fixed amount to allow the foot to be raised in the climbing of stairs

39. “THE DIMENSIONS OF STAIRS” • Published in Scientific American in 1974 • Found that rule could produce stairways with extremely narrow or wide treads • Average human being now larger than in the 17th century • Today’s inch is shorter than the unit employed by Blondel

40. NEW RECOMMENDATIONS • Risers between 4 and 7 inches • Treads between 11 and 14 inches • Also confirmed with NFA study An Analysis of Behavior of Stair Users

41. STAIRWAYS • Minimum clear width: 44 inches • Maximum riser height : 7 inches • Minimum riser height : 4 inches • Minimum tread depth: 11 inches

42. ADDITIONAL ISSUES • No more than 3/16-inch variance between adjacent risers or treads • Tolerance between largest and smallest riser in any flight not more than 3/8-inch • Allowances for bottom riser adjoining a sloping grade

43. LANDINGS • Not less than width of stair, measured in direction of travel • Do not have to exceed 48 inches

44. HEADROOM • 6 feet 8 inches minimum • Measured from nosing of stair

45. PathFinder • Software is an agent based egress and human behavior simulator • Provides graphical user interface for simulation design and execution • 2D and 3D visualization tools for results analysis

46. PathFinder Video Presentation

47. ACTIVITYUSE OF PATHFINDER MODEL • Using the PathFinder Example Guide • Complete the examples in Chapter 2 and 3 • This is an individual activity

48. ACTIVITYEVALUATION OF ATRIUM EGRESS • Import the PyroSim file from Unit 6 • Follow the Pathfinder instructions in the Examples Guide Chapter 6 • Assume the atrium is a business occupancy for occupant load purposes • Assume the it is requested to use the atrium as an assembly occupancy

49. SUMMARY