Establishing the Risk Basis of Building Size Limits

Transcription

1 Establishing the Risk Basis of Building Size Limits A look at the history of development of our building codes and safety opportunities to facilitate wood design initiatives. Presented on January 27, 2015 by Keith Calder, Sereca Consulting Inc. Disclaimer: This presentation was developed by a third party and is not funded by WoodWorks or the Softwood Lumber Board.

2 The Wood Products Council is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider #G516. Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-aia members are available upon request. This course is registered with AIA CESfor continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner ofhandling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

3 Course Description Over the last 80 years, prescriptive height and area limitations have remained relatively unchanged in North American building codes while technological advances and fire service capabilities have improved considerably. Through an examination of historical code development and identification of the risk factors on which codes are based, we can set the stage for a re-examination of public perception with regard to combustible construction. This presentation will cover techniques for mitigating fire damage and reducing fire spread while describing how an understanding of code intent can be used to argue equivalent fire performance when wood solutions lie outside typical code-approved applications.

4 Learning Objectives Evaluate the evolution of fire life safety codes, including the impact of historical fire events on current requirements. Review the building size limitations in current codes and the original risk factors on which they were based. t. Explore techniques for mitigating fire damage and methods for reducing fire spread. Demonstrate, with an understanding of code intent, how equivalent fire performance can be achieved through the alternate means and methods procedure.

5 General Approach The International Building Code (IBC) limits the use of wood in larger and taller buildings relative to other materials based on its combustibility How can the limitations to the use of wood be addressed? Development of alternative solutions to the IBC requirements (equivalents), or Changes to the IBC requirements How is this achieved? Identification of the risk basis of the limits Re-examination of the risk basis in a current context Development of means to address the risk

6 The Challenge

7 Building Code Regulations The pace of innovation in the built environment is increasing and innovation results in change The adaptability of a building code to change is a function of its regulatory structure The IBC is a compilation of primarily specification-based regulations supplemented by a few performance-based regulations

8 Regulation Types Specification-based regulations tell you what to do: Performance-based regulations tell you what you need to achieve:

9 Specifications Building Size Limits Building size limits are expressed in specification format:

10 Specifications - Development Incidents of significant scale or impact occur and draw attention to building design issues Investigation and analysis follow to establish the conditions that led to the incident Solutions are developed to limit future incidents and are based on contemporaneous knowledge, capability, materials and methods The solutions are written in specification format, becoming frozen in time San Francisco Conflagration

11 Specifications - Challenges Over time, maintaining the link between a specification and the factors considered in its development (reason) becomes increasingly challenging, limiting future changes and alternative solutions R.S. Ferguson, NRC, 1959 This is the case for the height and area limits and a proposed approach to a solution follows

12 Approach to a Solution Implicit Risk: What is/was the risk that initiated the development of the specification(s)? Mitigating Measures: What capability, materials and methods were considered in mitigating the risk? Acceptable Risk: To what level is/was the risk mitigated? Current Context: Are the specifications still relevant? Re-examination of implicit risk, mitigating measures and acceptable risk.

13 Implicit Risk, Mitigation Measures and Acceptable Risk

14 Great Fire of Rome in 64 AD

15 Great Fires of London in 1135 and 1212

16 Summary Early Times Conflagrations in 1087 and 1135 resulting in destruction of most of the City of London Majority of buildings at that time were constructed of wood, roofed with straw. High building density Implicit Risk: Mitigation: Fire spread from building to building resulting in conflagration. Stone wall between houses: 3 feet thick (party wall/firewall) Acceptable Risk: Limit fire spread to individual buildings (primarily houses)

17 Summary London 1666 to 1774 Implicit Risk Considerations Implicit Risk: Mitigation: Fire spread from building to building resulting in conflagration. Brick or stone wall between houses: 13 inches thick and 18 inches above the roof (party wall/firewall) Brick or stone exterior walls Intended Result: Limit fire spread to individual buildings (primarily houses)

18 London 1850 s 60 ft 60 ft 60 ft

19 London 1873

20 Summary London: 1774 to 1873 Implicit Risk Considerations Implicit Risk: Mitigation: Single buildings (warehouses) increasing in size resulting in fire size beyond the capability of the responding fire department. Increased potential for conflagration. Containmentby limitingheight/volume assuming fire service intervention Height of 60 to 65 ft and cubic capacity of 216,000 cubic feet. Intended Result: Limit fire spread to individual buildings.

21 USA 1872 to 1930 s Great Fire of Chicago October 10, 1871 Great Fire of Boston November 9, 1872 These fires called attention to the substandard conditions of construction in cities across the United States

22 USA 1870 s Standard Building Standard Building and associated limits based on insurance rating system: Defined building characteristics upon which insurance rates could be set Deviations from the standard resulted in higher rates Improvement of the standard resulted in discounted rates Variations to the Standard Building features were later quantified in greater detail

23 USA 1873 Standard Building New York Board of Fire Underwriters January 1873: Standard Building height and area limits Note that the volumetric limit based on an area of 5,000 ft 2 and height of 60 feet is 300,000 ft 3. This was the limit for existing warehouses in the City of London

24 USA 1872 to 1930 s Fire Service Capability Rationale for limits:

25 USA 1872 to 1930 s Insurance Rating System Insurance rating system modifiers: Feature Occupancy: Modifiers A function of hazard level (experiential) Type of Construction: Fireproof and non-fireproof Accessibility: Sprinklering: Area: Height: Number of building sides facing a street Gradual recognition of benefit with increased reliability Incremental increases/decreases as a function of area Incremental increases to a threshold level of 7 storeys then significant increases

26 USA 1890 to 1930 s Model Building Code Insurance rating schedule translated into regulation Published by the National Board of Fire Underwriters in 1905 Base area: 5,000 ft 2 Area modifiers: Occupancy Height Type of construction Streets Facing Sprinklers

27 USA 1872 to 1930 s Sprinkler Factor Sprinkler modifier example (140 year history): 1874: first successful commercial automatic sprinkler was patented by Henry Parmelee s: 7.5% to 10% reduction of insurance rates 1890 s: 20% reduction in insurance rates 1896: First edition of NFPA 13 increased reliability, 30% to 33⅓% reduction in insurance rates 1905: 50% reduction in rates for standard systems and 66⅔% reduclon in rates for supervised systems. 1905: Credit of 50% to 66⅔% for sprinklers translated into Code context in 1905 NBFU Model Code by allowing an increase in area of 50% to 66⅔% where sprinklers are provided

28 USA 1872 to 1930 s Sprinkler Factor 1915: 100% increase permitted for Mill construction 1921: NFPA Proceedings 2012: IBC, 200% increase of table values permitted for multi-storey buildings

29 Summary USA 1872 to 1930 s Implicit Risk Considerations Implicit Risk: Fire size beyond the capability of the responding fire department Mitigation: Significant property loss Increased potential for conflagration Height of 5 to 6 storeys (50 to 60 ft) and base area of 5,000 square feet Increases in height and area based on type of construction, occupancy, streets facing and sprinklering Intended Result: Limit fire spread to individual buildings.

30 USA 1930 s to Current Limits included in the three model codes: 1927 Uniform Building Code (UBC) 1946/1947 Southern Standard Building Code (SSBC) 1950 Basic Building Code (BBC) These limits were revised and evolved up to IBC Occupancy Committee Maximum height and area of each of the three model codes was adopted for use in the IBC Some modifications as a result of differences in format

31 Summary USA 1930 s to Current Implicit Risk Considerations Implicit Risk: Inadequate evacuation Full building involvement Fire size beyond the capability of the responding fire department Collapse of high buildings Mitigation: Intended Result: Increased potential for conflagration Height of 6 storeys (50 to 60 ft) and area limits as a function of occupancy, type of construction, fire-resistance, streets facing and sprinklering. Increases in height and area based on type of construction, occupancy, streets facing and sprinklering Combustible buildings: Limit fire spread to building Noncombustible buildings (no rating): Limit fire spread to building Noncombustible buildings: Limit fire spread to storey

32 Implicit Risk, Mitigation Measures and Acceptable Risk: Area Summary Total anticipated fire size within the capability of a responding fire service Limit area to basis areas of: 5,000 square feet for combustible construction 10,000 square feet for non-combustible construction Variations as a function of relative risk (occupancy, streets facing, sprinklers)

33 Implicit Risk, Mitigation Measures and Acceptable Risk: Height Summary The basic height limit for combustible construction: has remained relatively consistent of the previous approximately 160 years at 5 to 6 storeys of 50 to 60 feet (15 to 18 m) has had some variation in concept recognizing containment of fire to a single storey Combustible construction/unprotected noncombustible: building height limited assuming the potential for whole building involvement and fire fighting from exterior Noncombustible construction: assumes fire fighting from interior and burn-out where firefighting is ineffective. Intent is to contain fire to a single storey

34 Current Context

35 Current (Evidentiary Risk): Statistical Analysis Current fire loss statistics collected in a manner that does not correlate with building code principles Growth and spread of fire can be characterized as a function of fire type Compartment Concealed space Exterior Data collected within a fire type framework to gauge effectiveness of Codes Published: Interflam 2013, London

36 Evidentiary Risk Compartment Fires 56 fires 90% of the fires originating in fire rated compartments were contained to the compartment of origin (primarily unsprinklered) Remaining 10% spread beyond the fire rated compartment to adjacent compartments or the exterior of the building Building size and construction type were not significant factors

37 Evidentiary Risk Concealed Space Fires 16 fires 44% of fires originating in concealed spaces were contained to the space of origin Remaining 56% spread to adjacent concealed spaces or compartments Significant spread occurred once the fire reached the attic space

38 Evidentiary Risk Exterior Fires 28 fires 8% of exterior fires were limited to a single storey of exterior damage. The remaining 92% of fires spread to involve more than 1 storey In many cases resulted in significant damage to the entire roof of the building Magnitude of damage to sprinklered and unsprinkleredbuildings similar as a result of sprinkler limitations associated with NFPA 13R

39 Statistical Summary Course of Construction Compartment Concealed Exterior Number of Fires % 43% 5 0 Increasing Damage

40 Current Context: Fire-Rated Compartments Fire-rated compartments: Unsprinklered: perform as intended by the Codes, limiting the growth and spread of fire to the compartment of origin regardless of building size or height. Sprinklered: rarely result in fire spread. National Research Council Canada relative to 3-4 storey increase for Group C Occupancies: Canada - Standing Committee on Fire Protection 1990 s:

41 Considerations Current Context Existing limits set long ago when understanding of fire engineering was limited Since then: Firefighting techniques, equipment, response and overall capability has advanced significantly Construction methods and materials have advanced Analysis techniques have evolved significantly Sprinkler effectiveness has increased Studies have shown that fires tend to be contained to fire compartment of origin (sprinklered and unsprinklered)

42 Future Considerations

43 Future Considerations - Capability Re-examine fire service capability relative to building size Fire engine design Jacques Besson, 1570

44 Future Considerations - Capability Re-examine fire service capability relative to building size Equitable building fire, New York, 1912

45 Future Considerations - Capability Re-examine fire service capability relative to building size Los Angeles, February 05, 2007

46 Future Considerations - Materials Consider limits based on material-independent fire performance Original assumption: Material contribution to fire considered significant - conflagrations What is the actual risk associated with material contribution? Limited research Forensic experience suggests material contribution to fire not significant More research required

47 Future Considerations Analyses Techniques Analysis techniques have advanced significantly in the last several decades and Better able to analyze and predict: Material behavior to fire Fire growth and spread Occupant response and movement Probabilities and consequences

48 Future Considerations Methods Original limits were established at a time when building compartmentation was minimal: Open stairs, Unprotected elevators/shafts Risk of fire spread to involve entire building was greater than it is today (statistics) Consider the fire compartment as the unit of control The trend is toward the choice of smaller spaces for regulation purposes [and] as the space basis for regulation is reduced, a better fit between control and hazard is achieved. R.S. Ferguson, National Research Council of Canada, 1970 s Fire compartmentation has increased over time

49 Future Considerations Methods Continued Fire-rated compartments: Unsprinklered: perform as intended by the Codes, limiting the growth and spread of fire to the compartment of origin regardless of building size or height. Sprinklered: rarely result in fire spread. National Research Council Canada relative to 3-4 storey increase for Group C Occupancies: Canada - Standing Committee on Fire Protection 1990 s:

50 Future Considerations Methods Continued Limit fire compartment areas rather than building height and area: NFPA 5000, Appendix D, Enhanced Fire Compartments New Zealand approach

51 QUESTIONS? This concludes The American Institute of Architects Continuing Education Systems Course Keith Calder Sereca Fire