history of the building code - safety codes council · shape factor (no units) stefan-boltzmann...

History of the Building Code

Presented By: Keith Calder

Alberta Safety Codes Council

2018 Conference

May 31th, 2018

Why History?

R.S. Ferguson, NRC, 1959

Model Building Code in Canada

Model Building Code

Model Building Code

CanadaEarly 1900’s

The building codes of the country have not been developed upon scientific data, but rather on compromises; they are not uniform in principle and in many instances Involve an additional cost of construction without assuring more useful or more durable buildings.

William Calder, Senate Select Committee on Reconstruction, 1920

Model Building Code

CanadaEarly 1920’s

Model Building Code

CanadaEarly 1930’s

• Recommendation from 1937:any building code authority in Canada could do no better than adhere to the procedure followed by American authorities and take advantage of their recommendations.

• First Edition of a NBC: 1941

• Substantially based on US Model Codes

• 13 more editions since 1941 NBC

Model Building Code

In the broadest sense, building regulations develop from contingency to contingency. Each one represents an emergency measure taken with very little or no study. As the emergency recedes, the regulation tends to form part of traditional practice. It is added to the pile, which grows and grows.

R.S. Ferguson, NRC, 1974

Occupant Load Factors

Example: Office Occupant Load Factor

• 1850’s: Crimean War

• Large loss of life in barracks and hospitals

Example: Office Occupant Load Factor

• 1860’s: Florence Nightingale proposed minimum volumetric space per person

• Ventilation requirements a function of:

• Room dimensions,

• External and internal temperatures,

• Number of occupants in the room,

• Time the room is occupied, and

• Use of the room.

Example: Office Occupant Load Factor

• 1870’s: Max von Pettenkofer

• developed cubic limits for various occupancies as a function of exhaled carbonic acid

Example: Office Occupant Load Factor

Business Building

100

ft2

Maximum

Desirable

Example: Office Occupant Load Factor

• 1908: Elevator design – R.P. Bolton

• Required an understanding of maximum occupant load

• Bolton - office occupancies:

• Existing ventilation requirements as basis for calculation

• Confirmed calculation through statistical analyses of highest density offices in the City of New York

Example: Office Occupant Load Factor

Example: Office Occupant Load Factor

Example: Office Occupant Load Factor

• 1911: Shirtwaist Factory Fire, New York City

Example: Office Occupant Load Factor

Example: Office Occupant Load Factor

• Regulate occupant numbers based on number and size of exits

• Was found to be too complicated

Example: Office Occupant Load Factor

• 1924: developed an occupant load formula to replace tables to simplify egress analysis.

• Based on several building characteristics

• Was found to be too complicated

Example: Office Occupant Load Factor

• 1927 Building Exits Code (NFPA 101)

Example: Office Occupant Load Factor

• 1935: “The Design and Construction of Building Exits”

• 1941 NBC:

Example: Office Occupant Load Factor

• 1975 NBC:

• 2015 NBC:

9.30 m2/Person (100 ft2/Person)

• Recent statistical studies in US*:

150 to 200 ft2/Person

*Does not include call centers

Spatial Separation

• 2014 ABC, Sentence 3.2.3.1.(1)

Spatial Separation Requirements

Great Fire of Rome in 64 AD

Great Fire of London in 1666

• Great Fire of Chicago – October 10, 1871

• Great Fire of Boston – November 9, 1872

Great Fire of Chicago and Boston

Great Fire of Vancouver 1886

Calgary Fire - 1886

The recently organized Calgary Fire Department successfully used the recently ordered but not yet paid for chemical engine.

1886: Fire began at the rear wall of the local flour and feed store, and spread through the community's wooden structures

To reduce the potential for future fires, city officials drafted a law that all large downtown buildings were to be built with Paskapoosandstone

“Invisible Heat”: 1913 NFPA Quarterly

Fire Limits

• Early History of Development of Requirements• Limits Calgary 1913:

• These requirements were challenging to enforce, maintain, restrictive and city-specific

• Needed a better “building independent” system

Fire Limits

1941 NBC

• National Building Studies, London, 1950

• Spread of fire from one building to another can occur through one or a combination of the following factors:• Flying brands• Convection• Radiation

• Flying brands and convection addressed through protective construction

• Radiation significant for larger fires (i.e., full building involvement)

New Approach – Physics Based

• Calculated based on fundamental heat transfer:

Radiant Heat

ሶ𝑞" = 𝜙 ∙ 𝐸

𝐸 = 𝜎 ∙ 𝑒 ∙ 𝑇4Emissive Energy (kW/m2)

𝜙 =2

𝜋

𝐴𝑆

𝐴𝑆 + 4

𝑎𝑟𝑐𝑡𝑎𝑛𝐴 ∙ 𝑆

𝐴𝑆 + 4

+𝐴 ∙ 𝑆

𝐴 ∙ 𝑆 + 4𝑎𝑟𝑐𝑡𝑎𝑛

𝐴𝑆

𝐴 ∙ 𝑆 + 4

Shape Factor (No Units)

Stefan-Boltzmann Constant

(5.67E-11 kW/m2 K4)

Emissivity (No Units) Absolute

Temperature (K)

Heat Flux (kW/m2)

• Illustration of Radiant Heat Transfer

Radiant Heat

Emissive Power

Incident Heat Flux ሶ𝑞"

• Limit the potential for ignition of neighbouring buildings by radiant heat flux• A function of ignition properties of common

combustible building materials (1950’s)• Combustible exterior cladding/wall materials were

primarily cellulosic (wood)• Slight flow of resin on timber: 100 °C• Considerable flow of resin on timber: 150 °C• Severe charring on surface of timber (no flaming): 200 °C• 150 °C considered the maximum temperature to which

timber could safely be heated without risk of easy ignition and rapid spread

New Approach - Performance

1953 NBCC

1953 NBCC

1953 NBCC

1953 NBCC

• St. Lawrence Burn Tests:• Six 2-storey dwellings of

similar size and layout and two larger structures (school and community hall)

• One dwelling test eliminated due to problems

• Current table values primarily based on results from Test Nos. 4 and 5

• Fire Service response based on Test No. 5

St. Lawrence Burns - 1958

Burn Setup

Ignition

Notification of Test Start

Burn No. 5

Burn No. 5 Observations

(482 ºC)Flashover ~ 600 ºC

Additional fuel source

Flame Front

Burn Results

Conversion into Regulations - Source

• Radiation Source (Windows)• Actual: Significant flame extension out windows

• Regulation: Window area theorized as the only source of radiant heat for purposes of simplification

Conversion into Regulations - Source

Actual Regulation

3.15 X Opening Area for Low Hazard

6.30 X Opening Area for High Hazard

• Flame Front• Actual: Varied 2 to 7 ft within first 10 minutes

• Regulation: For simplification – 6 ft (~1.8 m)

Conversion into Regulations – Flame Front

Burn No. 5, Flame Front @ ~16

minutes – approx. 15 feet

Conversion into Regulations – Peak Heat

8.5

8.5 cal/cm2·s

= 356 kW/m2

29 to 40 cal/cm2·s (1214 to 1675 kW/m2)

• Regulation:• Building separations

associated with peak heat not practical.

• Assume fire department intervention when peak heat reaches approx. ¼ highest values measured.

• Heat at 10 to 11 minutes for Burn No. 5

• Approx. 356 kW/m2

• Calculated based on fundamental heat transfer:

• Acceptable heat flux at a target (Target Criteria): • Ignition of wood with piloted ( ) source: 12.5 kW/m2

• Autoignition of wood ~ 30 kW/m2

• Need to relate heat flux to openings

Radiant Heat

ሶ𝑞" = 𝜙 ∙ 𝐸Heat Flux (kW/m2)

𝜙 =ሶ𝑞"

𝐸Openings

Peak Heat

Target Criteria

Conversion into Regulations – Target Criteria

• Target criteria expressed as a ratio of target heat flux and peak heat:• High hazard (combustible lining) - Table 3.2.3.1.C

• Low hazard (noncombustible lining) - Table 3.2.3.1.B

𝜙𝑐 =ሶ𝑞"

𝐸=12.5 𝑘𝑊/𝑚2

356 𝑘𝑊/𝑚2= 0.035

𝜙𝑐 =ሶ𝑞"

𝐸=

12.5 𝑘𝑊/𝑚2

12 × 356 𝑘𝑊/𝑚2

= 0.07

• Equation (unsprinklered):

Table Equation - Unsprinklered

% 𝑜𝑝𝑒𝑛𝑖𝑛𝑔𝑠 = 100𝜙𝑐𝜙

𝜙𝑐 = 0.07 𝐴, 𝐶, 𝐷, 𝐹3 𝑜𝑟 0.035 (𝐸, 𝐹1, 𝐹2)

𝜙 =2

𝜋

𝐴𝑆

𝐴𝑆 + 4

𝑎𝑟𝑐𝑡𝑎𝑛𝐴 ∙ 𝑆

𝐴𝑆 + 4

+𝐴 ∙ 𝑆

𝐴 ∙ 𝑆 + 4𝑎𝑟𝑐𝑡𝑎𝑛

𝐴𝑆

𝐴 ∙ 𝑆 + 4

𝐴 =ℎ 𝑤

𝑑2

𝑑 = 2 ∙ 𝐿𝐷 − 1.8288 (6 𝑓𝑡. )

𝑆 =ℎ

𝑤𝑜𝑟

𝑤

ℎ, 𝑤ℎ𝑖𝑐ℎ𝑒𝑣𝑒𝑟 𝑖𝑠 𝑔𝑟𝑒𝑎𝑡𝑒𝑟

• Equation (sprinklered):

Table Equation - Sprinklered

% 𝑜𝑝𝑒𝑛𝑖𝑛𝑔𝑠 = 100𝜙𝑐𝜙

𝜙𝑐 = 0.14 𝐴, 𝐵, 𝐶, 𝐷, 𝐹3 𝑜𝑟 0.07 (𝐸, 𝐹1, 𝐹2)

𝜙 =2

𝜋

𝐴3

𝐴3 + 4

𝑎𝑟𝑐𝑡𝑎𝑛𝐴 ∙ 3

𝐴3 + 4

+𝐴 ∙ 3

𝐴 ∙ 3 + 4𝑎𝑟𝑐𝑡𝑎𝑛

𝐴3

𝐴 ∙ 3 + 4

𝐴 =ℎ 𝑤

𝑑2

𝑑 = 2 ∙ 𝐿𝐷 − 1.8288 (6 𝑓𝑡. )

• Burn 5: Wind was 10 to 14 mph (16 to 22.5 kph), NRC:• “The most important item was wind speed and

direction, because of its effect in projecting the flame front some distance from the window openings of the burning building.”

• “Radiation levels were affected by wind conditions, but the results obtained were not adequate to allow a quantitative analysis of the effects.”

• Burn No. 5 transitioned to flashover within 2.5 to 3 minutes

• Fuel load in Burn 4/5 is consistent with surveys of homes today – proportion is different

Key Takeaways

Exterior Wall Construction

< 10%

< 25%

< 50%

< 100%

10%

25%

50%

100%

1.2 m

Noncombustible

Combustible or Noncombustible

Flame Front (Convection) Zone

No Foamed Plastic

Insulation

Groups A, C, D, and F, Division 3

Challenges - Interpolation

• As a simplification, NBCC approach assumes “grey radiator” exposing building face:

• The “grey radiator” assumption is reasonable and approaches actual physics at increasing separation distances

Challenges – Grey Radiator and Window Clustering

=

• “Grey radiator” assumption breaks down where unprotected openings are clustered and at short separation distances

• Regulated in the 2010 NBCC:

Challenges – Window Clustering

Challenges – Window Clustering

Wall Area = 150 m2

Opening Area = 10.9 m2

Percent Opening = 7.3%

Ratio = 1.5

1.65 m

1.65 m

15 m

10 m

0.5 m

LD = 1.6 m

• 2015 NBC:

Challenges – Fire Department Response

• 10 minute response time expectation based solely on results from Burn No. 5

• The radiant heat intensity for Burn No. 4 reached ¼ Burn No. 5 at approx. 10-11 minutes.

• NRC (1959) - “Spatial Separation of Buildings”:

Challenges – Fire Department Response

• NRC (1961) - “Study of Performance Standards for Space and Site Planning in Residential Development”:

• NRC (1982) – Letter to “Codes and Standards” from M. Galbreath:

Challenges – Fire Department Response

• 1970 NBC:

• 1975 NBC:

Challenges – Fire Department Response

Spatial Separation – Current Issues

Spatial Separation – Current Issues

QUESTIONS?

ContactKeith Calder

+1 604-295-3422

kcalder@jensenhughes.com

For More Information Visit

www.jensenhughes.com