Example IBC Code Analysis for Fire Safety

IBC Code Analysis for Fire Safety

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Example

Example Problem: Check the proposed structure for compliance with the IBC 2015 code on: 1. Height and number of stories; and area per story 2. Number of exits; egress width of doors, corridors and stairs; and egress travel distance for each room and story

Structure: UA Retail Center on Bryant Drive. See full set of drawings in class UA-Box folder.

1. Check proposed building height, number of stories and plan area per story.

The IBC limits the size of the building to provide an acceptable level of risk in the event of a fire. Building height and area limits are a function of the use of the building (occupancy classification) and the type of construction.

1.1 Occupancy Classification

The room numbers, room descriptions and room areas from the building program are listed below for each story. The occupancy classification for each room is determined using IBC 2015 Section XXX.

Level 1:

Room Number

Room

Area, sf

Occupancy Classification

1001 SALES AREA

7464

M

1001A FITTING HC

48

M

1001B FITTING

36

M

1002 SPRINK. RISER

23

S-2

1003 ELEC

53

S-2

1005 STOCKROOM

742

S-2

1006 OFFICE

130

B

1006A CL

46

S-2

1011 JAN

58

S-2

1012 STARBUCKS (not enclosed)

1013 STARBUCKS ENGINE

449

A-2

1014 STARBUCKS KITCHEN

97

A-2

1015 STORAGE CORRIDOR

314

S-2

LEVEL 1 TOTAL

9,460

Level 2:

Summary for Level 1:

Occ. Class.

Area, sf

A-2

546

B

130

M

7548

S-2

1236

Summary for Level 2:

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Example

Room Number

Room

Area, Occupancy sf Classification

Occ. Area, Class. sf

2000 SALES AREA

5859

M

2001 BREAK ROOM

181

A-2

2002 JAN.

29

S-2

2005 TELE/DATA

105

S-2

2006 ATTIC STOCK

157

S-2

2007 EL. EQUIP.

83

S-2

2008 MANAGER'S OFFICE

140

B

2009 STOCK ROOM

1422

S-2

2012 STARBUCKS STORAGE 1040

S-2

2013 OFFICE

88

B

2014 STARBUCKS SEATING

735

A-2

LEVEL 2 TOTAL

9,839

A-2

916

B

228

M

5859

S-2 2836

9,839

The main occupancy of Level 1 is M (Mercantile). Since the floor area of the S-2 occupancy exceeds 10% of the floor area of the story, this occupancy cannot be considered an accessory occupancy. (IBC Section 508.2.3). Therefore, Level 1 is classified as mixed-use.

By the same reasoning, Level 2 is classified as mixed-use.

Since no occupancies are H-2, H-3, H-4, H-5, I-1, R-1, R-2 or R-3, no separation is required (IBC Section 508.3.3).

Occupancy Classification = Mixed Use, Non-Separated

1.2 Type of Construction

Assume the building elements will be unprotected non-combustible materials. The fire-resistance ratings for these

elements are therefore 0 hrs (Table 601).

Type Construction = IIB

Assume also that the building will be have fire sprinklers throughout

Sprinklered

1.3 Allowable Building Height For mixed, non-separated occupancies, the allowable building area and height of the building or portion thereof shall be based on the most restrictive allowances for the occupancy groups under consideration for the type of construction of the building in accordance with Section 503.1 (IBC 2015 Section 508.3.2).

Therefore determine the allowable height and allowable number of stories for each occupancy; use the most restrictive to determine the allowable height and number of stories for the building.

Allowable building height from IBC 2015 Table 504.3 and allowable number of stories from IBC 2015 Table 504.4, for buildings equipped throughout with an automatic sprinkler system.

Occ. Type

A-2 B M S-2 min

Allowable

Height, ft 75 75 75 75

75

Stories

Stories Allowed 3 4 3 4

3

IBC Code Analysis for Fire Safety

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Example

Most restrictive occupancy is Occupancy Category A or M. Therefore allowable height = 75 ft, allowable number of stories = 3.

Actual building height = 37.5 ft < 75 ft = Allowable Ht, OK Actual number of stories = 2 < 3 = Allow No. Stories, OK 1.4 Allowable Building Area Use a similar procedure to determine the allowable area per level as used in the section above; i.e. calculate the allowable area for each of the occupancy categories and use the most restrictive for the entire level.

The maximum allowable building area per story is calculated based on occupancy classification, single-story or multi- story, and whether the building is sprinklered. The allowable area can be increased based on the amount of building frontage on public way or open space (2015 IBC Section 506.3.3).

Frontage Increase Factor, If for mixed-occupancy multistory buildings (Eqn. 5-5):

If

[

F P

0.25 ]

W 30

F = building perimeter that fronts a public way or open space with a width of at least 20 ft

P = building perimeter

W = width of public way or open space (max. W = 30 ft)

If

[

600 600

ft ft

0.25]

30 30

ft ft

0.75

Allowable area, Aa , for mixed-occupancy, multistory buildings (IBC 2015 506.2.4:

Aa [ At (NS I f )] Eqn 5-3

At = tabular area factor (NS, S13R or SM value, as applicable) NS = tabular allowable area factor for a non-sprinklered building

For Occ. Type A-2:

Af [ 28,500sf (9,500sf 0.75] 35,625sf

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Example

The most restrictive occupancy category is Occupancy Category A. Therefore, the allowable area for each level is 35,625 sf.

Level 1 Actual Area = 9,460 sf < Allowable Area = 35,625 sf, OK Level 2 Actual Area = 9,839 sf < Allowable Area = 35,625 sf, OK

2. Design egress for each room and level A means of egress consists of three parts: exit access, exit and exit discharge.

Exit access is the path from any location within a building to an exit. An exit is a door leading to the outside or an enclosed exit stairway. Exit discharge is the path from the exit to the public way.

The code provides limits on: The minimum number of exits from a room or a story The maximum travel path (egress distance) from a room or a story The minimum width of the exit corridors, stairs and doors.

". . . where two or more occupancies utilize portions of the same means of egress system, those egress components shall meet the more stringent requirements of all occupancies that are served." IBC 2015, 1004.6

2.1 Determine the minimum number of exits criteria 2.1.1 Criteria for one exit (IBC Table 1006.2.1):

For One Exit:

Max. Occ. Max. Common

Occ.

Load Egress Dist, ft

A

49

75

B

49

100

M

49

75

Therefore, use Occ A for One Exit Criteria

Note: These criteria will be used in the Table on Pg. 6 to determine if a room requires more than one exit.

Common path of egress travel is "that portion of the exit travel distance measured from the most remote point within a story to that point where the occupants have separate and distinct access to two exits or exit access doorways."

Max_Occ_Load

49

Max_Egress_Distance, ft

75

2.1.2 Criteria for three or four exits (IBC 1006.2.1.1): If occupant load = 501 to 1000, use 3 exits If occupant load > 1000, use 4 exits

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Example

2.2 Determine the Maximum Egress Travel Distance for each level

For Each Story:

Max. Egress

Occ. Dist, ft

A

250

B

300

M

250

Therefore, use Occ A for Story Egress Criteria

Max. Allow. Egress Distance 250 ft

2.3 Determine the minimum egress width criteria for doors, corridors and stairs. Minimum widths are specified by component and by occupant load.

2.3.1 Minimum egress width criteria for components

Min. door width = 32 inches (IBC 2015 1010.1.1) Min. corridor width = 36 inches if occupant load < 50, else = 44 inches (IBC 2015 Table 1020.2) Min. stair width = 36 inches if occupant load < 50, else = 44 inches (IBC 2015 1011.2)

Min. stair width = 48" to be considered an accessible (to individuals with disabilities) means of egress (IBC 2015 1009.3). 38" stair width is not required for buildings equipped throughout with an automatic sprinkler system.

2.3.2 Minimum egress width criteria based on occupant load Corridors and Doors: min. total egress width = 0.2 inches / occupant Stairs: min. total egress width = 0.3 inches / occupant, (= 0.2 inches / occupant if automatic sprinkler and emergency voice/alarm system

". . . the loss of any one exit . . . shall not reduce the available width to less than 50% of the required width" (IBC 2015 1005.5).

2.4 For each space (room and level), calculate the occupant load, then calculate

The minimum number of exits The minimum total exit width

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Example

Table 1. Occupant loads, Required No. of Exits and Required Total Egress Widths

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Example

Typical calcs for Row 1 (Room 1001) of Table 1 on Pg 6: Occupancy Load Function = "Mercantile" from IBC 2015 Tabale 1004.1.2. Occupancy Load Factor = 60 sf per occupant from IBC 2015 Tabale 1004.1.2. Occupant Load = (Occ. Load Factor) ( Area) = ( 60 sf / occ ) ( 7462 sf ) = 125 occupants

Max. common egress distance = 96 ft.

Min. No. Exits: Occ. Load = 125 > 49 = max. occ. load for one exit. Therefore need more than one exit Egress Distance = 96 ft > 75 ft = max. egress distance for one exit. Therefore need more than one exit.

Occ. Load = 125 < 500 = max. occ. load for two exits. Therefore, min. no. exits for Room 1001 = 2

Min. Total Egress Width: Min. width = (0.2 "/occ.) x (125 occ.),

Min. egress width for Room 1001 = 25.0 inches

Typical calcs. for Level 2 of Table 1: Occupant Load = sum of occupant loads from all rooms on Level 2 = 176

Min. No. Exits: Occupancy Category = A-2 (most stringent), therefore one exit not allowed, IBC 2015 Table 1006.3.2(2) Occ. Load = 176 < 500, therefore do not need 3 exits. Min. No. Exits for Level 2 = 2 exits

Min. Total Egress Width: Min. width = (0.2 "/occ.) x (176 occ.),

Min. total egress width for Level 2 = 28 inches

Max. Egress Distance = 250 ft

Min. stair width = maximum of:

o (0.2"/Occupant) (Occupant Load) = 14.2" o 44" since Occ. Load > 50 o 48" for stairs to be "accessible" if not sprinklered

(IBC 2015 1009.3)

Min. stair width = 44"

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