Fire safety — Building Code Methods

Fire safety - Building Code Methods

Fire Safety and Building Code Methods

Jonathan Ochshorn

2009 Jonathan Ochshorn.

Based on International Building Code 2009: IBC (latest version) can be found online, Cornell students only, by entering MADCAD in the title field of a library search .

I. Occupancy (what the building is used for)

  • A. Refer to Chapter 3 (Use and Occupancy Classification)

    1. A = assembly — lecture rooms, auditoriums, stadia, etc.
    2. B = buisness — office buildings, banks, outpatient clinics, colleges and universities, etc.
    3. E = educational — schools (grade 12 or less), daycare
    4. F = factory and industrial
    5. H = high hazard — buildings containing hazardous material
    6. I = institutional — nurseries, health care, jails
    7. M = mercantile — merchandise sales (department stores, markets, service stations, etc.)
    8. R = residential — dwellings, hotels, apartment houses
    9. S = storage — storage, including storage of hazardous materials
    10. U = utility and miscellaneous — accessory types of structures like garages, towers, tanks

II. Construction type

  • A. Refer to Table 601 (Fire-Resistance Rating Requirements); two basic categories are:

    1. Types I and II: basically non-combustible, with some exceptions
    2. Types III, IV and V: allow combustible material (i.e. wood)
    3. Fire safety - Building Code Methods
    4. Sprinklers: Note that sprinklers may substitute for 1-hr construction (note «d», Table 601) if they are (1) not elsewhere required, or (2) used for an area or height increase — see below.

  • B. Types I and II fire-resistive

    • noncombustible materials (concrete, masonry, steel)
    • substantial fire-resistance ratings (up to 3hrs)
    • differences:

      • type I —fewer height or area limits, but 2-3 hr. fire-resistance for structure;
      • type II — substantially lower height limits; other limits on floor area and number of stories;
      • less fire resistance required for type II structures means less cost.

  • C. Type II A, B [Type B is «unprotected»]

    • noncombustible materials;
    • less substantial or no [type II B] fire-resistance ratings;
    • smaller floor areas, heights, number of stories allowed (mostly 4 stories allowed).

  • D. Type III A, B

    • noncombustible exterior walls of masonry or concrete with anything else inside;
    • similar limits as Type II A, B (since exterior walls have such a high f.r.-rating);
    • was known as «ordinary» construction.

  • E. Type IV

    • noncombustible exterior walls of masonry or concrete with certain combustible materials inside;
    • minimum dimensions on wood structure: 8″ min. for columns; 6×10 minimum for beams;
    • no concealed ceiling spaces, etc.
    • was known as «heavy timber» construction.
    • Can be used in roof construction where 1-hour fire-resistance (or less) is required.

  • F. Type V A, B

    • basically light wood framing;
    • greatest limitations on area, heights, etc. where permitted at all.

III. Other questions:

  • A. Exterior wall fire resistance (Table 602 ) depends on:

    1. Occupancy
    2. Construction type
    3. Distance to property line (fire separation distance)
    4. Whether walls are bearing or nonbearing (for bearing walls, see also Table 601 )

  • B. Openings in exterior walls (Table 705.8 ) depend on:

    1. Distance to property line (fire separation distance)
    2. Classification of opening (protected or unprotected)
    3. Whether building is sprinklered (705.8.2 )

  • C. Required separation in buildings of mixed occupancy (Table 508.4 ) depends on:

    1. Occupancies

  • D. Basic allowable building heights and (single floor) floor areas (Table 503 ) depend on:

    1. Occupancy
    2. Construction type
    3. Sprinklers: Note that height may be increased 20 ft. and maximum number of stories increased by 1 story when sprinklers conforming to NFPA 13 are used (see IBC sec. 903.3.1.1).

  • E. Basic building area can be increased for frontage, sprinklers, and numbers of stories as follows:

    Allowable area per floor, Aa = At (1.0 + If + Is ) where At is the «tabular» value found in Table 503, and If and Is are as defined below. See Section 506, Equation 5-1.

    For unsprinklered buildings up to 3 stories, and for sprinklered buildings of with any number of stories, the maximum total allowable building area is the allowable area for a single floor times the number of stories (but note that the sprinkler coefficient must correspond to the total number of stories). For unsprinklered buildings with more than 3 stories, the maximum allowable total building area = the allowable area per floor times three. Note that in all cases, any floor cannot exceed the allowable floor area computed above. There is an exception for Group R buildings with so-called NFPA 13R sprinklers: for such buildings, limited to 4 stories, the maximum total building area is the allowable area for a single floor times the number of stories (but note that no more than 4 stories are allowed, and that the sprinkler increase, Is. is not permitted when the sprinklers are designed according to NFPA 13R. If the sprinklers were to be designed according to NFPA 13, instead of 13R, the maximum allowable building area would be limited to 3 times the allowable single floor area (even for a 4-story building), but the allowable single floor area would be increased according to the coefficient Is .

    Where there is no frontage increase, or a building is unsprinklered, the values of If or Is are taken as zero.

    1. If = Frontage increase coefficient = (F/P — 0.25)(W/30) where

    • F = portion of building perimeter fronting on public way or open space with 20 ft. minimum width; note that if F is less than 25% of the total building perimeter, If is taken as zero.
    • P = total building perimeter;
    • W = Weighted average of open space/public way width in front of building:
      • Only count widths that are greater or equal to 20 ft;
      • Use 30 ft. for all widths that are greater than 30 ft, except as described below under «Unlimited Area Buildings»;
      • Open space must be on building lot or reserved for public use; also must be connected to a street or «fire lane,»
      • Widths fronting right-of-ways (ROWs) can be measured to the far side of the ROW rather than to the near side (i.e, rather than to the property line).
    • Sample calculation of frontage increase coefficient (see site plan below):

    F = 60 + 100 + 60 = 220 ft. (Note that only sides A, B, and C are counted because the width of side D is less than 20 ft. Also note that the width of side C is measured to the centerline of the right-of-way.)

    P = 60 + 100 + 60 + 100 = 320 ft.

    W = [25(60) + 30(100) + 30(60)] / (60 + 100 + 60) = 28.64 ft. (Note that actual widths greater than 30 feet are counted as 30 ft. in the weighted average, and that only widths of 20 ft. or more are included.)

    If = (220/320 — 0.25)(28.64/30) = 0.42 .

2. Is = Sprinkler increase coefficient = 3 for 1-story buildings and 2 for multi-story buildings, when sprinklers conform to NFPA 13.

  • Note that height and story increases can still be taken with sprinklers in addition to this area increase;
  • There are exceptions for H occupancies: see details in IBC Section 506.3;
  • Also, this increase cannot be taken when sprinklers are used per note «e» of Table 601 (i.e. to substitute for 1-hr. fire-resistiver construction).

3. Unlimited area buildings are permitted where the minimum yard distance on all sides is 60 feet, and occupancy, sprinklers, and number of stories meet the criteria in the following table:

Occupancies

Sprinklers required?


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