Failure Criteria Compartmentation BCA Type A Fire resisting construction Fire behaviour

AUSTRALIAN STANDARD - AS 1530.4

  • SECTION 1. SCOPE AND GENERAL
  • SECTION 2. GENERAL REQUIREMENTS
  • SECTION 3. WALLS AND PARTITIONS
  • SECTION 4. FLOORS, ROOFS, FLOOR/CEILING SYSTEMS ANDROOF/CEILING SYSTEMS
  • SECTION 5. COLUMNS
  • SECTION 6  BEAMS, GIRDERS AND TRUSSES
  • SECTION 7. DOORSETS, SHUTTER ASSEMBLIES AND DAMPER ASSEMBLIES
  • SECTION 8. GLAZING
  • SECTION 9.  AIR DUCTS
  • SECTION 10.  ELEMENTS PENETRATED BY SERVICES
APPENDIX A.   RADIANT HEAT FLUX MEASUREMENTS

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AS 1530.4 – 2.11 Criteria of Failure

Loss of loadbearing capacity:

Limit or rate of deflection:
For flexural elements: D = L/20 * D = L2/9000d, * not before L30 is exceeded
For vertical elements: no specific requirements
d = distance from top structural section to bottom design tension zone

Loss of integrity:

Failure upon collapse when cracks, fissure or other openings through which flames or hot gases can pass occur

Loss of insulation:

Temperature rise:  +140°C average or,
                              +180°C max.

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PART C2 COMPARTMENTATION AND SEPARATION


Passive fire protection deals with the design of a building for adequate load bearing resistance and for limiting fire spread under fire conditions. Structural Fire Engineering is generally categorized in this discipline.

Fire Protection Engineering

Fire Protection Engineering comprises active and passive ways of providing satisfactory protection level to buildings and/or its contents from fires.

Sound design for guaranteeing fire safety of buildings

Design Specifications
  • Layout of the facility
  • Construction materials
  • Potential ventilation openings
  • Interconnections among compartments
  • Location of concealed spaces
  • Proposed egress routes
  • Anticipated fuel load (type & quantity)
  • Functions in the building
  • Passive fire protection systems
  • Active fire protection systems
  • Occupant load and characteristics
Failure Criteria for Compartmentation
AS 1530.4 – 2.11 Criteria of Failure
Compartment Failure or Failure of the Enclosure??
  • Criteria for compartment failure or structural failure as given in Standardised test requirements provide a means of ranking the performance of materials and products under a specific set of conditions.
  • The objective of defining a compartment is to prevent fire spread. In dealing with real fires in real buildings we should therefore dispense with the traditional approach of defining a compartment but quantify the ability of fire to spread from an enclosure.
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Building Code of Australia

PART C1 FIRE RESISTANCE AND STABILITY
Fire resistant Construction

Type of construction - not to be confused with building class, this determines the
level of fire resistance particular elements of the building must achieve.
Definition of Types
  • Type A
  • Type B
  • Type C

    • The BCA Deemed to Satisfy provisions addresses
    Type A, B and C constructions are relating to the fire performance of buildings.
Table C1.1 TYPE OF CONSTRUCTION REQUIRED

C1.1  Type of construction required

  Rise in storeys   Class of building
  2, 3, 9   5, 6, 7, 8
   4 OR MORE   A   A
    3   A
  B
    2   B   C
    1   C
  C

The minimum Type of fire-resisting construction of a building must be that specified in Table C1.1 and Specification C1.1, except as allowed for—
(i)         certain Class 2, 3 or 9c buildings in C1.5; and
(ii)        *  *  *  *  *
(iii)       open spectator stands and indoor sports stadiums in C1.7.
(iv)       *  *  *  *  *

Type A construction is the most fire-resistant and Type C the least fire-resistant of the Types of construction.

The classification of buildings and the type of construction can vary from the standard model depicted in the tables. Concessions can be provided that change the type of construction. The concessions can relate to the design of the building, its size, and the number of escapes.

BCA extract

3  TYPE A - FIRE-RESISTING CONSTRUCTION

Fire-resistance of building elements. In a building required to be of Type A construction—
(a)    each building element listed in Table 3 and any beam or column incorporated in it, must have an FRL not less than that listed in the Table for the particular Class of  building concerned; and
(b)    external walls, common walls and the flooring and floor framing of lift pits must be non-combustible; and
(c)    any internal wall required to have an FRL with respect to integrity and insulation must extend to—
              (i)       the underside of the floor next above; or
              (ii)      the underside of a roof complying with Table 3; or
              (iii)     if under Clause 3.5 the roof is not required to comply with Table 3, the underside of the non-combustible roof covering and, except for roof battens  with dimensions of 75 mm x 50 mm or less or roof sarking, must not be crossed by timber or other combustible building elements; or
              (iv)     a ceiling that is immediately below the roof and has a resistance to the incipient spread of fire to the roof space between the ceiling and the roof of not less than 60 minutes; and
(d)    a load bearing internal wall and a load bearing fire wall (including those that are part of a load bearing shaft) must be of concrete or masonry; and
(e)    a non- load bearing—
              (i)       internal wall required to be fire-resisting; and
              (ii)      lift, ventilating, pipe, garbage, or similar shaft that is not for the discharge of hot products of combustion, must be of non-combustible construction; and
(f)     the FRLs specified in Table 3 for an external column apply also to those parts of an internal column that face and are within 1.5 m of a window and are exposed through that window to a fire-source feature.


4.  TYPE B - FIRE-RESISTING CONSTRUCTION

Fire- resistance of building elementsIn a building required to be of Type B construction—
(a)        each building element listed in Table 4, and any beam or column incorporated in it, must have an FRL not less than that listed in the Table for the particular Class of building concerned; and


(b)    the external walls, common walls, and the flooring and floor framing in any lift pit, must be non-combustible; and
(c)    if a stair shaft supports any floor or a structural part of it—and
(d)    any internal wall which is required to have an FRL with respect to integrity and insulation,   except a wall that bounds a sole-occupancy unit in the topmost (or only) storey and there is only one unit in that storey, must extend to— and
(e)    a loadbearing internal wall and a loadbearing fire wall (including those that are part of a loadbearing shaft ) must be of concrete or masonry; and a non- loadbearing internal wall required to be fire-resisting must be of non-combustible  construction; and
(f)     in a Class 5, 6, 7, 8 or 9 building, in the storey immediately below the roof, internal columns and internal walls other than fire walls and shaft walls, need not comply with Table 4; and
        lift, subject to C2.10, ventilating, pipe, garbage, and similar shafts which are not for the discharge of hot products of combustion and not loadbearing, must be of non-combustible construction in—and
(g)    in a Class 2 or 3 building, except where within the one sole-occupancy unit, or a Class 9a health-care building or a Class 9b building, a floor separating storeys or above a space for the accommodation of motor vehicles or used for storage or any other ancillary purpose

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SPECIFICATION C1.1     FIRE-RESISTING CONSTRUCTION

GENERAL REQUIREMENTS
2.1     Exposure to fire-source features
 (a)     A part of a building element is exposed to a fire-source feature if any of the  horizontals  traight lines between that part and the fire-source feature, or vertical projection of the feature, is not obstructed by another part of the building that—
              (i)       has an FRL of not less than 30/–/–; and
              (ii)    is neither transparent nor translucent.
 (b)     A part of a building element is not exposed to a fire-source feature if the fire-source feature is—
              (i)     an external wall of another building that stands on the allotment and the part concerned is more than 15 m above the highest part of thatexternal wall; or
              (ii)    a side or rear boundary of the allotment and the part concerned is below the level of the finished ground at every relevant part of the boundary concerned.
 (c) If various distances apply for different parts of a building element—
               (i)    the entire element must have the FRL applicable to that part having the least distance between itself and the relevant fire-source feature; or
              (ii)    each part of the element must have the FRL applicable according to its individual distance from the relevant fire-source feature, but this provision does not override or permit any exemption from Clause 2.2.

Fire protection for a support of another part     
 (a)     Where a part of a building required to have an FRL depends upon direct vertical or lateral support from another part to maintain its FRL, that supporting part, subject to (b), must—
              (i)     have an FRL not less than that required by other provisions of this Specification; and
              (ii)    if located within the same fire compartment as the part it supports have an FRL in respect of structural adequacy the greater of that required—
                    (A) for the supporting part itself; and
                      (B) for the part it supports; and
              (iii)   be non-combustible—
                       (A)if required by other provisions of this Specification; or
                       (B)if the part it supports is required to be non-combustible.
 (b)     The following building elements need not comply with(a) (ii) and (a) (iii)(B):
              (i)     An element providing lateral support to an external wall complying with Clause 5.1(b) or C1.11.
          (ii)        An element providing support within a carpark and complying with Clause 3.9, 4.2
(iii)       A roof providing lateral support in a building—
                      (A)of Type A construction if it complies with Clause 3.5(a), (b) or (d); and
                      (B)of Type B and C construction.
          (iv)       A column providing lateral support to a wall where the column complies with Clause 2.5(a) and (b).
          (v)        An element providing lateral support to a fire wall or fire-resisting wall, provided the wall is supported on both sides and failure of the element on one side does not affect the fire performance of the wall.

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Fire behaviour of steel members penetrating concrete walls

The measurement of heat release rate (HRR) and smoke production rate (SPR) are direct indicators of the fire hazard. The growth of the HRR enables a lining material to be classified with respect to time based on if or when flashover occurs. The measurements of gas species, percentage of flame spread area over the lining surface, and compartment temperatures and smoke layer height, are compared to confirm that the conditions generated are consistent with the primary parameters of HRR and SPR and accurately reflect the fire hazard

3.5 Roof: Concession
A roof need not comply with Table 3 if its covering is non-combustible and the building—
(a)        has a sprinkler system complying with Specification E1.5 installed throughout; or
(b)        has a rise in storeys of 3 or less; or
(c)        is of Class 2 or 3; or
(d)        has an effective height of not more than 25 m and the ceiling immediately below the roof has a resistance to the incipient spread of fire to the roof space of not
             less than 60 minutes.

Key Factors for Time-Equivalent Analysis

When a fire reaches a stage where there is full involvement of the combustibles within a compartment (known as flashover), the intensity of the heat in the hot smoke layer will cause glazing and non-fire resisting facades to fail, allowing hot gases to escape (see Figure below).


Similarly, openings to atria will also allow hot gases to escape. The temperatures reached in a compartment and the duration of a fire depend on natural ventilation through openings to atria and glazing or non-fire resisting facades that fail in a fire.

Mechanism of Fire Spread

  • Conduction
                (Heat transfer to another body or within a body by direct contact.)
  • Radiation
                (Heat transfer by way of electromagnetic energy.)
  • Convection
                (Heat transfer by circulation within a medium, such as a gas or a liquid.)
  • Pyrolysis
                (The transformation of a compound into one or more other substances by heat alone. Pyrolysis often precedes combustion. Irreversible chemical decomposition caused by heat, usually without combustion.)
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