Part C2 Compartmentation and separation

Where a solution is proposed to comply with the Deemed-to-Satisfy Provisions, C2.0 clarifies that for most buildings compliance with Parts C1, C2 and C3 will achieve compliance with CP1 to CP9. The exceptions to this general rule are set out below:

• If the building contains an atrium, it must comply with Part G3 in addition to Parts C1, C2 and C3.
• A building which comprises a theatre, stage or public hall must comply with Part H1 in addition to Parts C1, C2 and C3.
• If the building contains an atrium and one or more of a theatre, stage or public hall, it must comply with Parts C1, C2, C3, G3 and H1.
• Farm sheds must comply with Part H3 in addition to Parts C1, C2 and C3.

Where a Performance Solution is proposed, the relevant Performance Requirements must be determined in accordance with A2.2(3) and A2.4(3) as applicable. (See commentary on Part A2).

The floor area limitations of Part C2 do not apply to a carpark containing a sprinkler system complying with Specification E1.5 (other than a FPAA101D or FPAA 101H system), an open-deck carpark or an open spectator stand.

The separation requirements of potentially explosive batteries from the rest of the building contained in C2.12(a)(v) do not apply to Class 8 electricity network substations. These batteries have inherent and specific protection, segregation and risk mitigation measures. They are housed within the substation, with other electrical equipment which the batteries are dedicated to support. The other ancillary building services in the substation are always kept separate from the batteries and further internal separation is not considered necessary.

Under C2.2(a) and Table C2.2, the allowable size of the fire compartment depends on two things. The first is the type of construction, which is a measure of a building’s ability to resist a fire. The second is the classification of the building, which is an indicator of a building’s potential fire load.

Under C2.2(b), machinery and plant rooms at the top of a building are not included in the calculation of a building’s floor area or volume of a fire compartment. The BCA assumes that such rooms represent a low risk to people in case of fire because of the generally:

• low fire load;
• low number of people who use them; and
• as the occupants of most buildings evacuate downwards, a fire in a plant room at the top of a building will generally not interfere with the ability to evacuate.

Under C2.2(c), in an atrium, the area of the atrium well above the floor of the atrium is excluded from the volume calculation because there is no space in which to store materials, thus it is assumed that it does not contribute to the fire load. See Part G3.

Table C2.2 allows sprinkler protected Class 9c buildings to have a maximum fire compartment size of—

• if the building is of Type A construction—8 000 m²; or
• if the building is of Type B construction—5 000 m²; or
• if the building is of Type C construction—3 000 m².

C2.2 makes no reference to the use of Table C2.2 for a building containing mixed classifications. The table specifies both the maximum allowable floor area and volume of certain fire compartments and atria.

To calculate the maximum permissible floor area component of the size limitations in Table C2.2, firstly take the percentage of each classification as a proportion of the actual floor area of the building.

Then, use this percentage to calculate the proportion of the maximum floor area permitted for that classification in Table C2.2 and then add each of those calculations together to come to a maximum permitted floor area for the combined classifications. This is illustrated in simpler terms in the example below.

Figure C2.2 Plan of building for above example

Under C2.3(a), a building with a floor area of 18 000 m² or less and a volume of 108 000 m³ or less is permitted to have fire compartments which exceed the requirements of Table C2.2, if it complies with the requirements outlined below as applicable:

• Where the building is either Class 7 or Class 8—
  • it contains no more than 2 storeys; and
  • it has an 18 m wide open space around the building complying with C2.4(a).
• Where the building is Class 5–9 (including Class 7 and Class 8), it contains a sprinkler system complying with Specification E1.5 and has vehicular access complying with C2.4(b).

Under C2.3(b), a building with a floor area of more than 18 000 m²or a volume of more than 108 000 m³ is permitted to have fire compartments which exceed the requirements of Table C2.2 if—

• it is protected with a sprinkler system complying with Specification E1.5; and
• it has vehicular access complying with C2.4(b).

C2.3 should be read in conjunction with the smoke hazard management systems required by Table E2.2a. The reason for this is that the smoke hazard management system will play an important part in occupant safety during a fire in large fire compartments.

Where there is more than one building on the allotment, each building may have fire compartments which exceed the requirements of Table C2.2, if each building complies with C2.3(a) or C2.3(b), or if the buildings are closer than 6 metres, they both must comply with C2.3(a) or C2.3(b), as applicable, as if they were one building.

If the buildings are separated by a fire wall complying with C2.7, the entire building, regardless of the level of fire compartmentation, must comply with C2.3(a) or C2.3(b), as applicable.

If more than two buildings are located on the same allotment and greater than 6 m apart, each individual building must comply with C2.3(a) or C2.3(b), as applicable.

The reason for the open space requirement is to minimise the risk of a fire spreading to another building.

C2.4(a) specifies the compliance criteria for the open space required under C2.3. The open space must be wholly within the allotment. However, the open space may also include everything except what is beyond a line drawn six metres from the farthest edge of a road, river or public place adjoining the allotment.

The open space must also include the vehicular access required by C2.4(b), not be used for storage or processing and not be built on, except as specified.

This provision requires the making of a “performance-style” judgement. It is the responsibility of the building proponent to satisfy the appropriate authority that any buildings on the open space will not unduly impede the activities of the fire brigade, nor add to the risk of fire spreading to a building on an adjoining allotment.

Figure C2.4 illustrates compliance with C2.4.

The reason for the fire brigade vehicular access is to enable the brigade to intervene to fight the fire, assist with evacuation, and stop the spread of a fire to another building. The vehicular access also provides other emergency services personnel, such as ambulance officers, with the ability to access the building as necessary.

C2.4(b) specifies the compliance criteria for the vehicular access required by Part C2.

The required vehicular access must have access from the public road system (see C2.4(b)(i)) and must have the width, height and loadbearing capacity to allow the passage in a forward direction around the entire building and parking of fire brigade vehicles (see C2.4(b)(ii) and (iv)).

It must also have the necessary pedestrian access to the building (see C2.4(b)(iii)). This access may be from a public road which otherwise complies with the various requirements of C2.4(b) (see C2.4(b)(v)).

To achieve compliance with these provisions it is advisable to check with the local fire brigade, due to the varying sizes and type of equipment and vehicles that may be required to fight a fire.

Figure C2.4 Examples of compliance with C2.4

It should be noted that C2.5(a) applies to Class 9a health-care buildings. C2.5(b) only applies to Class 9c buildings.

Residents or patients of Class 9a buildings are often unable to evacuate a building without assistance. They may be incapable of walking or bedridden. It is important to make sure that fire and smoke only affects small areas of the building.

C2.5(a)(i) requires compartmentation for the control of smoke and fire.

C2.5(a)(ii) and (v) make it necessary to separate potential sources of fire from any patient care area. C2.5(a)(ii) requires fire compartments in Class 9a buildings. An ancillary use area in C2.5(a)(v) is deemed to be an area where there are items of equipment or materials, that have a high potential fire hazard (high fire load or fire source).

C2.5(a)(iii) and (iv) require sub-compartmentation in certain areas to allow for the staged evacuation of patients from the building. Sub-compartmentation is considered to enhance evacuation procedures, which typically require assistance to be provided to evacuees by an adequate number of staff.

The requirements for smoke proof walls and doors are contained in Specification C2.5.

C2.5(a)(vi) provides examples of areas covered by (v).

Figure C2.5 illustrates one means of complying with C2.5.

The first part of the figure shows how the administrative area of a hospital has been separated from the patient care area by a fire wall because the patient care area has a floor area of 2000 m², the maximum permitted under C2.5(a)(i).

The second part of the figure shows how the ward area must be subdivided into areas with a maximum floor area of 1 000 m² by a wall with an FRL of 60/60/60.

Compliance with C2.5(a)(iv)(B) may require a floor in a Class 9a building of Type B construction to have a fire-resistance level (FRL). The reason for this is that it is important to inhibit the spread of fire between floors. Separation of storeys in a Class 9a building also requires any openings in external walls to be vertically separated in accordance with C2.6.

Residents of Class 9c buildings are often unable to evacuate without assistance. They may be incapable of walking or bedridden. It is therefore important to make sure that fire and smoke only affects small areas of the building, hence allowing residents sufficient time should evacuation be necessary.

C2.5(b)(ii) requires certain walls and floors in Class 9c buildings to have a fire-resistance level (FRL). The reason for this is that it is important to inhibit the spread of fire for resident and occupant safety.

C2.5(b)(iii) allows internal walls (other than one bounding a lift or stair shaft) to have an FRL of 60/–/– because the floor is required to have an FRL of 60/60/60. Note that the FRL is only required for structural adequacy because Table 4 only requires loadbearing walls in these situations to have an FRL with respect to structural adequacy. The lower FRL allowed by C2.5(b)(iii) recognises the effectiveness of the required sprinkler systems in Class 9c buildings.

The compartmentation required by fire rated and smoke proof walls for Class 9c buildings is similar to that required for Class 9a buildings.

The required compartmentation and sub-compartmentation of Class 9c buildings are to allow for the staged evacuation of residents from the building. However, successful evacuation usually depends on assistance being provided to evacuees by an adequate number of staff. The BCA provisions for Class 9c buildings are based on minimal on duty on-site staff being available at any time.

C2.5(b)(i) requires a Class 9c building to be subdivided into areas with a maximum area of 500 m² by smoke walls complying with Specification C2.5. No further subdivision of the fire compartments by smoke or fire rated walls is required. This recognises the benefits of sprinkler systems that must be installed in all Class 9c buildings.

An ancillary use area in C2.5(b)(iv) is deemed to be an area where there are items of equipment or materials that have a high potential fire hazard (high fire load or fire source). The reason these walls need only be smoke proof, whereas those in a Class 9a building must have an FRL, is that Class 9c buildings must be sprinkler protected.

C2.5(b)(v) provides examples of areas covered by (iv).

Figure C2.5 Plan showing one method of complying with C2.5(a) for Class 9a buildings

C2.6 generally applies to buildings of Type A construction and Class 9a buildings of Type B construction, because they are the only buildings required to provide fire separation between floors. This separation is achieved by the floor being required to have a fire-resistance level (FRL). It applies to openings above one another in different storeys if they are within a horizontal distance of 450 mm of each other.

It does not apply to:

• sprinkler protected buildings because the sprinklers should prevent the fire developing to the stage where it could spread to the floor above;
• openings in a fire-isolated stair shaft. This is because the stair shaft is not considered to be separate storeys and it is assumed that fire spread between floors will not occur via the stairway; or
• open-deck carparks and open spectator stands. This is because it is unlikely that fire would spread between floors in these types of buildings as their open construction allows the dissipation of the effects of fire.

In addition, Class 9a buildings of Type B construction require openings in external walls to be vertically separated in accordance with C2.6 as if the building was Type A construction (see C2.5(a)(iv)). This can be achieved either by the construction methods outlined below or the installation of sprinklers in the building. The reason for this is that it is important to inhibit the spread of fire between floors in Class 9a buildings.

C2.6 requires the vertical separation of openings in external walls (see C2.6(a) and (b)) of buildings of Type A construction which do not have a sprinkler system complying with Specification E1.5 (other than a FPAA101D or FPAA101H system). The vertical separation of openings can be achieved by either of the following methods:

• a non-combustible spandrel or other non-combustible vertical construction having an overall height of 900 mm or more, extending at least 600 mm or more above the upper surface of the intervening floor, and having an FRL of 60/60/60 (see C2.6(a)(i)) as shown in Figure C2.6(1); or
• a non-combustible horizontal projection having an outwards projection from the external face of the wall of 1 100 mm or more, an extension along the wall beyond the openings of at least 450 mm, and having an FRL of 60/60/60 (see C2.6(a)(iv)) as shown in Figure C2.6(2).

If the external wall of the building is a glass curtain wall, C2.6(a)(iii) contains specific provisions to stop or limit the spread of fire and smoke between the glass and the edge of the concrete floor. The details are shown in Figure C2.6(3).

Although it could be argued that the spandrel or vertical projection should have the same FRL as the floor separating the storeys, this has not been found to be necessary.

C2.6(c) explains the meaning of the term "window or other opening" as used in C2.6(a). Basically, the term is used to describe a part of the external wall which does not have an FRL of at least 60/60/60 to limit the spread of fire from one storey to another by passing out through the window or opening and then re-entering the building through a similar opening (i.e. one without an FRL of at least 60/60/60) on the storey above. Examples of such openings include:

• windows;
• glass curtain walls;
• non-fire rated panels; and
• other parts of the wall that do not have an FRL of at least 60/60/60.

Figure C2.6(1) Section showing use of spandrel to separate external window openings

Figure C2.6(2) Example showing use of slab or horizontal construction to separate external window openings

Figure C2.6(3) Section showing separation of external window openings in a curtain wall

C2.7(a) outlines how a fire wall is to be constructed.

C2.7(a)(i) sets out the required FRL of a fire wall. If any part adjoining the fire wall is required to have a higher FRL, the fire wall must achieve the higher FRL. The exception occurs if an adjoining part is an open-deck or sprinklered carpark that complies with the concessions set out in Table 3.9, 4.2 or 5.2 of Specification C1.

C2.7(a)(ii) requires all openings in fire walls to not reduce the required FRL of Specification C1.1 for the fire wall, except where permitted by Part C3. In effect, this provision is referring to:

• C3.5 for doorways in fire walls;
• C3.6 for sliding doors in fire walls;
• C3.7 if the fire wall forms separation required for horizontal exits; and
• C3.15 for openings for service penetrations.

Figure C2.7(1) Example of method of separating a building by a fire wall in accordance with C2.7(b)(ii)

C2.7(a)(iii) indicates which building elements are permitted to pass through or cross a fire wall and prohibits the use of any building element if it reduces the fire wall's FRL below that required. Hence, elements that pass through or cross a fire wall have to be part of the fire wall's tested prototype.

C2.7(a)(iii) grants an exemption to its requirements for small roof battens and roof sarking.

C2.7(b) indicates the extent a fire wall divides a building into separate buildings for the Deemed-to-Satisfy Provisions of Sections C, D and E (see Figure C2.7(1)).

The fire wall must extend through all storeys and similar spaces which are common to the subject parts of the building, and any adjoining part of the building, through to the underside of any roof covering (see C2.7(b)(ii)).

C2.7(b) outlines the requirements for the extent of a fire wall that separates adjoining parts of a building where the roofs are at different levels.

If buildings, with different roof levels divided by a fire wall, are to be treated as two separate buildings, the fire wall must extend up to the underside of the highest roof or not less than 6 m above the covering of the lowest roof.

Alternatively, C2.7(b) allows the fire wall not to extend 6 m above the lower roof if the roof to the lower level building:

• has the FRL prescribed for the fire wall by Specification C1.1 and no openings are located within 3 m of any wall located above the lower roof; or
• the lower roof is non-combustible and the part of the building below has a sprinkler system complying with Specification E1.5 (other than a FPAA101D or FPAA101H system) installed.

C2.7(c) clarifies that a fire wall built in accordance with C2.7(a) can be considered to divide a building into different fire compartments for the purpose of Sections C, D and E (see Figure 2.7(2)).

Figure C2.7(2) Example of a method of separating a building into fire compartments by a fire wall in accordance with C2.7(c)

For a fire wall to compartment a building it must extend to the underside of any roof covering or between floors that have an equivalent FRL to the fire wall.

If the building is being separated into fire compartments by a fire wall have different roof levels there is no requirement to extend the fire wall to the underside of the higher roof level or above the lower roof level. This is because the fire wall serves as a means to limit the floor area of the building. When a fire wall is applied in this case, the building cannot be treated as two separate buildings for the purpose of Sections C, D and E of the BCA.

Figure C2.7(2) illustrates the case where two fire walls divide storeys but do not align, therefore not meeting the requirements of C2.7(b). In this case, the building cannot be regarded as two buildings divided by a fire wall.

Figure C2.7(3) illustrates a circumstance where a fire wall can be an external wall. This is important to note because of a possible reading of the definition of “fire wall” which indicates that a fire wall would always be an internal wall. For the purposes of Sections C, D and E, the separated building is regarded as two buildings.

The fire-resistance level (FRL) required for building elements varies, depending on the expected fire load. This load is measured in the BCA by the building classification. With these differing FRLs, it is important that a fire in one classification does not cause the failure of building elements in any other classification.

There are two options to stop a fire spreading from one classification to another classification on the same storey:

• use the highest of the two fire-resistance levels (FRLs) required for each building element in that storey (see C2.8(a)); or
• place a fire wall between the two different classifications (see C2.8(b) and (c)). In a building of mixed classification C2.8(b) clarifies that for Type A and Type B construction the FRL is the higher of that specified in Table 3 or 4 but for Type C construction it is the FRL specified in Table 5. This is because the FRL for firewalls in Type C construction is the same for all Classes.

Figure C2.8(1) illustrates some examples of fire walls separating different classifications within the same storey of a building. In the first diagram, the public corridor must be fire-separated from the Class 6 part (as shown) or the Class 5 part to achieve total fire-separation between the different classifications. If a doorway is located in the fire wall, it must comply with C3.5.

Figure C2.7(3) Example of fire wall used as an external wall to separate a building in accordance with C2.7(b)(iii)

Figure C2.8(1) Examples of fire wall separating different classifications in a building of Type A construction

The diagrams in Figure C2.8(2) illustrate examples of fire walls separating different classifications within the same storey of a multi-storey building and floors separating different classifications.

Figure C2.8(2) Examples of fire walls and floors separating different classifications in a building of Type A construction

C2.9 specifies the required separation between parts of a building which are of a different classification, situated one above the other.

The aim of C2.9 is for the fire load of a storey to determine the fire protection of the floor above it. A fire on one storey will affect the storey above to a greater degree than any storey below.

C2.9(a) sets out the requirements for buildings of Type A construction. Figure C2.9 illustrates an example of the required fire-resistance level (FRL) of floors in a 3 storey building required to be of Type A construction.

C2.9(b) sets out the requirements for buildings of Type B and Type C construction. However, note that C2.9(b ) is only applicable where one of the parts being separated is Class 2, Class 3 or Class 4 and Specification C1.1 Clauses 4.1(i) and 5.1(e) require floors to be protected if the building is Class 2, 3 or 9.

Figure C2.9 Example of floors separating different classifications in a building of Type A construction

The approach adopted in C2.10 for lift shafts is similar to that adopted by the BCA for stairway shafts.

C2.10 applies to all classes of buildings and specifies the protection requirements for openings both for lift landing doors and services.

In any building required to be of Type A or B construction, having a lift connecting more than 2 storeys or more than 3 storeys if the building is sprinklered (other than lifts that are wholly within an atrium), the lift must be in an enclosed shaft separated from the rest of the building.

The lift shaft walls in a building of Type A construction must have the relevant fire-resistance level (FRL) prescribed by Table 3 of Specification C1.1. It does not matter what Class the building is, nor whether the shaft walls are loadbearing.

In a building required to be of Type B construction, the lift shaft walls must have the relevant FRL prescribed by Table 4 of Specification C1.1 if they are loadbearing. If the lift shaft walls are non-loadbearing they must be of non-combustible construction.

As all emergency lifts are required to be fire separated from the remainder of the building, C2.10(c) clarifies that the lift shaft is to have an FRL of not less than 120/120/120.

C2.10(d) only applies to fire-isolated lift shafts. Lift landing doors and indicator panels are covered by C3.10. Openings for other services must comply with any other appropriate provisions in Part C3.

If a lift is wholly in an atrium, it is not required to be in a fire-isolated shaft. This is because the atrium comprises a single fire compartment.

Any lift in a patient care area in a Class 9a building, or a resident use area in a Class 9c building is to be in a fire-isolated shaft. In a Class 9a or 9c building that is required to be of Type A or B construction it is to have an FRL of 120/120/120. In a Class 9a or 9c building of Type C construction the shaft is to have an FRL of 60/60/60.

Apart from emergency lifts and lifts in patient care and resident use areas, lifts need not be in a fire-isolated shaft if the building is of Type C construction. This is because such buildings are not required to have fire-rated floors or any fire compartmentation between storeys.

Lift shafts do not offer the same fire protection to occupants as fire-isolated stairway shafts. This is because lift landing doors to shafts have no insulation properties and do not seal against smoke to the same extent as fire doors to stairway shafts. Also, many lift over-runs are places where rubbish or other combustible materials may accumulate and are therefore potential fire-sources.

C2.12 is part of the Deemed-to-Satisfy Provisions for CP6 and CP7.

The types of equipment referred to in C2.12(a)(i) and (ii) and C2.12(c) need to continue to operate during an emergency, such as a fire. It is therefore important to stop the spread of fire to this equipment.

The requirement under C2.12(c) that on-site fire pumps comply with E1.3, rather than C2.12(d), recognises the importance of this equipment to fire-fighting.

The type of equipment referred to in C2.12(a)(iv) have a high explosive potential. The high temperatures and pressures associated with a boiler requires consideration for protection as opposed to a normal water heater. It is important that any fire in this type of equipment does not spread to other parts of the building.

Batteries referred to in C2.12(a)(v) have the potential to contain high levels of embodied energy. In a fire event, this embodied energy can contribute to fire propagation and can be difficult to extinguish. Reference to “installed in the building” means batteries hard wired into the building. This includes batteries used to provide power supply for fire safety equipment, lifts, pumps, energy storage from renewable energy sources and the like. It does not include batteries associated with removable data infrastructure, vehicles or batteries that can be readily removed or relocated (such as plug in UPS batteries).

Not all equipment is required to be protected. Examples are listed in C2.12(b). This equipment is either designed to withstand high temperatures during a fire, or is required to be protected by other parts of the BCA.

Under C2.12(d), the minimum fire-resistance level (FRL) for construction used to separate the equipment listed in C2.12(a) from the remainder of the building is 120/120/120, with –/120/30 fire doors. However, if Specification C1.1 (particularly Tables 3, 4 or 5) requires a higher FRL, then that higher FRL applies.

C2.13 is part of the Deemed-to-Satisfy Provisions for CP6 and CP7.

Certain types of electrical equipment have a high potential for explosion as well as fire. C2.13(a) requires that the doorways to sub-stations be protected with –/120/30 fire doors to avoid the spread of any fire from the electrical equipment.

Some State and Territory authorities may have additional requirements for the construction of electricity sub-stations. See relevant State or Territory Appendix to the BCA.

To enable the required emergency equipment to continue to operate during any emergency, the following must be achieved:

• The main switchboard referred to in C2.13(b) must be separated from other parts of the building by construction having a fire-resistance level (FRL) of 120/120/120, and any door openings protected with –/120/30 fire doors.
• The electrical conductors referred to in C2.13(c) must comply with the appropriate sections of AS/NZS 3013—Wiring installations—Wiring systems for specific applications, or be protected by fire rated construction with an FRL of 120/120/120.

Emergency equipment is considered sustained by a main switchboard when the emergency equipment does not rely on:

• battery backup; or
• an alternative power source running through the main switchboard,

when operating in the emergency mode.

ABCB funded research determined that providing physical segregation between non-emergency equipment switchgear and emergency equipment switchgear reduces the impact of potential damage from fire by 40%. It is essential that this equipment continue to operate during a fire. C2.13(d) therefore requires the emergency equipment to be segregated from the other equipment in all switchboards by metal partitions designed to prevent the spread of any fault from the non-emergency equipment to the emergency equipment.

C2.13(e) lists the emergency equipment required by C2.13(d) to be separated from non-emergency equipment in a switchboard.

In a building fire, certain people are subject to greater risks than others, for example, the very young, elderly, people with disabilities, and those who are asleep.

In a Class 2 or Class 3 building there is a very high risk that building occupants will be asleep when a fire occurs. It is important that they be able to safely evacuate the building. To assist in the safe evacuation, long public corridors should not become smoke logged.

C2.14 therefore requires the division of the public corridors into 40 metre lengths, by smoke walls and smoke doors. The details of the smoke walls are set out in Specification C2.5, and details for the smoke doors are set out in Specification C3.4.

The measurement of the length of the public corridor includes the sum of all connected corridor lengths that are continuous within a separate storey, smoke compartment or fire compartment.