NCC 2022 Volume One - Building Code of Australia Class 2 to 9 buildings
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31

Specification 31 Fire and smoke control systems in buildings containing atriums

Specification 31 Fire and smoke control systems in buildings containing atriums

This Specification sets out the requirements for the design and operation of systems of fire and smoke control in buildings containing an atrium.

To clarify that Specification 31 includes the requirements for fire and smoke control systems in buildings with an atrium.

Specification 31 includes the requirements for fire and smoke control systems in buildings containing an atrium.

Where a sprinkler system is required, it must be installed in the whole building, not just that part in which the atrium is located.

Automatic fire sprinkler system

A sprinkler system (other than a FPAA101D or FPAA101H system) complying with Specification 17 must be installed in every building containing an atrium, except where varied or superseded by this Specification.

To set out the general requirements for the installation of a suitable sprinkler system in a building containing an atrium.

Generally, a sprinkler system must comply with Specification 17. S31C3 to S31C6 sets out additional requirements for sprinklers in a building containing an atrium.

If any conflict exists between Specification 17 and S31C3 to S31C6, then S31C3 to S31C6 take precedence.

(1) A roof of an atrium which does not have the FRL prescribed in Specification 5 or the Deemed-to-Satisfy Provisions of Part C3 must be protected by automatic sprinklers arranged to wet both the covering membrane and supporting structure if the roof is—

  1. less than 12 m above the floor of the atrium or the floor of the highest storey where the bounding construction is set back more than 3.5 m from the atrium well if a Class 2, 3, 5 or 9 part of a building is open to the atrium; or
  2. less than 20 m above the floor of the atrium or the floor of the highest storey where the bounding construction is set back more than 3.5 m from the atrium well if a Class 6, 7 or 8 part of a building is open to the atrium.

(2) The temperature rating of sprinkler heads required by (1) must be within the range 79°C – 100°C

To set out the roof protection requirements for a building containing an atrium.

S31C3 requires smoke extraction through the roof, or near the top of the atrium. It is therefore important that the roof remains in place during a fire and does not allow the re-circulation of smoke. To achieve this, G3D6 requires the roof:

  • to have the FRL required by Table S5C11g of Specification 5; or
  • structure and membrane to be protected by a sprinkler system (other than a FPAA101D or FPAA101H system).

When the roof is required to have an FRL, G3D6(a) does not allow the use of the concessions contained in S5C14, S5C15 or S5C16 for the roof of the atrium.

The sprinkler protection requirement only applies to a roof located in an area where a fire could affect its integrity. The distances stated in S31C3(a) and (b) differ because of the different fire loads assumed in the different Classes of building. The heights of the atrium roof have been selected as those beyond which a smoke plume produced by a typical fire would no longer be hot enough to damage an unprotected roof.

The sprinkler heads need only be arranged to give a wetting effect to both the underside of the roof membrane and any part of the supporting structure.

The higher temperature rating of the sprinkler heads is to make sure they do not falsely discharge due to the potentially higher normal temperatures under an atrium roof, especially if a glass or translucent roof is used (as is common practice).

S31C3 requires smoke extraction through the roof, or near the top of an atrium. The smoke extraction is required to be by mechanical exhaust or by smoke and heat vents.

Figure S31C3 illustrates the alternative protection of an atrium roof.
 

Figure S31C3: Alternative protection for atrium roof

Image
Figure S31C3: Alternative protection for atrium roof

The floor of the atrium must be protected by sprinklers with—

  1. the use of sidewall pattern sprinkler heads together with overhead sprinklers where dictated by the dimensions of the atrium; and
  2. sprinkler heads of the quick response type.

To set out fire protection requirements for atrium floors (i.e. at the lowest level of the atrium).

Because of the height of the roof in an atrium, the sprinklers protecting it are unlikely to be effective at the lowest level of the atrium. Additional sprinklers are therefore normally required to protect that level, as this area is normally a large open space, and is potentially the primary source of a major fire. Adequate protection of the floor often requires the use of sidewall sprinkler heads, as required by S31C4(a). S31C4(a) requires a “performance-type” decision as to the types of sprinklers (sidewall and overhead) and their combination.

Because of the additional fire hazard associated with atriums, S31C4(b) requires the use of quick response sprinkler heads.

Although a “quick response” sprinkler head can activate at the same temperature as a “normal” sprinkler head, its reaction time is much shorter and it has different discharge characteristics. Therefore, S17C5 requires that the sprinkler system be designed specifically for the use of these heads.

(1) Where an atrium is separated from the remainder of the building by walls or doors incorporating glazing, a wall wetting system must be provided to protect the glazing as follows:

  1. On the atrium side of the glazing — to all glazed walls which are set back more than 3.5 m from the atrium well.
  2. On the atrium side of the glazing — to all glazed walls which are not set back, or are set back 3.5 m or less, from the atrium well, for all levels which are less than—
    1. 12 m above the floor of an atrium or the floor of the highest storey where the bounding wall is set back more than 3.5 m from the atrium well if a Class 2, 3, 5 or 9 part of the building is open to the atrium; or
    2. 20 m above the floor of an atrium or the floor of the highest storey where the bounding wall is set back more than 3.5 m from the atrium well if a Class 6, 7 or 8 part of the building is open to the atrium.
  3. On the side of the glazing away from the atrium well — to all glazing forming part of the bounding wall at each storey.

(2) Sprinklers must be located in positions allowing full wetting of the glazing surfaces without wetting adjacent sprinkler heads.

(3) Sprinkler heads must be of the quick response type and have a maximum temperature rating of 74°C.

(4) The rate of water discharge to protect glazing must be not less than—

  1. on the atrium side of the glazing—
    1. 0.25 L/s.m2 where glazing is not set back from the atrium well; or
    2. 0.167 L/s.m2 where glazing is set back from the atrium well; and
  2. on the side away from the atrium well — 0.167 L/s.m2.

(5) In addition to that of the basic sprinkler protection for the building, the water supply to required wall wetting systems must be of adequate capacity to accommodate the following on the atrium side of the glazing:

  1. Where the bounding walls are set back less than 3.5 m from the atrium well — wall wetting of a part not less than 6 m long for a height of not less than—
    1. 12 m above the floor of an atrium or the floor of the highest storey where the bounding wall is set back more than 3.5 m from the atrium well if a Class 2, 3, 5 or 9 part of the building is open to the atrium; or
    2. 20 m above the floor of an atrium or the floor of the highest storey where the bounding wall is set back more than 3.5 m from the atrium well if a Class 6, 7 or 8 part of the building is open to the atrium.
  2. Where the walls are set back 3.5 m or more from the atrium well — wetting of a part not less than 12 m long on one storey.

To set out fire protection requirements for glazed walls to an atrium.

S31C5(1) sets out the requirements for sprinkler protection of glazed bounding walls. These requirements are illustrated in Figure S31C10.

Under S31C5(2), the location of the sprinkler heads must allow full wetting of the glazing without wetting an adjacent head. Consequently, water should run down the window, cooling the glass and therefore creating a resistance to the spread of fire and/or smoke through the glazed wall by reducing its potential to failure during a fire. It is also important that the adjacent sprinkler head not be wetted, because the cooling effect of the water may delay its activation.

Because of the additional fire hazard associated with atriums, S31C5(3) requires the use of “quick response” sprinkler heads.

Although a “quick response” sprinkler head can activate at the same temperature as a “normal” sprinkler head, its reaction time is much shorter and it has different discharge characteristics.

S31C5(4) sets out the minimum requirements for water discharge rates. S17C5 therefore requires that the sprinkler system be designed specifically for the use of these heads.

S31C5(4) sets out the required water discharge rates on any glazing in a bounding wall. Because the atrium can have a high fire load and large volume, the higher flow rate of 0.25 L/s.m2 is required on the atrium side of the glazing when the wall is not set back from the atrium well.

The importance of the wall sprinklers to glazed walls in a fire is such that S31C5(5) sets out the minimum potential coverage to be provided by such sprinklers, which in turn determines the characteristics of the water supply in terms of pressure and quantity.

The water supply for the wall wetting system referred to in S31C5(5) is additional to the water supply for the other sprinklers in the building.

It is assumed that the size of a fire will be controlled by the sprinkler system installed in the building. The greater height required to be covered by a wall wetting sprinkler system in a Class 6, Class 7 or Class 8 part of a building (see S31C5(5)(a)(ii)) reflects the greater fire load contained in such buildings.

(1) Basic sprinkler and wall wetting systems protecting a building containing an atrium must be provided with easily accessible and identified stop valves.

(2) Sprinkler and wall wetting systems must be provided with independent stop valves.

(3) Sprinkler heads protecting the roof of the atrium must be provided with a stop valve.

(4) Stop valves to wall wetting and roof sprinklers may be of the gate type.

(5) All sprinkler and wall wetting stop valves must be monitored to detect unauthorised closure.

To set out requirements for sprinkler and wall wetting system stop valves.

When referring to sprinkler and wall wettingstop valves, S31C6requires that:

  • they be monitored to detect and warn of any unauthorised closure; and
  • the sprinklerand wall wettingsystems have independent valves.

Smoke control system

Except where varied or superseded by this Specification, mechanical air-handling systems in a building containing an atrium must comply with AS 1668.1.

To set out the general requirements for the installation of a suitable smoke control system in a building containing an atrium.

As generally required by the BCA, mechanical air-handling systems must comply with AS 1668.1. However, if any conflict exists between AS 1668.1 and Specification 31, the specification takes precedence.

Mechanical air-handling systems serving an atrium must be designed to operate so that during a fire—

  1. a tenable atmosphere is maintained in all paths of travel along balconies to required exits during the period of evacuation; and
  2. smoke exhaust fans serving the atrium are only activated when smoke enters the atrium; and
  3. central plant systems do not use the atrium as a return air path; and
  4. central plant systems which use return air paths remote from the atrium—
    1. cycle to the full outside air mode; and
    2. stop supply air to the fire affected storey or fire compartment; and
    3. continue to fully exhaust the fire affected storey or fire compartment and reduce the exhaust from other storeys or fire compartments by at least 75%; and
    4. continue to supply air to fire compartments or storeys other than the fire affected storey or fire compartment; and
  5. fans performing relief or exhaust duty from the atrium stop normal operation; and
  6. floor by floor, or unitary, air-handling plant serving a single fire compartment or storey—
    1. ceases normal operation in the fire affected storey or fire compartment; and
    2. commences full relief or exhaust from that fire affected storey or fire compartment; and
    3. continue to supply air to fire compartments or storeys other than the fire affected storey or fire compartment.

To set out mechanical air-handling system requirements for an atrium.

The basic operation of the mechanical air-handling system during a fire is to limit the spread of smoke. To achieve this it must:

  • maintain a tenable atmosphere along balconies to allow the occupants to evacuate; and
  • avoid smoke being drawn into the atrium when a fire occurs in another part of the building, which requires that—
    • the atrium smoke exhaust fans activate only when smoke enters the atrium;
    • the atrium cannot be used as a return air path; and
    • the normal relief or exhaust fans in the atrium must stop normal operation. If necessary, these fans may be designed for exhausting smoke from the atrium.

The intent of the details contained in S31C8(d) and (f) is to create a negative air pressure on the fire floor or in the fire affected compartment, so that air and any entrained smoke is drawn to it. This creates positive pressure on non-fire floors, so as to prevent the migration of smoke to non-fire floors while exhausting smoke from a fire affected floor.

(1) The smoke control system must be activated by—

  1. operation of an automatic fire alarm; or
  2. operation of the sprinkler system; or
  3. a manual start switch.

(2) All controls for the smoke control system must be located—

  1. in the fire control room; or
  2. in the emergency control centre (if any); or
  3. adjacent to the sprinkler control valves; or
  4. incorporated in the Fire Indicator Panel.

To set out how a smoke control system serving an atrium is to be activated.

The smoke control system may be activated by any of the methods listed in S31C9(1).

The location of the controls for the system may be any of those listed in S31C9(2). Note that the locations are in areas normally accessed and used by the fire brigade during a fire.

A smoke exhaust system serving an atrium must be designed on the basis of—

  1. the sprinkler system limiting the size of a fire to—
    1. a heat output of 1.5 MW and perimeter of 7.5 m if a Class 2, 3, 5 or 9 part of the building is open to the atrium; or
    2. a heat output of 5 MW and perimeter of 12 m if a Class 6, 7 or 8 part of the building is open to the atrium; and
  2. a smoke plume reaching a level 3 m above the highest storey having a path of travel to a required exit along a balcony bounding the atrium well, and not less than—
    1. 12 m above the floor of an atrium or the floor of the highest storey where the bounding wall is set back more than 3.5 m from the atrium well if a Class 2, 3, 5 or 9 part of the building is open to the atrium; or
    2. 20 m above the floor of an atrium or the floor of the highest storey where the bounding construction is set back more than 3.5 m from the atrium well if a Class 6, 7 or 8 part of the building is open to the atrium; and
  3. the smoke exhaust system discharging smoke at a rate of not less than that shown in Figure S31C10 for the appropriate height of smoke plume and fire size—
    1. from the top of the atrium; or
    2. horizontally, where calculations of wind velocity induced pressure profiles for the building verify that the exhaust system will operate effectively for all wind directions.
Figure S31C10 Smoke exhaust rate
image-S31C10-smoke-exhaust-rate.svg

To set out the design characteristics of a smoke exhaust system serving an atrium.

S31C10 specifies the characteristics on which a smoke exhaust system design must be based, which are:

  • the size to which the sprinkler system will limit a fire, in terms of its heat output and perimeter;
  • the extent of any smoke plume; and
  • the system’s discharge rate, as calculated under Figure S31C10 of the BCA.

Figure S31C10 of the BCA must be used to determine the minimum smoke extraction rate from the atrium. The required rate depends on the fire load specified in S31C10(a) and the height of the smoke plume above the floor of the atrium well specified in S31C10(b).

The exhaust rates are based on the need to maintain the smoke plume safely above any egress path.

 

Notwithstanding S31C10(c), the average upward air velocity in the atrium, due to the required smoke exhaust quantity must—

  1. be not less than 0.2 m/s at any level over an 18 m height above the floor of the atrium; and
  2. not exceed the following maximum velocities in atriums of constant cross sectional plan area:
    1. For occupancy classification qualifying for 1.5 MW fire size — 3.5 m/s.
    2. For occupancy classifications qualifying for 5 MW fire size — 5 m/s.

To enable the movement of smoke to the roof, for venting externally.

If the smoke is allowed to travel up the atrium due to its own buoyancy, in higher atriums it will reach a stage where it will not travel any higher. The reasons for this include:

  • the smoke will not have enough buoyancy to reach the top of the atrium; and
  • the smoke will entrain air, and cool as it rises.

Accordingly, to make sure the smoke continues to travel up the atrium well, minimum (see S31C11(a)) and maximum (see S31C11(b)) air velocities are specified. The maximum velocity specified in S31C11(b) only applies to an atrium well with a constant plan cross section.

(1) Smoke exhaust must be provided by fans capable of continuous and required operation for a period of not less than 1 hour when handling exhaust gases at 200°C.

(2) Where a Class 2, 3 or 9 part of a building adjoins an atrium, the atrium must be provided with a minimum of 3 fans each capable of 50% of the total required smoke exhaust capacity.

(3) Atriums other than those referred to in (2) must be provided with a minimum of 2 fans each capable of 50% of the total required smoke exhaust capacity.

To set out the operational requirements for exhaust fans.

To make sure that exhaust fans operate effectively during a fire, they must be designed to operate for at least 1 hour at a temperature of 200°C (see S31C12(1)).

Under S31C12(2) and (3), to make sure that at least one fan continues to operate during a fire:

  • at least three fans are required in atriums adjoined by Class 2, Class 3 or Class 9 parts, because of the heightened risk levels in such areas. This is due to such factors as the possibility that people will be sleeping and, in Class 9a buildings, the presence of non-ambulatory occupants; and
  • at least two exhaust fans are required in all other atriums.

 

Notwithstanding S31C12, automatic vents complying with AS 2665 may be used, except where a Class 6 part of a building adjoins the atrium, in lieu of exhaust fans provided that—

  1. the height from the atrium floor to the bottom of the highest vent is not more than 12 m; and
  2. the vents are fitted with a remote manual operation switch located adjacent to the sprinkler control valves or incorporated in the Fire Indicator Panel.

To set out requirements for smoke and heat vents, which are permitted in low-rise atriums.

Smoke and heat vents are permitted in low-rise atriums (i.e. atriums less than 12 metres high), instead of a mechanical smoke extraction system. The reason for the S31C13(a) limit is that 12 metres is considered to be a height to which smoke will travel due to its own buoyancy and still be effectively vented.

S31C13 does not apply where a Class 6 part of a building adjoins the atrium.

S31C13(b) requires that vents be fitted with a manual override switch, for use as necessary by emergency services personnel.

(1) Uniformly distributed make-up air must be provided to the atrium exhaust system from—

  1. outside the atrium at or near the lowest storey level; and
  2. relief air from non-fire storeys.

(2) A discharge volume sufficient to maintain a velocity of not less than 0.1 m/s towards the atrium well must be provided on all storeys where the bounding wall is set back from the atrium well.

(3) The requirements of (1)(a) are satisfied if make-up air is provided to the atrium exhaust system in such a manner as to prevent, as far as possible, disturbance of the smoke layer due to turbulence created by the incoming air, through—

  1. openings directly from the outside air to the atrium and located as close as practicable to the lowest level of the atrium; or
  2. ducts from the outside air to the atrium which deliver air as close as practicable to the lowest level of the atrium and, where passing through any other fire compartment having an FRL of at least 60/60/60; or
  3. a combination of (a) or (b).

To set out requirements for air flow into an atrium from which smoke-laden air is being extracted.

S31C7 to S31C13 require that smoke-laden air be exhausted from an atrium. S31C14 sets out how this exhausted air is to be made-up (i.e. replaced) in the atrium.

S31C14(1) is a performance criterion that requires make-up air to be provided from outside the atrium at a level at or near the lowest storey of the atrium and non-fire storeys.

To make sure that the area where the bounding walls are set back from the atrium well is kept smoke free, an air velocity of 0.1 m/s is required by S31C14(2). This velocity is consistent with that required through an open door by a fire-isolated stairway pressurisation system which accords with AS 1668.1.

S31C14(3) provides a means of achieving compliance with S31C14(1). It is important that the make-up air assists (and does not disturb) the exhausting of the smoke layer. To achieve this, the make-up air should enter the atrium at as low a level as possible, preferably at the base of the atrium. The make-up air must be provided from:

  • openings designed to open to outside air on detection of a fire in the atrium;
  • a system of ducts to supply outside air to the atrium; or
  • a combination of the above.

If a system of ducts is used to supply the make-up air, to make sure the system operates when needed during a fire the ducts must have an FRL of 60/60/60 if they pass through a different fire compartment to the atrium.

Fire detection and alarm system

Except where superseded by this Specification, automatic fire detection and alarm systems in a building containing an atrium must comply with AS 1670.1.

To set out the general requirements for the installation of a suitable fire detection and alarm system in a building containing an atrium.

A building’s fire detection and alarm system must, in general, comply with AS 1670.1. However, if any conflict exists between AS 1670.1 and Specification 31, the Specification takes precedence.

Smoke detection within an atrium—

  1. must be provided within all outside air intakes and at individual floor return air intakes of all air-handling systems to initiate automatic fire mode operation, and where applicable, comply with the restart facilities in AS 1668.1; and
  2. must operate at an obscuration level not greater than 0.5% per metre with compensation for external airborne contamination as necessary; and
  3. must sample air within the atrium and in storeys where the bounding wall is set back more than 3.5 m from the atrium well; and
  4. must be calibrated to compensate for smoke dilution where sampling occurs within return air path common to more than one room; and
  5. may incorporate beam type detectors to sense smoke in an atrium in a Class 5, 6, 7 or 8 building with an effective height of not more than 25 m if the beam detectors are—
    1. located at intervals of not more than 3 storeys; and
    2. arranged to scan at 90 degrees orientation to adjacent beam units.

To set out requirements for smoke detectors in an atrium.

S31C16 sets out, in detail, the requirements for smoke detectors within an atrium. The aim of these requirements is to make sure that the smoke detection system operates effectively and false alarms are minimised.

Smoke detection systems must be located at all return and relief air openings associated with the building air-handling systems and be—

  1. of the sampling type system as required in S31C16; or
  2. of the point type photoelectric smoke detector.

To set out requirements for smoke detectors at return and relief air openings.

S31C17 sets out the requirements for smoke detectors at return and relief air openings.

(1) A break-glass fire alarm point must be provided at each door to a fire-isolated stairway, fire-isolated ramp or fire-isolated passageway.

(2) A staged alarm must be provided where an air sampling type smoke detection system is provided for the atrium, and must operate as follows:

  1. Alert building management when abnormal smoke levels of 0.03% obscuration per metre are detected.
  2. Initiate a second alarm to management and start all smoke control systems including pressurisation of escape routes when smoke levels of 0.07% obscuration per metre are detected.
  3. Automatically call the fire brigade, activate the emergency warning and intercom system, and de-activate all plant not necessary for fire safety within the building when smoke levels of 0.09% obscuration per metre are detected.

(3) Beam and point type smoke detectors required must simultaneously operate all functions referred to above and activate at the level set out in AS 1670.1.

To set out requirements for alarm systems in a building containing an atrium.

Alarm systems required in a building containing an atrium, must include a manual call point (break-glass) alarm at each door to a fire-isolated exit. The aim of this provision is that a person is able to break the glass setting off the alarm as they evacuate the building, in advance of the automatic activation of the alarm system.

Where a sampling type smoke detection system is provided, a staged alarm must be given. The stages are set out in S31C18(2)(a) to (c). The reason for the staged alarms is to minimise the occurrence of false alarms.

Under S31C18(3), beam and point type smoke detectors (as with a sampling type smoke detection system) must also operate as set out in S31C18(2)(a) to (c), but at the levels set in AS/NZS 1670.1. This provision only applies to beam and point type smoke detectors required by the BCA.

Additional requirements

A building containing an atrium must be provided with an emergency warning and intercom system which—

  1. complies with AS 1670.4; and
  2. incorporates visual warning devices that—
    1. operate upon the evacuation signal; and
    2. display the word “EVACUATE” in red with letters conforming with the requirements of the Deemed-to-Satisfy Provisions of Part E4 for exit signs.

To require that a suitable emergency warning and intercom system is installed in a building containing an atrium.

S31C19 requires the installation of an emergency warning and intercom system in any building containing an atrium. The system must comply with:

  • AS 1670.4; and
  • the additional requirements set out in S31C19(b).

The system is a combination of an emergency warning system and an emergency intercom. The main function of an integrated system is:

  • to generate an alert and evacuation signal;
  • to facilitate communication with evacuation zones; and
  • to provide communication between the building management or emergency services personnel and strategic points within the building.

The operation of the system may be by a number of measures referred to in Specification 31, including the manual call point (break- glass) alarm required by S31C18(1).

(1) If a required path of travel to an exit is within an atrium, a suitable alternative power supply must be provided to operate required safety systems, including sprinkler systems and fire hydrant pumps, air handling systems, alarms, warning and communication systems and emergency lighting circuits.

(2) The alternative power supply must—

  1. be connected automatically if the normal power supply fails; and
  2. if located within the building, be separated from the remainder of the building by an enclosure with an FRL of at least 120/120/120; and
  3. be connected to the safety systems by means of cabling complying with C3D14(3).

(3) The requirements of (1) are satisfied by—

  1. a single medium voltage supply taken from an electricity substation situated within, or adjacent to, the building concerned where the power supply to the substation consists of two or more high voltage cables each taking electricity from separate transformers; or
  2. two or more medium voltage supplies each taking electricity from separate electricity substations situated—
    1. outside the building concerned; and
    2. at a suitable distance from each other; or
  3. a single medium voltage supply taken from an electricity substation together with an electricity generating plant capable of—
    1. generating a medium voltage supply; and
    2. starting and taking the required electrical load within a period of not more than 30 seconds from the time of normal supply failure.

To require the installation of a suitable standby power system in a building containing an atrium.

S31C20 only applies where a required path of travel to an exit passes through an atrium (see S31C20(1)).

Under S31C20(1), because of the need to continue the operation of emergency services, a standby power supply is required. This is particularly important because of the increased fire hazard associated with atriums, and the dangers for occupants if they have to evacuate through atriums.

To make sure it operates when needed during a fire, the standby power supply must:

  • automatically come into operation when the normal power supply fails;
  • if located within the building, be protected by fire-resisting construction;
  • be connected to the safety systems by means of cabling suitable to resist fire; and
  • come from two supply sources.

S31C20 is consistent with the protection required for electricity supply systems in C3D14.

S31C20(3) sets out means of achieving compliance with S31C20(1). To make sure that the necessary power to operate the emergency equipment is available during a fire, it requires the standby power to be from one of the listed alternatives.

Required fire-isolated exits in a building containing an atrium must be protected from the entry of smoke in accordance with E2D3.

To minimise the risk of smoke entering a fire-isolated exit in a building containing an atrium.

Reference to E2D3, and in particular E2D4 to E2D13, means that all fire-isolated exits serving an atrium must be provided with a pressurisation system in accordance with AS 1668.1. The reason for this is the additional fire hazard associated with atriums and for occupants evacuating them.