Smoke Hazard Management: NCC Part E2 Overview

1. What This Covers and Why It Matters

Smoke kills more people in building fires than flames do. Most fire deaths come from breathing toxic gases before the fire reaches the occupant. NCC Part E2 addresses this directly. It sets out what every building needs to warn occupants, control smoke spread, and keep evacuation routes clear long enough for people to get out.

Part E2 contains two performance requirements. E2P1 requires automatic smoke warning systems in buildings where people sleep (Class 2, 3, 9a, 9c, and Class 4 parts). E2P2 requires that evacuation routes maintain safe temperatures, adequate visibility, and non-toxic air during the evacuation period. These apply to all building classes except open-deck carparks and open spectator stands.

2. DtS Provisions: What Each Building Class Needs

The DtS pathway organises smoke management around two variables: building class and effective height. The 25-metre effective height threshold is the main dividing line.

Buildings Over 25m Effective Height

Buildings 25m or Under

For Class 5, 6, 7b, 8, and 9b buildings with a rise in storeys greater than 2 (or greater than 3 for schools), clause E2D9 gives four options:

1. Automatic air pressurisation in fire-isolated exits (AS 1668.1)
2. Zone pressurisation between vertically separated compartments
3. Automatic smoke detection and alarm (Specification 20)
4. Sprinkler system (Specification 17, excluding FPAA101D/H types)

For healthcare buildings (Class 9a, 9c) at 25m or under, E2D11 requires smoke detection throughout, automatic HVAC shutdown on detection, and either zone pressurisation or sprinklers with residential heads if the rise in storeys exceeds 2.

Large Isolated Buildings (E2D10)

Buildings with floor area over 18,000 m² or volume over 108,000 m³ trigger additional requirements:

• Ceiling height 12m or under: automatic smoke exhaust (Specification 21) OR smoke-and-heat vents (Specification 22)
• Ceiling height over 12m: automatic smoke exhaust only (Specification 21)

Buildings at or under 18,000 m² floor area and 108,000 m³ volume still need one of: sprinklers, fire detection, smoke exhaust, smoke-and-heat vents, or natural venting.

3. Fire-Isolated Exits and Air Pressurisation

Clause E2D4 requires automatic air pressurisation for fire-isolated exits serving any of the following:

• Storeys above 25m effective height
• More than 2 below-ground storeys
• Atriums (Part G3 applies)
• Class 9a or 9c buildings with a rise in storeys greater than 2
• Class 3 residential care buildings with a rise in storeys greater than 2
• Fire-isolated passages or ramps with travel distance exceeding 60m to a road or open space

The pressurisation system creates a positive pressure differential that stops smoke from entering the stair or passage. AS 1668.1 sets out the design and commissioning requirements for these systems.

4. Smoke Exhaust Systems: Specification 21 in Detail

When the DtS path calls for mechanical smoke exhaust, Specification 21 sets the design parameters.

Design Fire Sizes

The exhaust system must handle smoke from these design fire sizes:

The system must keep the smoke layer not less than 2m above the highest floor level in the affected zone.

Smoke Reservoirs

Each smoke reservoir must not exceed 2,000 m² in horizontal area. Enclosed walkways and malls must not exceed 60m in length within a single reservoir. The reservoir needs a minimum depth of 500mm below an imperforate ceiling or roof. For multi-storey situations, add 400mm to the bulkhead or baffle depth.

All reservoir construction must use non-combustible, non-shatterable materials.

Fan Requirements

Smoke exhaust fans must operate continuously at 200°C for at least 1 hour. In unsprinklered buildings, fans must also handle 300°C for at least 30 minutes. Every fan must deliver the required volumetric flow rate at ambient temperature for early-stage response and commissioning testing.

Air Velocities

• Fan discharge: not less than 5 m/s
• Discharge point: minimum 6m from any air intake or exit
• Make-up air through doorways: must not exceed 2.5 m/s
• Multi-storey void make-up air: average 1 m/s across vertical openings to the fire-affected floor

Activation and Control

Smoke detectors activate exhaust fans sequentially. The detector zones must match the smoke reservoirs served by each fan group. When the smoke system activates, all non-smoke HVAC systems shut down automatically. A manual override must sit adjacent to the fire indicator panel (AS 1668.1 clauses 4.11 and 4.13). Theatres require an additional manual control at the stage manager's location.

5. Zone Pressurisation: How It Works

Zone pressurisation controls smoke by creating pressure differences between fire compartments stacked vertically. Exhaust fans run in the fire-affected zone while make-up air feeds the zones above and below. The pressure differential stops smoke from migrating through gaps in floors, service penetrations, and lift shafts.

Three important points about zone pressurisation under the NCC:

1. It applies only between vertically separated fire compartments - not horizontal compartments on the same storey
2. For buildings other than healthcare, the DtS provisions allow substitution with stairway pressurisation, smoke detection, or sprinkler protection
3. AS 1668.1 defines six methods of smoke control and sets out the design, construction, installation, and commissioning requirements for each

The 2015 revision of AS 1668.1 added a Hot Layer smoke control section (previously in AS 1668.3) and introduced mandatory Baseline Data requirements. The baseline data package must include design information, operating instructions, smoke control schematics, commissioning data, test results, and fire and smoke damper schedules.

6. What Developers Should Do With This

Start smoke hazard management planning at the concept stage. Here is the sequence:

1. Confirm building classification and effective height. These two variables determine the baseline DtS requirements. A 26m Class 5 building triggers zone pressurisation (E2D6). A 24m Class 5 building with 3 storeys triggers one of 4 options (E2D9).
2. Check for large floor areas. Any Class 6 fire compartment over 2,000 m² triggers additional requirements (E2D14-E2D15). Any building over 18,000 m² floor area or 108,000 m³ volume triggers E2D10.
3. Reserve space for smoke control plant. Smoke exhaust fans, pressurisation fans, shafts, and smoke reservoirs all need physical space. Smoke reservoir depths of 500mm minimum (plus 400mm for multi-storey) affect ceiling heights and floor-to-floor dimensions.
4. Coordinate with mechanical design early. Every HVAC system in the building must either operate per AS 1668.1 or include smoke dampers with automatic shutdown (E2D3). This affects duct routing, damper locations, and control wiring throughout the building.
5. Budget for ongoing compliance. Smoke control systems are essential safety measures under building legislation. Annual essential safety measure reports, routine testing, and maintenance records are ongoing obligations that transfer to the building owner at practical completion.