NOTE General recommendations applying to all building types are given in

Section 4 to Section 9. This annex gives additional recommendations that are specific to atria. Buildings containing atria need to meet both the general recommendations in Section 4 to Section 9, and the specific recommendations given in this annex.

COMMENTARY ON ANNEX B

General

a) Risk of Fire Spread: Atriums can accelerate the spread of smoke and fire between storeys due to the increased volume of smoke and air entrainment.

b) Design Principles for Atriums:

· Escape Route Planning: Design effective escape routes from areas at risk.

· Fire Development Limitation: Use controlled materials and automatic suppression systems.

· Fire Warning Systems: Implement fire detection and alarm systems.

· Atrium Separation: Physically separate the atrium from other areas.

· Smoke and Temperature Control: Install systems to manage smoke, pressure, and temperature.

· Management Control: Ensure effective fire safety management.

c) Smoke and Fire Spread:

· Buoyancy of Smoke: Smoke rises and expands in the atrium, leading to large volumes of smoke on upper storeys.

· Enclosure Effects: Fire-resisting enclosures reduce smoke spread, but may fail if the fire is large.

d) Fire-Fighting:

· Smoke Clearance: Provide smoke control measures to assist fire services, but these are not suitable for protecting escape routes.

e) Considerations:

· Atrium Design: The recommendations might not be suitable for all buildings; consult Annex C for design solutions and examples.

· Enclosure Materials: Use fire-resisting materials to improve protection.

The design of atriums requires specific strategies to manage fire and smoke effectively, ensuring both safety and functionality.

B.1 General

a) Documentation:

Designs based on calculations should be documented, including detailed calculations, assumptions, and input parameters.

a) Application of Principles:

Apply the principles to buildings with atria as recommended in 31.3.1.1, except:

· Occupancy Types C1 or C2: Follow BS 9991.

· Confinement Buildings: Prisons or similar.

· Entertainment Venues: Auditoria in theatres or similar.

· Shopping malls: Malls in shopping complexes.

· Small Premises: Small buildings.

· Two-Storey Atriums: Buildings with two-storey atriums where one storey is at ground level, designed for simultaneous evacuation with exits remote from the atrium.

b) Additional Standards: In cases not specifically covered, apply the standards for equivalent non-atrium buildings.

B.2 Occupancy and building characteristics

B.2.1 General

Considerations for Fire Safety Strategy:

Building Occupancy Type
Degree of Separation: Between atrium and associated floor areas
Size and Geometry: Of the atrium
Atrium Use and Fire Load Control: At the atrium base
Building-Site Relationship: Proximity to site boundaries
Building Height

B.2.2 Building in different occupation

Occupancy Types: Different types within the building
Associated Fire Safety Measures: For each occupancy category
Cross-Category Checks: Ensure measures for one category don’t negatively impact others

B.2.3 Glazing elements

COMMENTARY ON B.2.3

a) Smoke Temperature ≤ 200°C:

Laminated or toughened glass suitable for smoke-retarding, if no fire/flame exposure risk.

b) Higher Smoke Temperatures:

Use classified fire-resisting glazed systems (BS EN 1364-1) or assemblies conforming to BS EN 12101-1.

B.2.4 Connection of atrium to below-ground storeys

COMMENTARY ON B.2.4

a) Fire and Smoke Spread:

Little difference from above-ground atriums.

b) Separation:

No need for fire-resisting construction between below-ground and upper storeys.

c) Recommendations:

Ensure protected escape routes and fire-fighting provisions follow standards for non-atrium buildings.

B.2.5 Use of atrium base

NOTE Detailed recommendations regarding the control of fire loading on the atrium base are given in B.7.

Sprinkler Protection: Often impractical for combustibles on atrium base.
Control Fire Load: Limit combustible materials to isolated islands.
Automatic Suppression: If effective, assume fire load is controlled.

B.3 Means of escape

B.3.1 General

a) Purpose:

Active and passive fire and smoke control systems in an atrium ensure means of escape remain available during evacuation.

b) Guidance:

Follow established guidance for means of escape, unless specifically stated otherwise in this annex.

B.3.2 Balcony escape

COMMENTARY ON B.3.2

a) Balcony Escape Routes: Acceptable if protected from heat and smoke; alternative routes not needed if available.

b) Requirements:

· Sprinklers: Install throughout the building, unless exempt by smoke control design.

· Escape Routes: Two directions required, with travel distance to nearest storey exit ≤ 18 m.

· Enclosed Balconies: Provide temperature control if not fire-resisting.

· Open Balconies: Implement smoke and heat exhaust to maintain smoke layer ≥ 3 m above balcony.

· Construction: Enclosed balconies should have fire-resisting and smoke-retarding construction.

· Fire Load: Control on the atrium base.

B.3.3 Evacuation procedures

a) Evacuation Types:

· Simultaneous Evacuation:

Recommended when:

· There are open connections between storeys or non-smoke-retarding enclosures in the atrium.

· Occupants are unlikely to remain safely on an open storey due to psychological reactions to fire threats.

· Phased Evacuation:

Suitable when:

· High-rise buildings have smoke-retarding and fire-resisting enclosures separating floor areas from the atrium.

· Low-rise buildings have smoke-retarding but non-fire-resisting enclosures.

b) Factors to Consider:

· Mode of evacuation (phased, simultaneous, or both).

· Nature of the occupants.

· Fire risk present in the building.

NOTE 1 The appropriate degree of fire resistance is shown in the relevant decision tree in Annex C.

NOTE 2 Recommendations for simultaneous and phased evacuation are given in 12.2.

B.3.4 Fire control centres

a) Assessment Criteria:

Evaluate the complexity of the building.
Consider the associated building management systems.

b) Fire Control Center Requirement:

Atrium Buildings with Phased Evacuation:

A fire control center must be provided to allow the fire and rescue service to take immediate control upon arrival.

NOTE Most atrium buildings are likely to contain some fire safety systems that might not be needed in an equivalent non-atrium building.

B.4 Separation between the atrium and the associated floor area

B.4.1 General

a) Construction Requirements:

Separation: The construction separating the atrium from associated floor areas should be fire-resisting and/or smoke-retarding.

b) Fire Load Assessment:

Consider both the atrium base and the associated floor area when determining the fire load.

B.4.2 Fire- resisting construction

a) Fire-Resisting Construction:

The separation between accommodation and the atrium must meet the integrity criterion:
- BS 476-22: Minimum of 30 minutes.
- BS EN 13501: Equivalent classification.
Follow other recommendations if specified elsewhere.

B.4.3 Smoke- retarding construction

COMMENTARY ON B.4.3

a) Smoke-Retarding Enclosures:

· Purpose: Prevent early smoke ingress to unaffected levels.

· Glass Systems: Framed or butt-jointed glazed constructions with sealants are considered smoke-retarding.

· Smoke Curtains: Must conform to BS EN 12101-1.

· Joints and Seals: Must be tight, sealed with appropriate materials (e.g., plaster, mastic, flexible strips), and conform to BS EN 1366-3 or BS EN 1366-4.

b) Doors in Atriums:

· Testing: Should meet leakage rate standards when tested per BS 476-31.1 or BS EN 1634-3 and classified per BS EN 13501-2. Leakage rate must not exceed 3 m³/h per meter.

c) Fire Separation Function:

· Glazed Construction: If required to resist fire, it should be fire-resisting for integrity or insulation as needed.

d) Usage of Smoke-Retarding Construction:

· Only used when smoke temperatures are controlled by sprinklers and/or temperature control systems.

B.4.4 Glazing

NOTE 1 Overhead (roof) glazing needs to be designed to minimize the risk of injury due to falling glass during normal use of the atrium. This generally requires the use of polyvinyl butyral (pvb) laminated safety glass on the inner pane facing into the atrium space, in accordance with the recommendations in BS 5516-2.

Glazed atrium walls and the atrium roof should meet the following recommendations.

NOTE 2 The design solutions and exemplars in Annex C can be used to determine the necessary fire resistance for vertical glazing of the atrium walls according to the risk profile and atrium height.

a) Vertical Glazing Requirements:

Location:

Either side of the corner where the atrium forms a vertical escape and access stair.

Distance:

At least 3 meters on both sides of the corner.

Performance:

Minimum 30 minutes of insulation and integrity for the full height of the atrium.

NOTE 3 Higher performance classifications might be possible subject to risk profile; see Annex C.

a) General Requirement:

- Fire-Resisting Glazing: Should be a fire-resisting glazed system with a minimum of 30 minutes integrity performance.
- Testing/Classification: Tested in accordance with BS 476-22 or classified per BS EN 13501-2.

b) Exceptions with Fire Safety Measures:

- Sprinkler System or Fire-Resisting Separation: If a sprinkler system (BS EN 12845) is provided, or if there is a fire-resisting separation with a minimum of 60 minutes fire resistance, and fire load is controlled:
- - Thermally Toughened Glass: Must meet integrity criteria for at least 60 minutes (BS 476-22 or classified E60 per BS EN 13501-2).
  - Laminated Safety Glass: Must conform to BS EN ISO 12543-2 with temperature control of hot smoke to a maximum of 200°C, and no risk of direct flame impingement.

c) Temperature Control:

- Control System or Smoke-Retarding Construction: Necessary to limit the temperature of hot gases and smoke or prevent significant hot smoke contact with the roof glazing.

d) No Temperature Control or Smoke-Retarding Construction:

- Fire-Resisting Glazing: If neither temperature control nor smoke-retarding construction is used, roof glazing should meet the fire-resisting criteria for a minimum of 30 minutes integrity as per B.4.4b).

NOTE 4 Higher performance classifications might be possible subject to risk profile; see Annex C.

Glazing Requirements:
- Fire-Resisting System: Façade glazing outside and above the atrium must be part of a fire-resisting glazed system.
- Coverage: Extends for at least two floors above the atrium roof.

Performance Classification:
- Integrity Only: Minimum 30 minutes integrity for risk profiles A1, A2, A3, B1, and B2.
- Integrity and Insulation: Minimum 30 minutes integrity and insulation for risk profiles B3, C1, C2, and C3.

NOTE 5 For risk profiles A4, B4 and C4, see 6.4 and Table 4.

B.5 Smoke and heat control systems

COMMENTARY ON B.5

a) Types of Smoke Control Systems:

· Smoke and Heat Exhaust Ventilation:

· Stable Smoke Layer: Provides clear air for safe escape.

· Smoke Dilution: Maintains tenable conditions by diluting smoke.

· Smoke Clearance System:

· Assists firefighters in removing smoke after a fire.

· Temperature Control System:

· Reduces fire gas temperatures in the atrium to allow non-fire-resisting materials in the atrium façade.

· Pressure Differential System:

· Atrium Pressurization: Pressurizes the atrium relative to accommodation to prevent smoke ingress if no significant fire-load and fire-resisting separation.

· Pressurization of Associated Floor Areas: Pressurizes adjacent spaces relative to the atrium if there is a controlled fire load and no smoke and heat exhaust.

· Atrium Depressurization: Reduces atrium pressure to prevent smoke entry into adjacent spaces if there is a controlled fire load and smoke and heat exhaust ventilation.

b) HVAC Ductwork Considerations:

· Risk of spreading smoke and fire.

· Requires careful fire protection, integrity, and routing to ensure effective smoke control.

B.5.1 Calculation procedures

NOTE Guidance on calculation procedures for the design of smoke and heat control systems can be found in a number of documents, e.g. BS 7346, BR 368 [N3], BR 258 [90] and CIBSE Guide E [46].

Designers should establish that the calculation procedures used are relevant to the circumstances in which they are intended to be used. The procedures and calculations, together with any assumptions, should be fully documented.

B.5.2 Smoke and heat exhaust ventilation systems

a) Clear Layer:

· Maintain a clear layer of at least 3 meters above the topmost open occupied storey or 2.5 meters above the floor of fire origin.

b) Temperature Control:

· Ensure the smoke layer temperature does not exceed 200°C.

c) Smoke Leakage and Visibility:

· Prevent smoke from leaking into closed storeys.

· Ensure smoke optical density does not exceed 0.1% per meter on the topmost open storey to maintain visibility of 8 to 10 meters for safe use of escape routes.

B.5.3 Temperature control systems

a) Material Identification:

· Identify materials on the atrium façade with the lowest critical temperature for failure.

· Ensure that failure of these materials does not breach the integrity of the atrium façade.

b) Compliance:

· Adhere to recommendations for the behaviour of different types of glazing as specified in B.4.4.

NOTE It is possible, by careful design, to combine a temperature control system of this type with a smoke and heat exhaust ventilation system meeting the recommendations of B.5.2 (for example, so that storeys below the design layer base can be open to the atrium).

B.5.4 Pressure differential system

a) Sprinkler System Requirement: Buildings should have a sprinkler system:

· New Systems: Designed and installed as per BS EN 12845.

· Existing Systems: Designed and installed as per BS 5306-2.

i) Exceptions to Sprinkler Requirement:

· Atrium height is less than 30 meters.

· Atrium is separated from associated areas by fire-resisting construction.

· A pressure differential system protects associated areas from smoke in the atrium.

· Fire safety engineering design solutions do not necessitate sprinklers.

NOTE 1 This recommendation applies to atrium pressurization, atrium depressurization and pressurization of associated floor areas.

b) Neutral Pressure Plane Assessment:

· When the atrium might contain smoke and adjacent areas (e.g., accommodation storeys, stairwells, shafts) need pressurization.

· Calculate the height of the neutral pressure plane in the atrium, considering normal building leakage (refer to BS 7346-4).

NOTE 2 This recommendation applies to atrium pressurization, atrium depressurization and pressurization of associated floor areas.

c) Minimum Design Pressure Difference:

· Up to 10 m above Neutral Pressure Plane: 50 Pa across closed doors or other leakage paths.

· Between 10 m and 25 m above Neutral Pressure Plane: 75 Pa across closed doors or other leakage paths.

d) Smoke-Retarding Construction Requirement:

· Any part of the enclosure separating the atrium from associated storey areas located more than 25 m above the neutral pressure plane must:

· Be of smoke-retarding construction.

· Have at least 30 minutes of fire resistance, regardless of other requirements.

NOTE 3 The two recommendations c) and d) apply to pressurization of associated floor areas.

e) Atrium Pressurization to Prevent Smoke Ingress:

Follow BS EN 12101-6:2005 guidelines as if the atrium were a pressurized stairwell.
Atrium Requirements:
- No combustible content in the atrium.
- Adjacent spaces must be separated from the atrium by fire-resisting construction.

NOTE 4 This recommendation applies to atrium pressurization.

f) Smoke and Heat Exhaust to Reduce Atrium Pressure:

· Aim to raise the neutral pressure plane above the highest vulnerable leakage path in the atrium containing thermally-buoyant smoky gases.

· Consider external wind pressures explicitly in the design calculations.

NOTE 5 This recommendation applies to atrium pressurization and atrium depressurization.

B.6 Fire detection and fire alarm and warning systems

a) Voice Alarm System Requirement:

Required in atrium buildings where:
- Significant numbers of the public are likely to be present.
- Phased evacuation is adopted.
Must comply with BS 5839-8:2013.
Provide warnings in alternative formats.

NOTE 1 Fire alarms in most smaller atrium buildings are best operated in a “single stage” mode in which the actuation of a call point or detector gives an instantaneous warning from all fire alarm sounders for an immediate evacuation.

b) Automatic Fire Detection and Alarm System:

Necessary to prevent smoke from unoccupied areas spreading through the atrium and hindering escape from other levels.
Install a system in accordance with BS 5839-1:2013.
Category L2 standard unless specified otherwise.

NOTE 2 See BS 5389-1:2013, 22.9 and Table 3 for limits of ceiling height.

NOTE 3 Recommendations for public address/voice alarm systems are given in 15.3.

B.7 Controlling fire on the atrium base

COMMENTARY ON B.7

a) Fire Load Control on Atrium Base:

Objective: Limit the fire's heat output to 2.5 MW convective heat flux.
Achieved by:
- Controlling the combustible content, or
- Providing sprinkler protection to the atrium base.

B.7.1 General

a) Wall and Ceiling Linings:

· Must have at least a Class 1 surface spread of flame (BS 476-7) or be classified as C-s3, d2 (BS EN 13501-1:2007+A1).

b) Upholstered Furniture:

· Must resist ignition by both smouldering (ignition source 0) and flaming sources (ignition source 5) as per BS 5852:2006.

NOTE 1 Attention is drawn to the provisions of the Furniture and Furnishings (Fire) (Safety) Regulations 1988[91] in respect of filling materials.

c) Textiles (Drapes and Curtains):

· Must meet the requirements of BS 5867-2:2008.

NOTE 2 For further guidance see BS 5852:2006, BS 7176, BS EN 1021-1 and BS EN 1021-2.

B.7.2 Limitation of combustible content on atrium base

a) Limiting Combustible Content:

· Option A: Total weight of combustibles on the atrium base should not exceed 160 kg.

· Option B: If the weight exceeds 160 kg, materials should be confined to isolated islands, with each island:

· Containing a maximum of 160 kg of combustible material.

· Covering a maximum floor area of 10 m².

· Being separated from other combustible areas by at least 4 m, unless protected by a sprinkler system.

B.7.3 Provision of sprinkler protection to atrium base

Sprinkler System Design and Installation:
- New Systems: Must comply with BS EN 12845.
- Existing Systems: Must comply with BS 5306-2.

Effectiveness Consideration:
- Sprinkler effectiveness reduces with increased height above the atrium base.
- Design and installation must account for this to ensure effective control of the design-sized fire at the specific sprinkler height.

B.8 Restricting the spread of fire to adjacent sites

a) Space Separation in Atrium Buildings:

Relevant in unsprinklered atrium buildings.
Calculation of space separation should assume:
- All storeys not separated from the atrium by fire-resisting construction could be involved in the fire.
- Fire-resisting construction must meet the integrity criteria equivalent to atrium enclosure recommendations (B.4.2).

NOTE If an atrium building is sprinklered, the area of fire involvement is likely to be reduced to such an extent that the potential for fire spread to adjacent buildings can be regarded as being comparable to that of an equivalent non-atrium building that is compartmented at each level and protected by a sprinkler system.

B.9 Smoke clearance for fire- fighting

B.9.1 General

a) Post-Fire Smoke and Heat Release:

· Necessary for smoke and heat to be released after fire suppression.

· Ventilation typically achieved by opening windows for cross-ventilation and smoke clearance.

b) Atrium Building Challenges:

· Smoke spread across multiple storeys complicates window opening.

· A mechanical or natural ventilating system should clear smoke from the atrium and affected floors.

c) Smoke Control Systems:

· If a smoke control system for escape is present, additional facilities for fire services are generally unnecessary.

· Without such a system, smoke clearance facilities for fire service use are required.

d) Manual Override Facilities:

· Stand-alone manual override controls should be provided for the fire service to directly control smoke control and ventilation systems.

B.9.2 Atria not exceeding 30m in height

a) Natural Exhaust Vents in Atrium:

Vents should comply with BS EN 12101-2.
Vents must be located in the atrium roof.

Vent Area Requirements:

- Total geometric free area should be at least 10% of the maximum plan area of the void at the top floor level.
- Minimum vent area should be 1.5 m².

B.9.3 Atria of any height

a) Mechanical Smoke Ventilation in Atrium:

System must provide replacement air changes per hour based on the total atrium volume, including the largest open floor.

Air Change Requirements:
- Sprinklered buildings with controlled fire load: 4 air changes per hour.
- Unsprinklered buildings: 6 air changes per hour.
Fans should comply with BS EN 12101-3.

B.9.4 Ventilation and smoke controls for the fire and rescue service

a) Assisting Fire and Rescue Service:

Switches should be provided at appropriate locations.
Allows fire and rescue service or authorized personnel to:
- Override smoke and heat exhaust fans and ventilators.
- Alter the configuration of the normal air handling system.
- Aids in rescue, fire-fighting, and smoke clearance after fire extinguisher.

Annex B (normative) Recommendations for atria