Smoke Ventilation Process: Enhancing Fire Safety in Buildings

Understanding Smoke Spread in Buildings

When materials burn in an enclosed building, they produce smoke which consists of gases, vapours and solid particles suspended in air. Smoke spreads rapidly upwards, across ceilings and horizontally through open doors and corridors due to temperature differences produced by the fire. Untreated smoke contains toxic gases like carbon monoxide, which can overcome people in very high concentrations within a few breaths. It also reduces visibility greatly, disorienting occupants. Smoke may spread up to 40 times faster than a person can walk. Within 3-5 minutes of ignition, smoke can fill an entire multi-storey car park or large warehouse and within 10 minutes, it will blanket all floors of an average office block. The density and toxicity of smoke depend on factors like type of fuel, ventilation and temperature of the fire.

Being aware of how fast smoke spreads helps firefighters determine ventilation requirements and positions needed to extract it. Modern building designs incorporate automatic vents and compartments to temporarily contain smoke spread for exit routes to remain usable longer during evacuation. For existing buildings, smoke ventilation strategies form a key part of firefighting response plans to maintain tenable zones for rescue teams.

Mechanisms of Smoke Ventilation

There are three main mechanisms used for smoke ventilation during building fires:

• Natural Ventilation: It uses temperature differences caused by the hot gases of the fire rising to draw smoke up and out through strategically located openings in the structure such as windows, skylights or wall/roof vents. These passive openings are actuated manually during firefighting operations to direct smoke movement.

• Mechanical Ventilation: Powered fans or ducting systems are employed to actively extract smoke at high rates from targeted areas. Large centrifugal smoke extract fans housed on the roof are commonly used to ventilate large open spaces like atriums or multi-storey car parks. In-situ fans may also pull smoke from compartment openings.

• Pressurisation: Clean air is pumped into parts of the building at lower pressure to prevent smoke ingress utilising fan systems. Stairwells are pressurised so that they remain tenable for evacuation routes. Compartments housing critical equipment like control rooms are also pressurised.

Combining different mechanisms based on the building design optimises smoke clearance. Positioning of vents and fans needs careful planning with inputs from computational fluid dynamics (CFD) modelling to effectively redirect smoke as desired.

Advancing Smoke Venting Technologies

There is active research to advance smoke ventilation technologies for enhanced building fire safety:

• Intelligent Smoke Vent Control: Using networked sensors to autonomously trigger different vents and fans based on sensed smoke/toxic gas levels at multiple locations within a building for more coordinated smoke management.

• Self-opening Vents: Vents that automatically open at preset temperatures to avoid delay from manual activation. Some use frangible disks or fusible links integrated directly into vent designs.

• Wireless Sensors: Wireless sensors installed across structures enable real-time tracking of smoke spread and early warning for evacuation. Their data feeds control algorithms for ventilation optimisation.

• Drones: Experimentation with drones equipped with sensors, cameras and small fans is underway. They can potentially navigate smoke layers conducting on-site air sampling and ventilation in hard to reach zones.

• Filtered Smoke Extractors: Filters attached to smoke extract outlets can remove particulate matter and toxic gases from exhaust air before release, minimising environmental impact and health risks to neighbouring areas.

Greater adoption of such technologies especially for high-risk buildings like tall towers, transport hubs and facilities housing flammable materials helps in expediting smoke clearance for life safety. Regulatory bodies are progressively incorporating their recommended use into fire codes and standards across regions.

Planning Smoke Ventilation for London Buildings

Effective smoke ventilation requires meticulous planning customised for each building. Some key aspects to consider for structures located in London and surrounding areas are:

• Structural Design: Incorporate minimum fire compartmentation and zoned smoke areas while maintaining adequate egress space around all openings in accordance with established building regulations.

• Location of Vents: Strategically situate smoke vents on lower floors, above compartmentation to direct smoke upwards and away from escape routes. Roof vents aid clearing atrium spaces.

• Fan Requirements: Size smoke extract fans to maintain prescribed minimum air changes for areas based on their use and occupancy. Ensure backup power arrangements.

• Control Panel: Centralised control of mechanical and natural vents with visual status connected to fire alarm system optimises coordinated operation by responders.

• Modelling Studies: Use CFD studies to determine impact of thermal plumes from realistic localised fires of different sizes on smoke propagation. Obtain certification.

• Wayfinding: Equip staircases, corridors with emergency signage illuminated through backup power guiding occupants to fire-rated assemblies under smoke-filled conditions.

• Maintenance: Regular inspection, testing and maintenance of all active and passive systems as per stipulated schedules ensures reliability during emergencies. Dedicated qualified staff help prepare detailed plans for each building.

• Coordination with Fire Services: Consult London Fire Brigade in planning and inspection process to understand firefighting techniques and strategies for the given site. Their expertise aids devising suitable solutions.

Adhering to approved designs while retrofitting existing structures and ensuring compliance of new buildings enhances protection for citizens and property in London from the spread of dangerous smoke in fires.

Case Studies of Effective Smoke Ventilation Systems

Two actual installations in London showcase judicious smoke ventilation design contributing to positive outcomes during real building fires:

• Heathrow Airport Terminal 5 - This massive passenger terminal utilises a combination of roof-mounted centrifugal smoke extract fans and automatic sidewall vents. In a kitchen fire, sensors rapidly activated vents directing smoke up into an atrium where fans efficiently extracted it outdoors within 13 minutes, preventing spread. No evacuations were needed. Post-fire analysis validated the design.

• Shard Skyscraper - Standing over 300 metres tall, Europe's tallest building relies on strategically placed mechanical vents connected to ducting which draws smoke directly to the top via stack effect during a fire. A rubbish chute fire caused smoke to rise as designed without spreading floors, allowing firefighters ready access for containment and crews to continue working in lower levels. CFD studies aided duct sizing and vent placement.

Such successful applications illustrate how carefully engineering smoke ventilation according to fire dynamics analysis can help control smoke spread even during real large-scale fires, maintaining critical safe zones and saving lives and property. These serve as good models for designing structures across London and UK.

Conclusion

In summary, effective smoke ventilation through integrated natural and mechanical means has become indispensable for modern building fire safety. By controlling the spread and clearing of smoke through strategic openings and smoke exhaust systems, it enhances ability to evacuate occupants and conduct firefighting and rescue operations from survivable zones. Advances in intelligent controls, wireless sensors and technologies like drones could optimise smoke management further. Rigorous planning and implementation according to local fire codes guarantees buildings are equipped to minimise smoke hazards in case of fire emergencies. Thus, focusing on the smoke ventilation process plays a key role in protecting lives and mitigating damage from structure fires in London and across the United Kingdom.