As modern buildings increase in height, the demands on their fire safety also grow, and traditional protection methods are increasingly proving insufficient. To effectively secure vertical escape routes, an approach based on precise airflow control and dynamic response to changing fire conditions is essential.

1. Introduction: the evolution of fire safety in high-rise buildings

Modern high-rise buildings are engineering marvels, yet their impressive scale introduces complex, often underestimated physical forces that can hinder the effectiveness of traditional safety systems. Statistics are clear: in 65–80% of cases, the direct cause of death in a fire is not the flames, but smoke. There is no single “universal” figure, as fire conditions, smoke toxicity, and reporting methods vary significantly across studies and countries. What is certain is that smoke spreads rapidly, and its density can reduce visibility to just a few centimetres, practically preventing evacuation even for occupants familiar with the building layout.

In response to this hazard, Staircase Pressurisation Systems – referred to in EN 12101-13 as Pressure Differential Systems (PDS) – have become the most effective method for protecting vertical escape routes. Unlike simpler smoke extraction systems, which remove smoke, PDS actively prevents smoke from entering protected zones, keeping stairwells and lift shafts free from toxic gases.

This article analyses and compares the implementation of pressure differential systems across several major, prestigious projects. Before delving into specific cases, it is essential to understand the physical phenomena, such as the stack effect, which challenge all smoke-control systems in tall structures.

2. Fundamental design challenge: the stack effect and its impact on pressure differential systems

Although pressure differential systems are highly effective, their performance in high-rise buildings depends on how they respond to changing external and internal conditions. The greatest of these challenges is the stack effect.

The stack effect is a directed movement of air in vertical spaces, such as stairwells, caused by differences in temperature, and therefore air density, between the interior and exterior of the building. This phenomenon is seasonal. In winter, cooler, denser external air enters the building at lower levels, warms up, rises, and generates overpressure at the top of the stairwell and underpressure at the bottom. In air-conditioned buildings during summer, the opposite effect is observed.

This uneven pressure distribution can lead to two critical situations in traditional PDS: 

• Underpressure: At lower levels, in the underpressure zone, the system may draw smoke from the fire zone into the protected stairwell, spreading lethal hazards throughout the building. 

• Overpressure: At higher levels, excessive pressure can prevent escape doors from opening (exceeding the allowable force of 100 N), effectively trapping occupants inside. 

The former EN 12101-6:2005 standard ignored this issue. Annexe B allowed the system to be started an hour before testing to equalise temperatures – a scenario entirely unrealistic in actual fire conditions. This permitted the acceptance of faulty installations. The new EN 12101-13 standard explicitly requires individual analysis for buildings over 60 metres tall, including advanced CFD (Computational Fluid Dynamics) simulations or additional mathematical analysis to verify design effectiveness. Similarly, BS 9991:2024 recommends PDS or MSVS particularly in high-rise residential buildings (over 30 m), while in both cases it is necessary to verify their effectiveness in buildings over 60m according to EN 12101-13 principles.

Recognition of this issue in 2008 triggered targeted research and development of a new generation of pressure differential systems by SMAY.

3. SMAY Innovation: From Full-Scale Research to the Patented SMAY Safety Way System

Overcoming the negative impact of the stack effect required a fundamental rethink of PDS concepts and a move away from static solutions. A full-scale, research-driven approach was necessary. This led SMAY to develop the Safety Way system and patent the iSWAY-FC® pressure differential device.

Central to this process was a two-year research project (2008–2010) conducted on a 92-metre test site at the Unity Tower in Kraków, known as “Skeleton”. The primary goal was to find an effective solution to mitigate the stack effect. Tests were carried out under all weather conditions to ensure reliability in real, dynamically changing circumstances.

The breakthrough was the development of the Flow System. Its concept uses two reversible units installed at the top and bottom of the stairwell. One unit supplies air, while the other extracts it, creating a controlled, directed airflow throughout the stairwell. This forced flow compensates for the natural pressure gradient caused by the stack effect, resulting in a stable and uniform pressure distribution throughout the protected space. The airflow direction is automatically determined by temperature sensors measuring the difference between internal and external air.

The technology implemented in modern iSWAY units has several key advantages:

• Predictive Algorithm: The system uses a patented, self-learning algorithm based on machine learning. Traditional systems, responding to door status changes, may “hunt” for the correctpressure, causing dangerous oscillations—pressure spikes preventing door opening (>100 N) or drops allowing smoke ingress. The predictive algorithm eliminates this, providing stable responsein under 3 seconds. 

• Wide Operating Range: The system operates from 200 m³/h to 50,500 m³/h, allowing precise compliance with both pressure criteria at low flow (closed doors) and velocity criteria at high flow (open doors). 

• Automatic Self-Tests: Daily autotests verify fan and damper operation and generate a report, meeting EN 12101-13 daily inspection requirements and ensuring continuous operationalreadiness. 

• System Approach: Assembling a system from individually certified components does not guarantee overall performance. All Safety Way components—from iSWAY units to sensors and dampers—are tested and certified as a complete set, analogous to buying a factory-tested car versus assembling one from random parts. 

The true measure of this technology is its successful application in Europe’s most demanding and prestigious architectural projects.

4. Analysis of implementations: safety way in practice

Varso Tower, Warsaw – protecting the tallest building in the EU

Project Context: Varso Tower, at 310 metres, is the tallest building in the European Union. 

Main Technical Challenges: Extreme height generated a very strong stack effect. A highly reliable and fast-responding system was required to protect complex escape routes for large numbersof occupants. 

SMAY Solution: The Safety Way system, based on the Flow System with reversible units, was implemented. It actively counters the stack effect, maintaining stable pressure across the full 310 metres, ensuring safe evacuation. A backup power supply controls system devices in fire mode and integrates with the building’s BMS in normal mode. Fire dampers and air dampers manage airflow, while fresh air intakes and exhausts remove hot gases from smoke channels. Varso Tower achieved WELL Health-Safety certification. 

Sky Tower, Wrocław – proven effectiveness in real hazard conditions

Project context: Sky Tower (212 m) is Poland’s tallest residential building. 

Real-world verification: System effectiveness was confirmed during an actual fire in the lift machine room on the 52nd floor, triggering evacuation of nearly 1,000 people. 

System performance: The Safety Way system responded exactly as designed, with the predictive algorithm acting in under 3 seconds and daily autotests ensuring readiness. Evacuation proceeded efficiently and without injuries. 

The Portal, London – adapting to the rigorous British market

Project context: The Portal is a 120-metre, 36-storey residential building in London. 

Challenges and technical requirements: Compliance with BS EN 12101-6 and BS EN 12101-13, mitigating the stack effect in a 120-metre structure, and designing effective air extraction paths. 

SMAY comprehensive solution: 

• iSWAY Units: 54 units, including 27 custom-built standby units. 

• Flow System: Fully counteracts the stack effect in stairwells and lift shafts. 

• Lobby Air Supply: Rapidly adapting system to manage pressure dynamics in lobby buffer spaces. 

• Active Air Extraction: Mechanical extraction system for corridors, ensuring reliable underpressure independent of wind effects. 

• Design Support: Full project support, including concept design, airflow calculations, CFD simulations, and technical documentation. 

These case studies collectively demonstrate the adaptability and reliability of the Safety Way system in extreme-height projects, compliant with international regulations and verified under real threat conditions. 

5. Synthesis of experience: how completed projects influence innovation and reliability

6. Conclusion: a holistic approach as the new standard for high-rise fire safety

Successful implementations at Varso Tower, Sky Tower, and The Portal clearly demonstrate that designing smoke control systems for high-rises requires more than powerful fans. It demands an intelligent, adaptive, fully integrated system functioning as a coherent whole.

Fire and smoke protection must consider the synergy of all components. SMAY’s approach to testing and certifying complete systems and designing based on evidence (flow calculations, case studies, CFD simulations) contrasts sharply with the riskier method of assembling systems from separately sourced components. The analogy is simple: it is the difference between buying a factory-tested car and assembling one from random parts.

Ultimately, success relies on close collaboration between architects, designers, and fire consultants from the earliest design stages. In the post-Grenfell era, where accountability and verifiable performance are paramount, such an evidence-based, holistic approach is the only responsible methodology for life-saving systems.

International knowledge exchange is also crucial. Each country has its own terminology, system testing methods, and assumptions about effectiveness. Limiting oneself to national standards may overlook proven solutions used elsewhere. SMAY provides international support at design@smay.eu.

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Staircase pressurisation system – knowledge base