Mechanical smoke ventilation system design for common escape routes using CFD

  • BS 9991 & BS 9999 & SCA guidance
  • Approved Document B
  • Technical guidance document B
  • Extended travel distances
  • Use of mechanical system in lieu of natural
  • Equivalency for non-compliant building layout
  • Protected Lobbies / Stairs / Corridors
  • Push / Pull / Pressurization / Depressurization
  • Tenability during escape and firefighting
  • Performance based design

Computational Fluid Dynamics (CFD) simulations can be used to demonstrate the performance of mechanical smoke ventilation systems to approving bodies. It is required when a natural smoke shaft is being replaced by a mechanical smoke shaft or for the approval of non-code-compliant building layouts, for instance when travel distances are extended.

Interested in a mechanical smoke shaft ventilation analysis

Tenable conditions on escape routes

Staircases and common circulation areas are crucial paths for both evacuees and firefighters in case of fire. Although the intention is to limit the smoke spread, opening doors while escaping or during firefighting may allow smoke to reach a wider area. This potentially hinders the escape from other flats or parts of the building and/or access of firefighters.

Therefore a fire strategy of a building requires maintaining common circulation areas, such as corridors and stair cores free of smoke and heat.

Mechanical smoke shaft in lieu of a natural system

Smoke ventilation in compliance with building codes can be accomplished by having travel distances within limits and ventilate corridors with natural shafts. However, it is often more practical to install a mechanical smoke ventilation system instead of the natural shaft that requires a significant amount of space and needs to follow a straight trajectory. British standards require that, when a mechanical smoke ventilation system is used in lieu of a natural system, the mechanical system should demonstrate an equivalent or better performance compared to a natural system.

Extended travel distances

Furthermore, when travel distances within corridors or lobbies are extended, the smoke ventilation system must be upgraded to maintain tenable conditions within these zones during both the escape and firefighting phase. A well-designed mechanical ventilation system should ensure effective use of openings, avoid dead spots and limit pressures to prevent excessive forces when opening doors.

The main objectives are:

  • Verify that the stairs are kept clear of smoke
  • Verify the tenability on escape routes during escape and firefighting phases
  • Verify the maximum allowed door opening forces are not exceeded due to large pressure differentials
  • Verify that the mechanical system demonstrates an equivalent or better performance compared to a natural system

What do we offer

We have an in-depth knowledge of Fire Safety Engineering and a long history in the application of CFD in this field. A significant increase is seen in performance-based building designs being put into practice. Developments in engineering tools and the higher performance of calculation computers allow for going beyond the back-of-the-envelope methods and allow designers to push the boundaries of their building design. One Simulations makes use of industry-leading calculation software and performs calculations on an in-house dedicated high-performance computing (HPC) cluster. This allows us to increase accuracy, with significantly reduced simulation run times and thus shorter turnover times.

Aside from executing the calculations, our team also regularly performs third-party reviews for CFD projects. We can review CFD simulations executed in any software, such as Ansys CFX, Fluent, Fire Dynamics Simulator (FDS), OpenFOAM, etc. See also second opinion services.

While our work cost-effectively gives freedom to designs, the results are reported with a focus on code compliance and legislative requirements.

Feel free to contact us at an early stage so that we can share our knowledge and experience with you.

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