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Your Smoke Control FAQs Answered

We recently enlisted the help of our design team to address common smoke control FAQs. In this article we will delve into some of these FAQs about;

  • Computational Fluid Dynamics (CFD)
  • Components of a smoke control system,
  • The need for smoke control in buildings,
  • Pressurisation systems

Smoke Control FAQs 1: Computational Fluid Dynamics (CFD)

Smoke Control FAQsWhat is CFD?

CFD, or Computational Fluid Dynamics, is a computer simulation process that predicts the movement of energy, momentum, fluids (such as air), and substances (such as smoke particles and gases) within a given set of geometry limitations and boundary conditions. It helps determine what would happen in specific scenarios. In the context of smoke control system design, CFD is used to simulate different conditions and situations. This assesses the effectiveness and robustness of a system in protecting means of escape and facilitating firefighter access. It aids designers in making informed decisions and provides assurance to key stakeholders that the installed system is fit for purpose.

What are the crucial considerations in CFD modelling?

Firstly, it's important to note that due to the complexity of calculations involved, producing a CFD model can be time-consuming, even with powerful computers. Typically, we advise customers to expect results within 6 to 10 weeks. Secondly, obtaining accurate results depends on having the right information from the start and involving competent and experienced individuals to input the data. The more detailed the initial model, the more accurate the end results will be. Therefore, it's crucial to establish agreement among all relevant project stakeholders regarding the project parameters before initiating the modelling process.

Smoke Control FAQs 2: Components of a Smoke Control System

The components of a smoke control systemWhat are the essential components of a smoke control system?

In a natural shaft smoke ventilation system for multi-story buildings like offices or apartments, the key components include lobby ventilators with smoke control dampers installed at each level inside the smoke shaft. The damper on the fire floor opens when a smoke detector or fire alarm activates in the corridor or lobby being protected, while dampers on other floors remain closed. Additionally, to protect escape stairs, a natural system would have an Automatic Opening Vent (AOV) at the top of the staircase, which opens during a fire to allow smoke ventilation.

In cases where natural ventilation is unsuitable, mechanical fan sets can be installed. These offer advantages such as reducing the shaft size, which frees up more sellable or usable space within the building. However, since these systems are not prescribed, their performance should be verified using CFD modelling.

How do you determine the sizes of different components in a smoke control system?

Designers size up components based on building data, considering factors such as the presence of sprinklers, door heights, and floor plans. This information helps construct a CFD model to determine the appropriate volume flow rate required for the fans to operate. Ensuring the correct sizing of fans is crucial. An undersized fan may result in the system not meeting certification and specification requirements, while an oversized fan could lead to unintended door openings or difficulties for occupants trying to escape. Oversized fans also consume more energy and occupy more space. In many cases, oversizing can cause more issues than under-sizing.

The requirements for smoke control

Smoke Control FAQs 3: Smoke Control Requirements for Buildings

When is smoke control necessary in a building?

Smoke control is necessary in various types of buildings, including those with firefighting cores, which typically apply to buildings taller than 18m, basements deeper than 10m, or buildings with multiple basement levels exceeding 900m² in floor area. Multi-story, multi-occupancy residential buildings may also require smoke control in stairs, corridors, and lobbies. Shopping centres, theatres, covered or underground car parks, basements larger than 200m², atria breaching compartmentation, and buildings employing smoke control as part of their fire strategy are among other examples. For specific requirements pertaining to different building types, feel free to contact us.

What are the smoke control requirements for residential buildings?

The smoke control requirements for residential buildings depend on factors such as building height, corridor length, and the number of stairs. Recommendations and standards, such as Grenfell and BS 9991 (Code of Practice for Residential Buildings), are subject to updates. Further details will be provided in subsequent blogs once the standard reaches publication.

Do other building types have specific smoke control requirements?

Yes, specific smoke control requirements apply to basements, warehouses, and buildings with atria. To learn more about the requirements for a particular building type, please reach out to us.

Smoke Control FAQs 4: Pressurisation Systems

What is a pressurisation system?

A pressurisation system supplies clear air to a protected space, increasing the pressure within that area to prevent smoke from entering. For a detailed explanation of how a pressurization system works, you can read more about it in this blog.

When is a pressurisation system necessary?

In the UK, pressurisation systems are commonly employed when traditional natural or mechanical smoke ventilation solutions are unsuitable or non-compliant. They may also serve as an alternative to discounting a staircase when planning and sizing evacuation routes. The latest draft of BS 9991 also recommends pressurisation for single stair residential buildings over 18m, but please note that this is a draft format and subject to potential changes.

What are the requirements for a pressurisation system?

Colt Pressurisation System

The primary requirements for pressurisation systems can be found in standards such as BS EN 12101-6: 2005 (soon to be replaced by BS EN 12101-6 & 13: 2022). These standards outline how to design a pressurization system for various building types. Key requirements include maintaining the correct pressure within the stair core when doors are closed, achieving the appropriate air velocity across specific doors when they are open, and ensuring the maximum door opening force is not exceeded.

When designing a pressurisation system to meet all requirements, consider factors such as the ingress and smoke-free status of pressurization air, management of airflow differences between closed and open door conditions, maintenance of air movement (including the need for air release paths when achieving desired air velocities), estimation of air loss through leakage calculations, and the availability of space for equipment.

For more information on any of the above topics, please don't hesitate to contact one of our technical consultants by emailing info@gsstothers.com or calling us at 028 4277 2931 .

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