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CFD Analysis

– COMPUTATION FLUID DYNAMICS (CFD), EVACUATION AND ZONE MODELLING –

– A BRIEF OVERVIEW –

SIMULATIONS

Generally computer models serve to demonstrate performance objectives of a given building through the relevant design parameter

inputs, design fire criteria and tenability requirements. This will form part of a wider assessment of the building and will often serves to compare the required safe egress time (RSET) against the available safe egress time (ASET).

RSET AND ASET

If the ASET found to be greater than the RSET then the performance

objectives can be considered effectively demonstrated. The RSET can be approximated by hand calculations, or through use of movement simulation software such as Pathfinder (in which the evacuation of a building during the worst case or highest occupancy can be simulated with a degree of realism). The ASET is the point at which the tenability limitations are exceeded for one or more criteria such as the fractional effective dose of Carbon Monoxide (FEDco) or when the Visibility drops below a certain threshold.

ZONE MODELLING AND CFD

For simple designs Zone modelling can be a quick, painless and acceptable approach, but for more complicated building geometries such as atria, or tunnels for example, CFD models are required to provide realistic results.

This approach is useful in the application of specific designs of buildings that fail to meet the prescriptive guidance. Here are a few examples of the types of projects were we have used CFD modelling to support a performance based design:

  • University Atria
  • Railway Station Mezzanine
  • Shopping Centers
  • Prisons
  • Junior Schools

Fire-Q can provide this CFD or Zone modelling as part of the overall fire strategy or as a standalone service. Please contact us now for a free initial consultation.

EXAMPLE PROJECTS

Bowes Street, Manchester

Project Type: CFD Study

Fire-Q were engaged to perform a fire engineering technical CFD (computational fluid dynamics) study for the proposed development at Bowes Street in Manchester. The travel distances of the corridors were greater than the limit for escape routes given in Approved Document B Volume 2. To compensate for this, CFD was employed to find the most cost-effective options for designing the smoke control system.

A combination of natural smoke ventilation, mechanical smoke ventilation and sprinklers systems were assessed via CFD modelling to ensure a fire would not impose an unacceptable level of risk to any persons. The performance objectives of the system were to maintain the staircase relatively free of smoke and to ensure the specified tenable limits for means of escape and fire service operations are provided within the corridors.

The design requirements of smoke ventilation systems and sprinkler systems were given according to the results of the CFD models and appropriate recommendations were given to design safe escape routes in case of a fire inside the building.

Mint Lane, Lincoln

Project Type: CFD Study

Studio Map Ltd approached Fire-Q for a fire engineering CFD modelling study for the proposed development at Mint Lane in Lincoln.

The travel distance of the corridor was greater than the limit for escape routes in one direction given in Approved Document B Volume2. The installation of a fire engineered mechanical smoke ventilation system (MSVS) was recommended to compensate for the extended travel distance. According to the BS 9991, an extended corridor is acceptable if the provided MSVS can meet the tenability criteria (such as temperature and visibility) given in PD 7974-part6.

CFD simulations were undertaken to evaluate requirements of smoke ventilation systems to ensure fire did not impose an unacceptable level of risk on any persons. Different positions for mechanical and natural ventilation systems were tested to design safe escape routes and to reduce the required mechanical flow power. The design requirements of the smoke ventilation system were given according to the results of the CFD models. Illuminated signs were also added to the design to improve visibility of the escape routes in case of a fire.

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