Fire, Smoke, Explosion and Egress CFD Simulation Modelling

At Hegel, CFD is employed extensively to simulate Major Accident Hazards within the Commercial, Residential, Industrial, Oil & Gas and Marine 

industry, such as jet and pool fires within complex process areas. 

Fire, Smoke Explosion and Egress Simulation Modelling

 

Fire Detection & Protection System Specialist Contactor & Assistant

 

CFD Computational Fluid Dynamics for Fire, Smoke Explosion and Egress Simulation


Computational Fluid Dynamics (CFD) is a technique whereby the fundamental equations of fluid motion are solved within a computational domain. Meshing algorithms are used to subdivide the domain, which often comprises a large bounding box encompassing a simplified geometric representation of the relevant structures (such as an offshore platform), into millions of small control volumes. The CFD solver then iteratively solves the governing equations for mass, momentum and energy. As no assumptions are made a priori regarding the fluid flow with CFD, the number of modelling scenarios is potentially infinite. As such, CFD is an extremely versatile and useful engineering tool.

At Hegel, CFD is employed extensively to simulate Major Accident Hazards within the Commercial, Residential, Industrial, Oil & Gas and Marine industry, such as jet and pool fires within complex process areas. Results from CFD simulations often reveal important flow features not available from more simplistic phenomenological models, for example, the interaction of a flame with a platform structure or the complex nature of smoke dispersion leeward of an offshore platform. These results provide valuable insight for our clients into the nature of their particular scenarios.

Fire Modelling using CFD


The combustion of a jet or pool release can be incorporated into a CFD model through the use of a specialised combustion model. An account is taken of both the flame front and the dispersion of combustion products. Variations in hole/pool size, release location and direction, flow rate, blow-down systems and atmospheric conditions (such as wind direction and speed) can be included in the CFD simulation set. In summary, Hegel fire modelling capability includes:
 

  • Modelling of jet fire and pool fire releases for a variety of sizes and locations.

  • Incorporation of blow-down systems and failure scenarios (jet fires) through pseudo-transient and fully-transient simulations

  • Assessments of the impact of wind direction and speed.

Results from the CFD simulations provide important information for major accident hazard evaluation, including assessments of the effectiveness of proposed mitigation strategies. Key outputs from fire modelling simulations include:
 

  • Flame front, showing interactions with primary structures.

  • Temperature contours.

  • Thermal radiation flux contours.

  • Movies of flame development and regression due to the deployment of blow-down systems

Smoke Modelling using CFD

 

The internal and external dispersion of smoke following an accidental fire event often has significant safety implications, including escape impairment due to smoke inhalation or lack of visibility, ingestion of smoke into HVAC systems, and the detrimental effects on escape systems such as HeliOps or enclosed lifeboats. Although a combustion model may be used to represent the smoke source in CFD simulations, often a volumetric source of mass, momentum and heat are employed instead. Hegel has developed source models specifically for this purpose so that the smoke composition and flow rate can be calculated following fuel-rich or oxygen-rich combustion of complex hydrocarbon fuels.

Conventional outputs from CFD simulations include concentrations of the primary toxic gases within the smoke, particularly carbon monoxide (CO). However, Hegel has developed a technique whereby the combinative nature of hazards due to toxicants and irritants within the smoke (such as CO, carbon dioxide, oxygen-depletion, hydrogen cyanide etc.) are accounted for by calculating an overall time-to-incapacitation or time-to-death due to these effects. This gives an immediate indication as to escape or muster is possible and/or safe.
 

In summary, Hegel’s capability regarding smoke modelling includes:

 

  • Modelling of internal and/or external smoke dispersion following an ignited accidental release.

  • Definition of accurate volumetric smoke source terms including toxic gas concentrations.

  • Estimating smoke visibility within an internal structure, such as an accommodation block during a galley fire.

  • Incorporation of the effects of atmospheric conditions on smoke dispersion.

Key outputs from smoke dispersion analysis using CFD are:

 

  • Smoke concentration isosurfaces indicating the dispersion of the combustion products.

  • Concentration contours for various toxic gases.

  • Time-to-incapacitation and time-to-death contours due to smoke inhalation.

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