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Building Safety: CFD Simulation For Fire Risk Management

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The deadly blaze at the 27-story Grenfell Tower in west London is one of at least a dozen fatal fires that have occurred worldwide since 2000. Despite the horrific scenes of Grenfell, UK regulations for tall buildings remain ahead of the curve in comparison with other countries around the world. In a post-Grenfell world, huge improvements continue to be made in construction materials and technological solutions, and testing and certification methods are sure to become even more rigorous, to ensure the quality of new products and materials.

In this article, we highlight how more accessible CFD simulation tools (like EXN/Aero) can play a key role in predicting and simulating the behavior of fire and smoke, assisting with the effective implementation of fire safety procedures. 

When it comes to fire risk management, builders and architects must follow three basic principles: 

  • Prevent risk of fire
  • Evacuate occupants safely and efficiently
  • Minimize damage to building and surrounding areas

However, this process becomes particularly challenging when updating older buildings to meet modern safety standards - an area that has come under close scrutiny in many countries during the past year. Whether new-build or retrofit, architects, builders and other experts must work closely to ensure evacuation and control systems are adequate for the individual building structure, function and its occupants. 

CFD Use For Fire Safety

Using CFD simulation for fire safety engineering isn't new in itself. In fact, the first use of computational fluid dynamics models to solve fire related problems can be tracked back to the 1960’s. CFD is one of the branches of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. While this sounds rather complicated, users of simulation no longer need to be engineers and university professors. The rapid development of commercial codes, an improved ease of use, and the emergence of the cloud has made simulation software more accessible, usable and affordable than ever before - hence why we're writing this article!

Put simply, fire modelling can be used to demonstrate that the proposed building design (or retrofit of an existing building) achieves a commensurate level of safety in accordance with the building regulations of that particular country. CFD helps fire safety engineers to determine fire and smoke behavior and assess the thermal response and analyze structural behaviors. This is useful predominantly due to the near impossibility of conducting realistic experiments on complete fire safety systems in a building.

Learn More About CFD Simulations

CFD Field Modelling vs Zone Modelling

Conventional fire and smoke control systems use pressure differences across small openings and cracks in physical barriers as a means to restrict smoke propagation from one space to another and water-spray curtains to diminish or eliminate fire and smoke. In the United States, most fire safety engineers depend upon the National Fire Protection Association (NFPA) guidebooks.

In turn these propose the use of simple zone models that solve conservation of mass and energy in a control-volume sense for each zone. One weakness of zone modeling is that momentum conservation is only captured through use of loss coefficient at openings. Traditionally, zone models have been faster than computational fluid dynamics based models, and have been used much more widely in this sector. However, atria, covered shopping malls, convention centers, airport terminals, sport arenas, and warehouses are just a few examples of large spaces for which these conventional zone-model approaches are not always effective. Additionally, vendors have worked hard to make modern CFD codes much faster.

CFD, often called “field-modelling” in the fire community to distinguish it form zone-modelling, has an unparalleled potential as an engineering estimator of fire consequence in atria since it permits specification of momentum conservation as well as much finer spatial and temporal resolution of the fire physics. In addition CFD approaches provide a link between outside building weather conditions and fire and smoke development.

aircraft_feature-e1528822893700CFD simulations can be used to predict the behaviour of fire and smoke in industrial buildings too, such as hangars & car parks.

Simulation For Safe Evacuation Procedures

One of the key uses of CFD simulation for fire safety is in investigating the time between when a fire starts until the conditions in an escape or queuing space become untenable. Also known as Available Safe Egree Time (ASET), three elements are most often considered:

  • Exposure to extreme heat
  • Exposure to toxic and irritant products
  • Loss of visibility
By considering the detection, pre-movement and movement times, the Required Safe Egress Time (RSET) can be estimated. Using CFD simulation, different fire and smoke scenarios can be considered and compared with occupant evacuation procedures to provide confidence that people could be safely removed from danger in all probable fire scenarios.
Screen Shot 2018-06-27 at 12.01.27
Classification of evacuation time components according to the SFPE Handbook of Fire Protection Engineering 
 
The simulation results will show the temperatures across escape routes and queuing areas, and through the prediction of fire and smoke behavior, levels of toxicity and irritancy can also be gathered. Smoke ventilation systems can be tested to draw conclusions about occupant visibility, enabling architects, engineers and builders to have confidence in their planned escape routes.
 

Minimizing Structural Damage

Simulation can provide a highly effective support tool when attempting to minimize the damage to a building structure and its surroundings. Through being able to predict the behavior of fire and smoke and test different scenarios, architects, builders and engineers can make informed decisions that could not only delay damage in specific areas of the building but even prevent it.

CFD Simulation: A Toolkit Essential

While there are still many factors one must take into account when assessing fire safety, such as fire growth rates of different arrangements of materials, CFD simulation has many advantages for those considering fire risk. In 2018, vendors like Envenio are presenting a wide range of tools that not only utilize the latest high performance computing, but are easier to use and more affordable than in previous decades. For this reason, there has never been a better time to adopt simulation into your work practices. 

In addition, at a time where structural safety is high on the global agenda, consultants and architects are making every effort to adopt the latest technology and resources to not only build more sustainably but also to potentially save lives. 

Discover The Benefits Of CFD

A modern CFD tool such as EXN/Aero provides the following advantages:

  • On-demand access for fire safety engineers, architects, consultants and those involved in the built environment.
  • Ability to utilize high performance software in the cloud without huge hardware investment.
  • Pay-as-you-go terms without expensive licenses - operating costs rather than capital expenditure.
  • Easy-to-use interface and extensive support for those without prior software experience. 
  • Services such as the Discovery Project, where simulations are carried out for you. 
  • Ability to solve challenges in the HVAC space quickly and efficiently. 

Try It For Yourself

There's no excuse to not being able to take advantage of simulation. Envenio has created the Discovery Project and Onboarding Program to further assist those without CFD experience. With the Discovery Project, Envenio executes a project on the client's behalf, returning engineering data and results according to an agreed set of objectives. With the Onboarding Program, Envenio works alongside the client to kick start their simulation project while training them fully on the platform. It guarantees the client is successful in using affordable simulation software tool, EXN/Aero, and minimizes the learning curve. 

        Our general purpose, cost-effective CFD, cloud solver reduces simulation times by up to 20x, and the platform includes a meshing tool, the solver, and a post-processing tool, as well as plenty of storage for your files. If you're working on a building project - or have any other HVAC CFD simulation requirements - why not try a free demo of EXN/Aero today and start using CFD for building design? 

Explore The Onboarding Program

References

NFP A 92B, Smoke Management Systems in Malls, Atria, and Large Areas, 2000, ”National Fire Protection Association, Quincy, MA, U.S.A. (2000)

Klote, J. H. and Milke, J. A., “Smoke Management in Atria and Other Large Spaces,” Design of Smoke Management Systems, ASHRAE, Atlanta, GA, U.S.A., pp. 101-134 (1992)

Tieszen, S. R., “On the Fluid Mechanics of Fires,” Ann. Rev. Fluid Mech. Vol. 33, pp. 67-92 (2001).

 

2018-07-9 | Categories: HVAC, architecture, BIM

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