Fire Safety and Smoke Management with CFD Analysis

BlogCFDFire Safety and Smoke Management with CFD Analysis

Fire safety is a crucial characteristic of any inhabited space, especially of those with high risks such as large people capacity, difficult exit paths or presence of flammable materials. Architects and engineers must ensure that a place is safe for its occupants under both normal and emergency conditions. Construction and life-saving codes impose requirements on features such as the capacity of means of egress, but also on the performance of smoke management through ventilation, temperature control, and visibility in case of fire. Here, two study cases explore the use of online simulation with the SimScale cloud-based platform in order to assess code compliance and safety of closed spaces quickly and accurately. 


Learn how to optimize HVAC systems for fire safety and smoke management using cloud-based CFD simulation with SimScale.


Fire Safety & Smoke Management Case Study 1: CO Extraction in a Parking Garage

The first case considers a car parking garage where the carbon monoxide (CO) concentration is controlled with a forced ventilation system. Said CO concentration levels need to meet threshold level values (TLV) imposed by code regulation. This target concentration maximum levels impose our main design constraint.

On the other hand, the same ventilation system is used for smoke management in the event of a fire in the garage. In that case, the CO production source is assumed to be a source of smoke, and the same airflow pattern (and simulation project) can be used to assess the performance.

The considered model conditions include:

Fire safety and smoke management using cfd for parking garage
Figure 1: Case 1 – parking garage geometry and boundary conditions

A computational fluid dynamics (CFD) simulation is carried out to explore CO levels under the described normal operating conditions. The simulation was implemented in the SimScale cloud computing platform, using the CFD scalar transport module.

Ventilation Performance

The simulation results allow us to plot the air flowing velocity magnitude and directions:

Airflow velocity, CFD simulation for fire safety and smoke management
Figure 2: Airflow velocity plot showing velocity magnitude (color scale) and direction (black arrows)

By checking the results, it is found that low flow velocity zones (blue colored areas) are present:

  1. At the vicinity of the ramp
  2. At the center-right, where a recirculation zone also occurs

By examining CO concentration levels, it is revealed that these zones also constitute the areas of maximum concentration:

smoke management in parking garage using cfd simulation, image showing CO concentration plot
Figure 3: CO concentration plot, clipped at the TLV value

It is found that the study case exceeds the TLV for maximum CO concentration which is 1600 PPM, and the design needs to be improved.

Design Optimization for Ensuring Fire Safety

The strategy implemented to meet the objective of lowering the maximum CO concentration level in the garage is to place jet fans to generate airflow in the high concentration, low-speed zones. The proposed locations for the fans are displayed in the following figure:

Jet fans placement to improve airflow in a garage, CAD model
Figure 4: Jet fans placement to improve airflow in the garage.

The CFD simulation is run again to include fans in the garage design. By looking at the new air flow velocity plot, the effect of the fans can be appreciated:

Airflow velocity plot showing velocity magnitude and direction at the jet fans height for a parking garage
Figure 5: Airflow velocity plot showing velocity magnitude (color scale) and direction (black arrows), at the jet fans height

Now the effect of the improved ventilation system on the CO concentration levels can be checked. The CO concentration plot shows that now the TLV criteria is met:

CO concentration plot for the improved design of a parking garage for efficient smoke management
Figure 6: CO concentration plot for the improved design.

The results found show that with the design optimization implemented, a reduction of more than 55% in the maximum CO concentration level in the garage was achieved:

Comparison of maximum CO concentration levels between original and improved design
Figure 7: Comparison of maximum CO concentration levels between original and improved design.

To learn more about smoke simulation along with heat and smoke extraction, check out this blog


Fire Safety & Smoke Management Case Study 2: Fire Scenario in a Parking Garage

In this case, a fire safety scenario in a car park facility is analyzed. The computer simulation is implemented using FDS (Fire Dynamic Simulator), a CFD tool specially tailored for fire-driven fluid flow (smoke and heat transport). FDS is optimized to bring a more efficient, specialized workflow for the analysis of fires. For this project, FDS was run in the SimScale cloud-based simulation platform. The FDS tool is not currently available for public usage but in a closed test phase.

The considered model includes the principal geometry features and the following conditions:

CAD model of the fire scenario study case for a parking garage
Figure 8: Model of the fire scenario study case

Smoke Propagation

The first results of the simulation present the smoke propagation pattern, which allows assessing the smoke management of the ventilation system. Here the time evolution of concentration can be examined to detect danger zones. Plots for smoke propagation after five and ten minutes are presented:

Simulation of smoke concentration five minutes after a fire starts in a parking garage
Figure 9: Smoke concentration five minutes after the fire starts
Simulation of smoke concentration ten minutes after a fire starts in a parking garage
Figure 10: Smoke concentration ten minutes after the fire starts

It can be seen that after ten minutes, the only areas with fresh air are close to air inlets. It is also found that the smoke is distributed in more than 80% of the area after 15 minutes, and reaches a steady state after 25 minutes.

Temperature Distribution

The calculated temperature distribution shows that after ten minutes, high levels are confined to the fire source area and that exit zones keep low levels, as shown in the following plot:

Temperature distribution ten minutes after a fire starts, simulation of a garage
Figure 11: Temperature distribution ten minutes after the fire starts

Visibility

Another interesting result of the simulation is the sight visibility at every point, which is an important safety factor in case of fire. In the following plot, red areas have high (clear) visibility and blue areas have low (bad) visibility:

visibility analysis with CFD in a fire safety and smoke management case
Figure 12: Visibility at a height of 1.8 meters, 25 minutes after the fire starts

It is found that the visibility is more than 10 meters in the entire area until the 5 minutes mark. After 5 minutes, the visibility drops below 10 meters in the left corners of the garage.

Ventilation Airflow

The airflow velocity plot shows the action of the jet fans and the general ventilation pattern:

airflow velocity magnitude at jet fans location height, parking garage analysis in case of fire
Figure 13: Airflow velocity magnitude at jet fans location height

Conclusion

Two study cases for fire safety and smoke management assessment were performed. It was found that by using CFD simulation tools, code compliance can be easily checked. Also, design improvement opportunities are easily identified and optimizations tested for performance evaluation.

To learn more about CFD simulations like airflow simulation check out our public projects. 


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