A Waypoint-Based Approach to Assessing Visibility for Performance-Based Fire Safety Design

Core Concepts

This study presents an innovative method to assess visibility along egress routes in performance-based fire safety design, utilizing data from numerical fire models. The approach adopts Jin's law for scenarios with inhomogeneous smoke distributions, as derived from CFD simulation results, and introduces a waypoint-based approach to evaluate visibility.

Abstract

The key highlights and insights of this content are:

Visibility maps are introduced as a novel approach to assess the accessibility of egress routes in the presence of fire-induced smoke. These maps indicate safe areas along evacuation paths, with respect to visibility.

The method calculates the available visibility at each location as an integrated value of the extinction coefficient along the line of sight to the closest exit sign, considering factors like view angle and visual obstructions.

The required visibility is determined by the distance between the observer and the exit sign, in accordance with Jin's law. This eliminates the need for predefined performance criteria.

The approach allows for temporal visibility assessment, enabling ASET-RSET analysis. It can be implemented as a post-processor for results data from numerical fire simulations, currently supporting FDS.

Compared to traditional local assessment of visibility, the method provides a more realistic and distinct evaluation of egress scenarios, reducing personal bias in the interpretation of simulation results.

A grid sensitivity analysis is performed, highlighting the influence of the CFD model discretization on the visibility assessment. The results demonstrate the advantages of the waypoint-based visibility maps over direct interpretation of local visibility.

The visibility maps and ASET maps generated by the method can reveal potential hazards, such as blind spots, that may not be recognized in a local assessment of visibility. They also provide insights into areas where occupants are likely to be exposed to enhanced smoke concentration.

Stats

"Visibility is significantly reduced by eye irritating effects when the smoke density exceeds a certain threshold."
"At the same smoke density, black smoke allows for a greater visibility than white smoke."
"The visibility for red signs within smoke with predominantly scattering properties (white smoke) is 20 - 40% higher, and within predominantly absorbing smoke, it is 20 - 30% higher."

Quotes

"Jin's law is still widely used to assess visibility in performance-based fire safety design. It also serves as a standard model in numerical fire models such as the Fire Dynamics Simulator (FDS)."
"Visibility maps enable a more realistic and distinct assessment of egress in case of fire, considering smoke induced reduction of visibility. No performance criteria need to be defined due to the automated consideration of the building's architectural characteristics."

Key Insights Distilled From

A waypoint based approach to visibility in performance based fire safety design

by Kris... at arxiv.org 04-18-2024

https://arxiv.org/pdf/2404.11439.pdf

Deeper Inquiries

How can the proposed visibility assessment method be extended to incorporate the vertical viewing angle and its impact on the perception of exit signs?

Incorporating the vertical viewing angle into the proposed visibility assessment method can enhance the accuracy of the visibility maps, especially in scenarios where the observer's line of sight is not parallel to the floor level. To extend the method to include the vertical viewing angle, the following steps can be taken:

Adjustment of Observation Height: The observer's eye level should be considered at a specific height above the floor, and this height should be taken into account when calculating the line of sight to the exit signs. By adjusting the observation height, the impact of vertical viewing angles can be accounted for in the visibility assessment.

Three-Dimensional Modelling: Implement a three-dimensional approach to calculate the line of sight from the observer to the exit signs, considering both horizontal and vertical angles. This would involve creating a more detailed representation of the building geometry and the location of the exit signs in three dimensions.

Ray Tracing: Utilize ray tracing techniques to simulate the path of light rays from the observer to the exit signs, taking into account the vertical viewing angle. By tracing the rays in a three-dimensional space, the visibility assessment can more accurately reflect the real-world conditions of occupants trying to locate exit signs in a smoke-filled environment.

Integration with Building Information Modeling (BIM): Incorporate BIM data to accurately represent the vertical layout of the building, including the heights of floors, ceilings, and exit signs. By integrating BIM data, the visibility assessment method can account for the vertical viewing angles and provide a more comprehensive analysis of visibility in complex building structures.

By extending the visibility assessment method to include the vertical viewing angle, the accuracy and reliability of the visibility maps can be improved, leading to a more realistic evaluation of occupant safety in fire scenarios.

How can the visibility maps approach be applied to complex, multi-story building designs with dynamic fire scenarios?

Applying the visibility maps approach to complex, multi-story building designs with dynamic fire scenarios presents several challenges and considerations. Some potential limitations and challenges include:

Vertical Visibility Assessment: In multi-story buildings, the visibility assessment needs to account for visibility across different floors and levels. This requires a three-dimensional analysis of the building geometry and the placement of exit signs on each floor.

Dynamic Fire Scenarios: Dynamic fire scenarios, such as the spread of fire and smoke over time, can impact visibility conditions. The visibility maps need to be updated in real-time to reflect changing conditions during a fire event.

Integration with Fire Dynamics Simulation: The visibility maps approach should be integrated with fire dynamics simulation models to accurately predict the spread of smoke and its impact on visibility in multi-story buildings. This integration requires a detailed understanding of fire behavior and smoke movement in complex building structures.

Evacuation Simulation: Combining visibility maps with evacuation simulations can provide a comprehensive analysis of occupant safety in dynamic fire scenarios. The evacuation simulation should consider the visibility conditions to assess the effectiveness of evacuation routes and the time needed for occupants to reach safety.

Human Behavior Factors: Consideration of human behavior factors, such as panic reactions and decision-making under stress, is crucial in complex, multi-story building designs. The visibility maps should account for how occupants may react to reduced visibility and the impact on their ability to navigate to safety.

By addressing these challenges and considerations, the visibility maps approach can be effectively applied to complex, multi-story building designs with dynamic fire scenarios, providing valuable insights into occupant safety and egress strategies.

How can the visibility maps and ASET maps be integrated with evacuation simulations to provide a comprehensive analysis of occupant safety in performance-based fire safety design?

Integrating visibility maps and ASET maps with evacuation simulations can enhance the analysis of occupant safety in performance-based fire safety design by considering both visibility conditions and evacuation dynamics. Here's how this integration can be achieved:

Visibility-Aware Evacuation Modeling: Incorporate the visibility maps into the evacuation simulation software to simulate how reduced visibility impacts occupants' ability to navigate to safety. By considering visibility constraints in the evacuation modeling, the simulation can provide more realistic scenarios of egress under limited visibility conditions.

ASET-RSET Analysis: Use the ASET maps to determine the available safe egress time (ASET) based on visibility criteria and compare it to the required safe egress time (RSET). By integrating the ASET maps with evacuation simulations, the analysis can assess whether occupants can evacuate safely within the available time considering visibility constraints.

Dynamic Visibility Updates: Update the visibility maps in real-time during the evacuation simulation to reflect changing visibility conditions as occupants move through the building. This dynamic visibility assessment can provide insights into how visibility impacts evacuation efficiency and safety.

Scenario-Based Analysis: Conduct scenario-based analysis by combining visibility maps, ASET maps, and evacuation simulations for different fire scenarios and building layouts. This comprehensive analysis can help identify critical areas with poor visibility and assess the effectiveness of evacuation strategies under varying conditions.

Occupant Behavior Modeling: Integrate models of occupant behavior, such as decision-making and movement patterns, into the evacuation simulations. By considering how occupants react to reduced visibility and other factors, the analysis can provide a more realistic assessment of occupant safety in performance-based fire safety design.

By integrating visibility maps and ASET maps with evacuation simulations, a comprehensive analysis of occupant safety in performance-based fire safety design can be achieved, taking into account visibility constraints, evacuation dynamics, and human behavior factors.