FEMTC 2014

FDS Simulation of the Combined Use of Sprinklers and Water Mist Fire Extinguishing Systems

Csaba Szikra, Budapest University of Technology

Abstract

The purpose of this study is to investigate the effect of sprinkler water droplets with relatively large diameter on the movement of several orders of magnitude smaller water mist particles. The aim of the simulation is to analyze the flow field under a 1m x 1m shelf element with installation height of 1.5 m in the middle of the room, with and without n-heptane tray fire, using combined sprinklers and water mist extinguishing systems.

A CFD model, Fire Dynamic Simulator (FDS) version 5.5.3 was used for the numerical simulation. The data obtained from the numerical studies are analyzed.

As a result of the simulation, we have come to the following conclusions: water mist droplets of smaller diameter are forced to flow in the direction of the shelf environment by the sprinkler open-jet. Under the shelf, the velocities are higher than 1 m/s and vigorous turbulence can be observed. Water droplets of the mist can effectively reach a possible fire under tray. The results show that in the combined system, the sprinkler and water mist droplets can enhance each other’s effects.

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Integral Methodology for Fire Sprinkler System Design Following the Performance-Based Design Method

Juan Jose Zapata Franco, Universidad de los Andes

Abstract

This paper proposes a methodology for a thorough specification of sprinkler systems following the performance based method, by providing a theoretical approach into meeting the scenario’s phenomenological fire behavior with the system’s design features seeking to obtain personnel protection and fire suppression as design objectives. Specific design criteria are developed for the most important characteristics of a sprinkler system such as activation time, discharge coefficient k and spray density based on simulations and experimental correlations found in literature. Several experimental fire cases are studied to validate models, correlations and applying methods.

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Optimization of Smoke Ventilation Strategy in a Typical Underground Metro Station Fire

Muhammad Sontoso, Fire Safety Engineering Research Group, Universitas Indonesia

Abstract

Compartment fire is an unwanted event that needs to be accessed carefully in order to ensure the safety of occupants and structures. This study emphasizes on fire and smoke spreads in a typical underground metro station. Underground metro station usually has a geometry that will direct smoke in the same direction as the evacuation course. Thus, to secure safety of the passengers, the rate of the smoke spread and stratification should be reduces by well designed smoke ventilation systems. This paper examines the performance of ventilation configurations proposed for a typical underground metro station design. The study was carried out by using numerical model of Fire Dynamics Simulator version 6.0 and fire test in 1:25 bench scale of a typical metro underground station. Three ventilation configurations will be provided in this paper namely, mechanical ventilation, natural ventilation, and hybrid ventilation. The objective of this study is to formulate ventilation strategies in order to optimize the smoke handling capacity for lengthening the available safe egress time (ASET) during a fire event in a typical underground metro station. The discussion will also include the effect of hybrid ventilation on the occurrence of the pulsating phenomenon of smoke flow.

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A Partially-Stirred Batch Reactor Model for Under-Ventilated Fire Dynamics

Craig Weinschenk, National Institute of Standards and Technology

Abstract

When fire fighters arrive at a burning structure, the state of fire progression is usually under-ventilated, meaning the pyrolyzed fuel has consumed most, if not all, of the available oxygen inside the structure. These conditions are extremely hazardous for building occupants, who may be exposed to lethal concentrations of carbon monoxide (CO) and smokeproduced by fuel-rich combustion. Carbon monoxide inhalation remains one of the leading causes of fire fatalities. Modeling these scenarios is therefore of great interest to the fire community.

Under fuel-lean conditions, basic compartment fire dynamics is dominated by fast, heat-releasing reactions. These reactions cause thermal expansion of the surrounding gas mixture, thus generating buoyant plumes that entrain and efficiently mix the surrounding air with unburned fuel and hot combustion products. This mixture readily reacts, releases heat, and radiates back to the fuel source to complete the cycle. In these scenarios, a simple “mixed is burnt” approximation is often sufficient to model combustion chemistry. However, the quantitative prediction of CO presents a challenge to conventional fire models, because fuel-rich CO chemistry is relatively slow and highly temperature dependent.

As a step toward improved prediction of CO concentrations in under-ventilated compartment fires (which are low-Mach turbulent reacting flows), this talk presents a framework for transport, mixing, and reaction of chemical species in large-eddy simulation (LES). A partially-stirred batch reactor (PaSR) is adopted as a simple yet flexible model to treat a spectrum of complexity in the chemical reaction network, from mixture-fraction-based state relations to detailed chemical kinetics. Each computational cell is modeled as a PaSR. The PaSR model is implemented in a low-Mach LES solver called the Fire Dynamics Simulator (FDS). Verification and validation of this model within FDS will also be presented.

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Approach to Define the Aerodynamic Free Area for Natural Smoke Vents in a CFD Simulation Environment

Lajos Gábor Takács, Budapest University of Technology

Abstract

Provided naturally or mechanically, smoke and heat exhaust from buildings is one of the key application fields of CFD simulations. In an FDS/PyroSim environment, natural smoke vents may be modelled by simple openings called “Hole” elements, whose sizes are essential in the findings of simulation. In our paper, we propose a method to model natural flat roof ventilators in CFD simulation using a proper size.

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Modeling of Carbon Monoxide Dispersion from Vehicle Exhaust in a Partially-Enclosed Roadway Using FDS

Haavard Boehmer, Hughes Associates | RJA Group

Abstract

The design for a partially enclosed roadway raised concerns regarding the potential for development of hazardous carbon monoxide (CO) concentrations. The proposed roadway section is covered by buildings on three sides with one side open to a river. There were concerns that wind conditions may cause vehicle exhaust to become trapped in the roadway during stalled traffic conditions.

The interaction of wind with the roadway and the local cityscape creates a complex system. The potential for wind conditions that may confine CO to the roadway is difficult to accurately analyze solely based on engineering experience or using simple engineering correlations. Instead, Fire Dynamics Simulator (FDS) version 5.5 was used to model the dispersion of the vehicle exhaust. An FDS model was created that encompassed several hundred meters around the enclosed portion of the roadway up to a height of 80 m. The height was selected to capture the tallest buildings in the domain. Tall buildings surrounding the roadway were included in the model to approximate the wind conditions that would develop as closely as possible within the computational restrictions.

Dispersion of CO from stalled vehicles was modeled under a range of different wind scenarios selected based on a previous pedestrian wind study. Wind speed and direction were varied. Assumptions were made regarding the CO production of each vehicle, exhaust temperature and the density of vehicles in the tunnel.

Based on the FDS model results it was found that the critical limit for 15-minute average CO concentration of 120 ppm was never exceeded at any point. This analysis showed that the natural ventilation of the partially enclosed roadway was sufficient and no additional mechanical exhaust systems were required.

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Industry Accepted Design: A Case Study on Prescriptive vs. Performance-Based Design Criteria

Mackenzie Hill, Arup

Abstract

A prescriptive and performance based analysis has been conducted on a College Campus Building in Southern California. The building is proposed to be the center of operations as well as having administration facilities for the College. It will house an administrative office, production and support facilities. The project is three stories and includes a balcony that does not qualify as a story. The top floor is greater than 30 feet from grade and the largest floor has an area of approximately 12,500 square feet. The building is comprised of Group A and B occupancies in a separated mixed-use configuration. The building will be of Type II-B construction.

The prescriptive analysis has been evaluated based on the following systems:

  • Egress Components
  • Fire Rated Construction
  • Fire Alarm System
  • Fire Suppression System

The performance based analysis has been conducted for a number of fire scenarios using the following programs:

  • Fire Dynamics Simulator (FDS)
  • Simulation of Transient Evacuation and Pedestrian movementS (STEPS)

The required safe egress time (RSET) and available safe egress time (ASET) have been calculated and analyzed to determine if the fire and life safety goals have been achieved.

Based upon the performance-based analyses that were conducted for the building, it was evident that the performance-based design criteria applied to the analyses were more stringent than those inherent in the prescriptive design requirements. This paper will address the differences in industry-accepted design criteria for both prescriptive- and performance-based design solutions. Options for rectifying the difference in these criteria will also be presented.

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Pathfinder Verification and Validation Tests

Brian Hardeman, Thunderhead Engineering

Abstract

This presentation provides an overview of the verification and validation process for Pathfinder, and how it relates to the software development and automated quality testing process.

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Effects of Exit Discharge Congestion on the Effective Evacuation Time in a Typical Underground Metro Station Design

Yulianto Sulistyo Nugroho, Fire Safety Engineering Research Group, Universitas Indonesia

Abstract

Metro systems are being recognized as an effective and efficient way to solve transport problems in congested cities of the world. In emergencies such as those caused by fire, and power-cut is of utmost importance to have a well organized evacuation of passengers entrapped in an underground metro station building. Observation of fire emergency evacuation situations suggested the importance of managing the crowd on the ticket gates (usually on the concourse level) and the exit discharge on the ground level. The focus of this study is on the modeling of the effect of congestion in the exits discharge area on the effective evacuation time in a typical underground metro station fire. The results suggest that the projected maximum occupancy levels of an open space close to the exit discharge correlates with the movement capabilities of the evacuates at the corridors, stairs, escalators, and other facilities.

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Egress from a Hospital Ward: A Case Study

Grazia Carbotti, Università Campus Bio-Medico di Roma

Abstract

There are many issues in a hospital evacuation, related both to patients conditions and to building complexity. Moreover, as consequences of the fire, there may be delays in surgeries and in medical diagnoses or interruption of treatment for both inpatients and outpatients.

This work identifies and assesses problems that arise in the egress from the ward located at third floor of the University Hospital Campus Bio-Medico of Rome, using Pathfinder and its powerful tools.

First of all the structural design of the ward has been set, loading the maps in the software. The occupants have been described by their standards patterns (i.e.: nurse, doctor, geriatric inpatient, visitor) giving the real situation observed in a 2/3 days’ survey of the ward.

A maximum of 116 person could be found in the ward at its full capability. Five variables have been used to describe each type of occupant: speed, shoulder width, current door preference, reduction factor, comfort distance, giving to all the other variable the default value. Two different fire scenarios were created (fire in the electrical room and fire in the local kitchen) and consequently people had a different behaviour in each one. Finally, on the basis of the different type of actions that could be set in the software, a sequence of actions was created (for instance: wait, go to) for every single person. It was found that the time needed to fully evacuate the ward was of approximately 8 minutes, far behind the fire resistance time of the structures.

More than that, there was an overcrowded area in the ward that acted as a bottleneck: the smoke proof enclosure; this area is intended to separates the two nearby wards and, although built according to the Italian fire department regulation, it holds back people and beds. Some structural and technological solutions have been suggested on the basis of this outcomes.

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