• Fire Science and Engineering
• /
• v.16 no.1
• /
• pp.1-7
• /
• 2002

Halogen-based fire suppressing agents have environmental problems because they cause the stratospheric ozone depletion and globe warming. Hence, fire suppression system using fine water mist became the center of interest as a substitution of halon. As a study about this, it is in progress to make the optimum droplet size by using water mist nozzles and to improve the extinguishing performance of water mist by using additives. Before this study, the extinguishing time of ethanol and n-heptane pool fire was measured with changing of water mist droplet size, flow density, discharge pressure, and fire size. In this study, on adding the additives to improve physical and chemical extinguishing performance of water mist, the extinguishing performance would evaluate and the optimum condition would find out. As a result, in case of ethanol pan 1 pool fire, the extinguishing time of the water mist by adding of 2.5 wt% NaCl and 0.3% AFFF got shorter 27% and 60% than the pure water mist. Adding of AFFF was to decrease the flame temperature by forming thin film on the fuel surface and to decrease the evaporation of n-heptane fuel. In case of NaCl, alkali salt crystals showed on the flame surface.

• Fire Science and Engineering
• /
• v.26 no.4
• /
• pp.55-62
• /
• 2012

The suppression mechanisms of carbon dioxide ($CO_2$) as a representative fire suppression agent were revisited using a counterflow diffusion flame which could be applied the concept of a local application system. To end this, the low strain rate $CH_4$/air counterflow diffusions with $CO_2$ addition in either fuel or oxidizer stream were examined numerically using detailed-kinetic chemistry. Radiative heat loss due to radiating gas species including $CO_2$ added was considered by the optically thin model (OTM). As a result, the critical $CO_2$ volume fractions in the oxidizer stream required to extinguish the flame were in good agreement with the experimental data reported in the literature, while somewhat under-prediction was observed with $CO_2$ added in the fuel stream. The surrogate agents were adopted to estimate the quantitative contribution with changing in global strain rate ($a_g$) on the flame extinguishment among pure dilution effect, thermal effects including radiation heat loss and chemical effect due to the $CO_2$ fire suppression agent.

• Transactions of the Korean hydrogen and new energy society
• /
• v.25 no.2
• /
• pp.161-172
• /
• 2014

Hydrogen, which can be produced from abundant and widely distributed renewable energy resources, seems to be a promising candidate for solving the concerns for improving energy security, urban air pollution, and reducing greenhouse gas emissions. The two primary motivating factors for hydrogen economy are fossil fuel supply limitations and concerns about global warming. But the safety issues associated with hydrogen economy need to be investigated and fully understood before being considered as a future energy source. Limited operating experience with hydrogen energy systems in consumer environments is recognised as a significant barrier to the implementation of hydrogen economy. To prevent unnecessary restrictions on emerging codes, standards and local regulations, safety policies based on real hazards should be developed. This article studies briefly the direct impact-distances from hazard events such as hydrogen release and jet fire, and damage levels from hydrogen gas explosion in a confined space. Based on the direct impact-distances indicated in the accident scenarios and consumer environments in Korea, the safety policies, which are related to hydrogen filling station, hydrogen fuel cell car, portable fuel cell, domestic fuel cells, and hydrogen town, are suggested to implement hydrogen economy. To apply the safety policies and overcome the disadvantages of prescriptive risk management, which is setting guidance in great detail to management well known risk but is not covering unidentified risk, hybrid risk management model is also proposed.

• Fire Science and Engineering
• /
• v.23 no.1
• /
• pp.55-62
• /
• 2009

A general combustion characteristics of forcing nonpremixed jet in laminar flow rates have been conducted experimentally to investigate the effect of forcing amplitude with the resonant frequency of fuel tube. There are two patterns of the flame lift-off feature according to the velocity increasing; one has the decreasing values of forcing amplitude on the lift-off occurrence when a fuel exit velocity is increasing, while the other has the increasing values. These mean that there are the different mechanisms in the lift-off stability of forced jet diffusion flame. Especially, the characteristics of attached jet flame regime are concentrically observed with flame lengths, shapes, flow response and velocity profiles at the nozzle exit as the central figure. The notable observations are that the flame enlogation, in-homing flame and the occurrence of a vortical motion turnabout have happened according to the increase of forcing amplitude. It is understood by the velocity measurements and visualization methods that these phenomena have been relevance to an entrainment of surrounding oxygen into the fuel nozzle as the negative part of the fluctuating velocity has begun at the inner part of the fuel nozzle.

• Journal of the Korean Society of Safety
• /
• v.19 no.3 s.67
• /
• pp.124-129
• /
• 2004

To evaluate the numerical method in simulation of diffusion flames and to see the effects of strain rate and fuel concentration on the flame radius and thickness, the nonpremixed methane-air counterflow flames in microgravity were simulated axisymmetrically by using the MST Fire Dynamics Simulator (FDS). The $1000^{\circ}C$ based flame radius and thickness were investigated for the mole fraction of methane in the fuel stream, $X_m=20,\;50,\;and\;80\%$ and the global strain rates $a_g=20,\;60,\;and\;90s^{-1}$ for each mole fraction. The flame radius increased with the global strain rate while the flame thickness decreased linearly as the global strain rate increased. The flame radius decreased as the mole fraction increased, but it was not so sensitive to the mole fraction compared with the global strain rate. Since there was good agreement in the nondimensional flame thickness obtained with OPPDIF and FDS respectively, it was confirmed that FDS is capable of predicting well the counterflow flames in a wide range of strain rate and fuel concentration.

• The Korean Journal of Ceramics
• /
• v.4 no.4
• /
• pp.279-285
• /
• 1998

The $UO_2$ pellets are usually sintered under hydrogen gas atmosphere. Hydrogen gas may cause unexpected early failure of the refractory bricks in the sintering furnace. In this work, nitrogen was mixed with hydrogen to investigate the effect of nitrogen gas on a failure machanism of the refractory bricks and on the microstructure of the $UO_2$ pellet. The hydrogen-nitrogen mixed gas experiments show that the larger nitrogen the mixed gas contains, the less the refractory materials are reduced by hydrogen. The weight loss measurements at $1400^{\circ}C$ for fire clay and chamotte refractories containing high content of $SiO_2$ indicate that the weight loss rate for the mixed gas is about half of that for the hydrogen gas. Based on the thermochemical analyses, it is proposed that the weight loss is caused by hydrogen-induced reduction of free $SiO_2$ and/or $SiO_2$ bonded to $Al_2O_3$ in the fire clay and chamotte refractories. However, the retardation of the hydrogen-induced $SiO_2$ reduction rate under the mixed gas atmosphere may be due to the reduction of the surface reaction rate between hydrogen gas and refractory materials in proportion to volume fraction of nitrogen gas in the mixed gas. On the other hand, the mixed gas experiments show that the test data for $UO_2$ pellet still meet the related specification values, even if there exists a slight difference in the pellet microstructural parameters between the cases of the mixed gas and the hydrogen gas.

• Fire Science and Engineering
• /
• v.27 no.2
• /
• pp.62-69
• /
• 2013

In this study, a full scale experiment was carried out to analyze the heat and smoke movement. The experiment was conducted a kindergarten that is scheduled to reconstruction. The kindergarten is a two-story building and the area of each floor is 252 $m^2$. 36 l heptane was used as a fuel and heptane was burned in a 0.8 m square steel pool. Maximum heat release rate was 1.7 MW at natural condition. Smoke movement and temperature variation were measured during the experiment. In the first floor corridor, smoke was moved downward about 1.4 m at 1 minute after a fire. Corridor was filled with smoke at 4 minutes after a fire. In the second floor, temperature was maintained at $70^{\circ}C$ or less. But, second floor rooms were filled with smoke.

• Fire Science and Engineering
• /
• v.29 no.5
• /
• pp.34-41
• /
• 2015

The applicability of plate thermometer (PT), which feature simple installation and low cost, was experimentally examined in steady and unsteady-state fire conditions. An infrared radiation heater and a square burner with C3H8 as fuel were used as heat sources. The relative measurement accuracy of the PT was evaluated by comparing measurements made using a Gardon-type heat flux meter. From a practical point of view and in terms of measurement accuracy, the optimal size and thickness of the PT in steady and unsteady-state fire conditions were 100 mm and 0.6 mm, respectively. These results can be explained by the conductive heat losses and thermal inertia of the PT for different sizes and thicknesses. It can be also concluded that measurements of heat flux using the PT in conditions of faster fire growth rate than slow require considerable attention.

• Fire Science and Engineering
• /
• v.25 no.3
• /
• pp.51-56
• /
• 2011

The full-scale experiments are carried out to investigate the fire suppression characteristics of water-based fire fighting systems in a road tunnel. Applied systems are the low-pressure water spray system at 3.5 bar and the high-pressure water mist system at 60 bar. The water flow rate of the high-pressure system is one sixth only of the water spray system. A passenger car and a heptane fuel pan with area of $1.4m^2$ are used as fire sources. A blower system is installed at the tunnel exit to realize the longitudinal ventilation conditions (0.9~3.8 m/s) in the tunnel. Temperatures from the fire source to the down-stream direction are measured by K-type thermocouple trees. The experimental results show that the cooling effect of the high pressure water mist system in the test conditions were equivalent to that of the low pressure water spray system for B-class fire.

• Fire Science and Engineering
• /
• v.32 no.4
• /
• pp.7-16
• /
• 2018

In this study, the prediction performance of design fire curves (DF) was evaluated for gas fires in a compartment by using CFAST. The CFAST simulations adopted the 2-stage DF suggested by the previous study and the Quadratic and Exponential DF suggested by Ingason. It was found by comparing the simulation and experimental results that the overall prediction performance of the design fire cures for the spatially-averaged temperature and concentrations of $O_2$ and $CO_2$ was, from the most reasonable to the most inaccurate, 2-stage DF > Quadratic DF > Exponential DF. The CFAST simulation could not predict for the difference in the spatially-averaged temperature and concentrations of $O_2$ and $CO_2$ at door and inner side locations in a compartment. The CFAST simulations also showed a limitation in the prediction of the spatially-averaged temperature at lower layer and the concentration of CO.