الفهرس 
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Abstract
to cause accidents that threat human’s life and properties. Therefore increasing research
work has been directed towards the field of fire science in an attempt to minimize the fire disasters and their consequent damage. Fire suppression systems are an extremely important part of every building that ensures
the safety of the occupants and limits damage due to fire. Water mist systems use pressurized nozzles which release water droplets of different sizes. The mist encapsulates the fire and as it turns to vapor, it removes heat from the source. As the mist turns to
steam, it expands immensely forcing oxygen away from the flame. This deprives the fire of necessary oxygen to quench itself over time. Fire suppression by using a mix of water
mist together with nitrogen gas is investigated in this study.
The study is carried out using Fire dynamic simulator (FDS - PYROSIM program). The program achieves fire scenario and fire extinguishment requirements. The FDS is also
used for the smoke flow modeling in different ventilation conditions, tunnel fires and multi-floor buildings. Due to the FDS code development and model validation, the capability for predict the performance of fire suppression study by using different water
mist systems has been significantly improved. The dimensions of the fire dynamic simulator “FDS” model standard hanger are based on a 1/5 scale of typical industrial building model (hanger), its triangle polygon ceiling is made of gypsum board, and its rectangular base is of dimensions (6.0m x 2.0m) and itsheight is (2.5m). Its opening door dimensions is (0.6m x 0.5m), and it has 6 opening
windows, 3 on left wall and other 3 windows on triangle ceiling (all windows have the same dimensions 0.75m x 0.3m).
It is built for predicting geometry of fire spread and particles distribution of water mist along with using nitrogen gas. The heat release is obtained from a cubic burner of (0.2m) side length that used nylon fuel and a heat release of 500 kW, that is kept constant
throughout the study. All results are based on above scaled described standard model simulation for various water mist characteristics in addition to different proportions of nitrogen gas along with fire source position. The model is subjected to study different
cases. The nozzles inject a mixture of different proportions of nitrogen gas to water mist, vary from (1:6, 1:3, 1:2, 2:3, 1:1, 2:1). The tiny droplets of water mist are also vary from 50 μm
to 30 μm. After the nitrogen gas has entered the injection area, it quickly combines with the room air and reduces the oxygen volume fraction. Thereby it absorbs heat in the area,
trying to suppress the flame. In addition, the evaporation of these tiny droplets of water mist can reduce quickly the fire temperature, meanwhile the water mist effect is like the
physical effect of using a gas on fire extinguishment that could reduce the concentration of oxygen, beside its very excellent performance of blocking the transfer of thermal radiation
which can block effectively the intense heat radiation.The present work has employed the ”FDS – PyroSim program” to analyze the computational design, the spread of fire and distribution of particles. It is used in modeling
the present standard hanger building, through studying the effectiveness of using different
ratios of Nitrogen gas flow rate injection compared with water mist flow rate amount at various water mist particles size and different fire source positions such as center and
corner on fire extinguishing time, that shows a pronounced optimum ratio results of 1:1.The results showed that time of fire suppression is decreasing with decreasing water droplet size and increasing the water mist flow rate. The best mixing ratio of Nitrogen gas
with water mist is found to be 1:1 for minimum suppression time 175 seconds. The total optimum Nitrogen flow rate is 60 l/min, the diameter of the water droplet is 50 µm, and of
total flow rate 60 l/min.