Flow Systems is one of fire ventilation solutions, which allow to limit the flow of smoke through the air stream of sufficient velocity, the supply in the opposite direction to the incoming smoke. A typical and original using a flow systems to protect against smoke were tunnels, where is produced critical velocity air flow. According to the NFPA 130 standard, the concept of critical velocity is to set minimum air stream flow velocity used for ventilation, moving toward the source of the fire, which is required to prevent smoke from his movement in a direction opposite to the incoming air (called backlayering). There are several mathematical relations allowing the critical speed calculation depending on the fire size design and dimensions of tunnel. The smoke behavior when critical air flow velocity was used is shown in figure.
For several years, these systems are also commonly used for protecting car parks against smoke. Then the systems ventilation are called streaming. These solutions make possible to focus the smoke flow in the direction to the exhaust points in the car parks, while maintaining free from smoke the car parks. The smoke behavior when used the critical air flow velocity is shown in the figure below.
