Active fire prevention

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In contrast to "reactive fire fighting " by fire extinguishing systems or fire brigades , which only react to fires that have already broken out, an active fire prevention system actively excludes fires from the outset by reducing the oxygen content in the area to be protected.

Mode of action

By supplying the inert gas nitrogen, the oxygen content is systematically reduced from almost 21 % by volume (natural ambient air) to the amount that makes a combustion reaction impossible. The nitrogen displaces the calculated part of the oxygen , and a fire-safe atmosphere is created . The oxygen concentration must be adapted to each substance or any physical state. For a large part of the solids it can be assumed that approx. 16% by volume of oxygen is sufficient to protect the material. Many plastics require 15% by volume.

In the case of liquids and gases, the concentration must be reduced further. The explosion factor has to be included here. If the explosion is also to be excluded and not just the fire, two concentrations can be specified. In order to safely avoid a fire in a liquid, approx. 14% by volume of oxygen is still permitted, but an explosion can only be ruled out at concentrations of 8 to 10% by volume. For gases, this concentration is 5% by volume (the lower explosion limit of hydrogen, the most dangerous gas, is given as 5.4% by volume). Thanks to the permanently controlled supply of nitrogen, the active fire prevention system keeps the oxygen content of the air in the protected area permanently at a reduced level. The active fire prevention system can be set up with little effort if the rooms to be protected have little traffic and a relatively high level of impermeability, such as automated deep-freeze stores and cold stores or hazardous material stores and automated high-bay warehouses.

Components

An active fire prevention system essentially consists of a nitrogen generator, an air compressor and oxygen sensors with a monitoring and control unit.

An alternative method for generating nitrogen in active fire prevention systems is the use of fuel cells , which produce electricity in addition to the low-oxygen air.

function

The active fire prevention system generates the nitrogen for the oxygen reduction directly on site using a nitrogen generator or a fuel cell (whose natural, low-oxygen exhaust air has a high proportion of nitrogen). The monitoring and control unit of the active fire prevention system continuously controls the oxygen content of the air. In the nitrogen generator, normal outside air is compressed and dried in a compressor, cleaned of particles and residual oil in the filter unit and separated into nitrogen and residual gases in hollow fiber membranes . While the residual gases are discharged into the open, the nitrogen replaces part of the room air in the protected area and thus reduces the amount of oxygen required for independent combustion. Sensors continuously measure the oxygen content of the air in the protected area. The nitrogen supply is regulated by a solenoid valve regulated by the monitoring and control unit . When the set oxygen concentration is reached, the active fire prevention system automatically switches to stand-by mode. It only becomes active again when the oxygen concentration rises again, for example due to leaks in the building or open doors and gates.

Personal security

Areas protected by active fire prevention systems remain accessible and can be used almost without restriction. Nitrogen is completely harmless at normal atmospheric pressure. Since it occurs to 78% by volume in the natural atmosphere , the human body is optimally adapted to nitrogen. The reduction in the oxygen content to 15% by volume, for example, achieved by the active fire prevention system with the aid of nitrogen corresponds approximately to the atmospheric conditions at an altitude of 3,000 meters. Oxygen reduction is therefore safe for healthy people if certain precautionary measures are taken.

literature

  • Adam Merschbacher: Fire Protection Primer. Everything about fire protection and prevention, Springer Vieweg-Verlag, ISBN 978-3658211387 .
  • Hans-Joachim Gressmann: Defensive and technical fire protection for architects, civil engineers and fire-fighting engineers. 2nd revised and expanded edition, expert Verlag, Renningen 2008, ISBN 978-3-8169-2778-5 .

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