BRIEF DESCRIPTION OF THE DRAWINGS
The method according to the invention will be explained in more detail hereinafter with reference to the figures, wherein:
FIG. 1 shows a section of a course over time of the oxygen concentration in a protected area, with the operating concentration and the control concentration of the oxygen content according to the first alternative of the inertization method according to the invention being maintained by means of a secondary source;
FIG. 2 shows a section of a course over time of the oxygen concentration in a protected area, with the operating concentration and the control concentration of the oxygen content according to the second alternative of the inertization method according to the invention being lowered to below the design concentration of the protected area; and
FIG. 3 shows a course of the oxygen content in a protected area, with the second alternative of the method according to the invention being implemented in the underlying inertization method.
DESCRIPTION OF THE INVENTION
FIG. 1 shows a section of a course over time of the oxygen concentration in a protected area, with the operating concentration BK and the control concentration RK of the oxygen content according to the first alternative of the inertization method according to the invention being maintained by means of a secondary source. In the illustrated graph, the y-axis represents the oxygen content in the protected area and the x-axis represents time. In the present case, the oxygen content in the protected area has already been lowered to a so-called full inertization level, i.e., to a control concentration RK that is below an operating concentration BK.
In the scenario illustrated schematically in FIG. 1, the operating concentration BK exactly corresponds to the design concentration AK. The design concentration AK is an oxygen concentration value in the protected area, which is in principle below a limit concentration GK that is specific for the protected area. The limit concentration GK, which is frequently also referred to as the “re-ignition prevention level”, relates to the oxygen content in the atmosphere of the protected area, at which a defined substance can no longer be ignited with a defined ignition source. The respective value of the limit concentration GK has to be determined experimentally and is the basis for determining the design concentration AK. For this, a safety margin is deduced from the limit concentration GK.
In principle, the operating concentration BK must not exceed the design concentration AK. When taking the safety concept for the inert gas fire extinguishing system and/or the employed inertization method into consideration, the operating concentration BK is obtained. In order to keep the operating costs of the inert gas fire extinguishing system as low as possible, it is preferred to select the margin between the operating concentration BK and the design concentration AK as small as possible because any decreases in the oxygen concentration beyond the required protected level are associated with increased use of extinguishing agents and/or inert gas.
In the course over time of the oxygen concentration illustrated in FIG. 1, furthermore, a control concentration RK is provided, which is in the center of a control range, the upper limit of the control range being identical to the operating concentration BK. The control concentration RK represents a concentration value, by which the oxygen concentration fluctuates in the protected area. It is provided that the fluctuations take place in the control range. When the oxygen content in the control range reaches the upper limit (in this case the operating concentration BK), then the oxygen content in the protected area is lowered again by feeding inert gas until the lower limit of the control range has been reached, whereupon further feeding of inert gas into the protected area is suspended. Accordingly, the upper limit of the control range corresponds to an upper threshold value for feeding the inert gas and the lower limit of the control range corresponds to a lower threshold value at which further feeding of the inert gas into the protected area is suspended. In other words, the upper threshold value corresponds to an activation of a primary or secondary source, and the lower threshold value corresponds to a deactivation of the primary or secondary source.
According to the invention, it is provided that even in the event of a failure of the primary source, the oxygen concentration can be maintained in the control range around the control concentration RK for a sufficiently long time. To this end, it is provided that the secondary source is configured redundant of the primary source. The time during which, by means of feeding inert gas from a primary source, and the emergency operation period during which the control concentration RK is maintained by the secondary source in the event of a failure of the primary source, is preferably long enough that an emergency operation phase is provided, during which the oxygen content in the protected area does not exceed the design concentration AK, and thus, the ignition of materials in the protected area continues to be prevented.
FIG. 2 shows a section of a course over time of the oxygen concentration in a protected area, with the operating concentration BK and the control concentration RK of the oxygen content according to the second alternative of the inertization method according to the invention being lowered to below the design concentration AK of the protected area. The difference to FIG. 1 is that in this case the design concentration AK no longer agrees with the operating concentration BK. Instead, the operating concentration BK and hence also the control concentration RK along with the associated control range are shifted downward, with the margin between the design concentration AK and the operating concentration BK corresponding to a failure safety margin ASA. In the scenario illustrated in FIG. 2, the oxygen concentration in the protected area is maintained in the control range around the control concentration RK by alternately turning the primary source on or off. To this end, it is provided that the failure safety margin ASA is selected such that in the event of a failure of the primary source the growth curve of the oxygen content in the protected area reaches the limit concentration BK and/or the re-ignition prevention level only in a defined period of time. This period of time is preferably selected such that an emergency operation phase is guaranteed, which is sufficiently long to continue to prevent the ignition and/or re-ignition of materials in the protected area before the fire prevention and/or fire extinguishing system is restarted.
FIG. 3 shows a course of the oxygen content in a protected area, the second alternative of the method according to the invention in the inertization method being implemented here. As already explained above in FIGS. 1 and 2, the y-axis represents the oxygen content in the protected area and the x-axis represents time. As shown in FIG. 3, initially an oxygen concentration of 21% by volume is present in the protected area.
Following an initial prophylactic lowering phase by a fire prevention system starting at the time to, the oxygen content in the protected area is reduced quickly to the control concentration RK. As illustrated, the oxygen concentration in the protected area reaches the re-ignition prevention level and/or the limit concentration GK at the time t1 and the control concentration RK at the time t2. The time period from t0 to t2 is referred to as the initial lowering phase.
In order to prevent materials present in the protected area from igniting following the initial lowering phase, a fire protection phase directly follows the initial lowering phase for the purpose of effective fire prevention. During this phase, the oxygen concentration in the protected area is maintained below the re-ignition prevention level and/or the limit concentration GK. Typically this occurs in that inert gas and/or oxygen-displacing gas is fed from the primary source into the protected area as needed in order to maintain the oxygen concentration in the control range around the control concentration RK and/or below the operating concentration BK.
In the event of a failure of the primary source, it is provided according to the invention that the failure safety margin ASA between the limit concentration GK and the operating concentration BK is so large that the growth curve of the oxygen content only reaches the limit concentration GK in a defined period z, thus achieving a sufficiently long emergency operation phase.
For explanation purposes it shall be pointed out that FIG. 3 illustrates the section that is shown in an enlarged scale in FIG. 2.
While there have been described what are considered to be exemplary embodiments of the invention, it will be apparent to those skilled in the art that various modifications may be made therein, and it is intended in the appended claims to cover such modifications and changes as fall within the scope thereof.
Patent Application
20080011492
