EP1550481A1 - Inerting method for decreasing the risk of a fire - Google Patents

Abstract

The firefighting system uses carbon dioxide, nitrogen or some other suitable inert gas to flood a room which is on fire. Output of gas from a pressure vessel dilutes the oxygen concentration in the room from the normal 21% by volume to below e.g. 12%. The flooding phase (t0,t1,t2) may take approximately 120 seconds, after which the oxygen level reaches a lower threshold (Unterer Schwellwert) and the gas is turned off. Air may leak in, raising the oxygen level. When it reaches an upper threshold (Oberer Schwellwert), the gas is turned on again until the lower level is reached. After a given time (t3), the primary source of inert gas is exhausted, and the oxygen concentration slowly rises toward a maximum safe level (Sicherheits Abschlag S).

Description

The present invention relates to an inertization method for reducing the risk a fire in an enclosed protected area, where the oxygen content in the protection area with a predeterminable control range by introducing a Oxygen displacing gas from a primary source for a certain time is maintained at a control concentration below an operating concentration, and a device for carrying out the method.

Inertisation procedure for fire prevention and extinguishing in closed rooms are known from the fire extinguishing technology. The resulting in this process Extinguishing effect is based on the principle of oxygen displacement. The normal ambient air is known to 21 vol .-% of oxygen, to 78 vol .-% of Nitrogen and 1 vol .-% of other gases. For deleting, by initiating from Z. As pure nitrogen as inert gas, the nitrogen concentration in the relevant Room further increased and thus reduces the oxygen content. It is known, that a extinguishing effect begins when the oxygen content is below about 15% by volume decreases. Depending on the flammable materials in the room can also further lowering the oxygen content to, for example 12 vol .-% may be required. At this oxygen concentration, most can combustible materials stop burning.

The oxygen-displacing gases used in this inert gas extinguishing technique are usually stored in special ancillary rooms in steel cylinders compressed. It is also conceivable, a device for generating an oxygen-displacing To use gas. These steel bottles or this device for the production of oxygen displacing gas constitute the so-called primary source of Inertgasfeuerlöschanlage. If necessary, then the gas from this primary source via piping systems and directed corresponding outlet nozzles in the space in question.

The associated inert gas fire extinguishing system usually has at least over a facility for the sudden introduction of the oxygen displacing gas from the Primary source in the room to be monitored and a fire detection device for detecting a fire characteristic in the room air.

For laying out the entire fire prevention or inert gas fire extinguishing system The highest possible level of safety includes a technical and logistic system Planning in the event of plant shutdown as a result of incidents to the to meet safety requirements. Even if during the Designing the fire prevention or inert gas fire extinguishing system all measures be considered, which allow a restart of the system To achieve as fast and seamless, brings the inerting by means of However, inert gas technology has certain problems and points in terms of reliability clear boundaries. So it has been shown that it is possible, the Inertgasfeuerlöschanlage to conceive such that the probability for the Occurrence of an accident during the lowering or regulation of the oxygen content in the protection area to one below an aforementioned operating concentration lying rule concentration is relatively low, but there is often a Problem in it, the control concentration for a long time, during the so-called Emergency operation phase to maintain the required value, in particular therefore, because in the known from the prior art inerting no Possibility of early exceeding a level of re-ignition of the To prevent oxygen concentration in the protected area, if due to an accident the primary source fails completely or at least partially.

The re-ignition phase is the period after the fire-fighting phase, in which the oxygen concentration in the protected area a certain Value, the so-called re-ignition prevention value, must not exceed to avoid reignition of the materials in the protected area. The re-ignition prevention level is an oxygen concentration that depends on the fire load of the protected area and determined on the basis of tests becomes. According to the VdS guidelines, the oxygen concentration must flood when the protection zone is flooded in the protection area, the re-ignition prevention level of, for example 13.8 Vol .-% achieved within the first 60 seconds from the start of flooding (firefighting phase). Furthermore, the re-ignition prevention level within 10 minutes after the end of the firefighting phase be crossed, be exceeded, be passed. It is envisaged that within the firefighting phase the fire in the protected area is completely extinguished.

In the known from the prior art inerting is at a Detection signal the oxygen concentration as quickly as possible to a so-called Shut down operating concentration. The required inert gas comes from the primary source of the inert gas fire extinguishing system. Under the term "Operational concentration" is understood to mean a level below a so-called Design concentration is. The design concentration is an oxygen concentration in the protected area, in which the inflammation of everyone in the protected area existing substance is effectively prevented. In determining the design concentration A protection range is usually added by the limit value an ignition of any materials in the protected area is prevented, nor a deducted for security deduction. After reaching the operating concentration in the protected area usually the oxygen concentration is on a held at an operating concentration control concentration.

The control concentration is a control range of the residual oxygen concentration in the inertized Protection range within which the oxygen concentration during the Reflux phase is held. That control range is defined by an upper limit, the switch-on threshold for the primary source of inert gas fire extinguishing system, and a lower limit, the switch-off threshold of the primary source of the inert gas fire extinguishing system, limited. During the reignition phase, the control concentration becomes held by repeated introduction of inert gas in this control range. That Inert gas usually comes from serving as the primary source reservoir of the Inertgasfeuerlöschanlage, i.e., either the device for generating oxygen displacing gas (e.g., a nitrogen generator), gas cylinders or others Buffer means. In case of malfunction or malfunction now the danger that the oxygen concentration in the protected area rises early and the Rebound prevention level exceeds, thereby reducing the reignition phase is shortened and successful firefighting in the protected area is not more can be guaranteed.

Based on the previously described problems with regard to the safety-related Requirements of an inert gas fire extinguishing system or an inerting process The present invention is based on the object from the state to further develop the inertization process known to the art and explained above, that even when one of the primary source is concerned Incidentally, the emergency operation phase is sufficiently long to cause inflammation or re-ignition effectively prevent combustible materials in the protected area. Another object is to provide a corresponding inert gas fire extinguishing system for Specify the execution of the procedure.

This object is achieved in an inerting process of the type mentioned solved according to the invention as the first alternative in that the control concentration maintained in case of failure of the primary source for a Notbetriebszeit by a secondary source becomes.

This object is further achieved in that in the aforementioned Inertisierungsverfahren the control concentration and the operating concentration under Forming a fault tolerance distance so far below that for the protected area fixed design concentration can be lowered, that the rise curve of the Oxygen content in case of failure of the primary source one determined for the protection area Limit concentration reached only in a given time.

The technical problem underlying the present invention is further solved by an apparatus for carrying out the above-mentioned method, which is characterized in that the primary source and / or the secondary source an oxygen displacing gas generating machine, a bottle battery, a buffer volume or an oxygen depriving or similar machine is.

The advantages of the invention are, in particular, that an easy to implement and very effective inerting method for reducing the risk of Brandes is achievable in an enclosed protection area, whereby even in an accident, i. For example, in case of failure of the primary source, from which the Adjusting the control concentration used in the protected area is inert gas, the Maintain control concentration for an emergency operating time by means of a secondary source will (alternative 1). The term "primary source" is in this context to understand any inert gas reservoir, e.g. a nitrogen generator, a gas cylinder battery in which the inert gas is in compressed form, or another buffer volume. In the analogous sense, the term "secondary source" a redundant from the primary source reservoir, which in turn, for example may be a nitrogen generator, a bottle battery or any buffer volume, to understand. An essential aspect of the present invention is that that the secondary source is designed to be redundant from the primary source, thus to decouple both systems from each other and the susceptibility of the inertization process to reduce. It is provided that the secondary source in such a way is designed to the control concentration in case of failure of the primary source for an emergency operating time maintain, which is sufficiently long, for example, at least a 10-minute re-ignition phase or an 8-hour emergency operation phase in the To be able to provide protection in which the oxygen content in the protected area does not rise above the reburn prevention level. Of course it is here also conceivable, the secondary source according to any emergency operating time interpreted.

For example, in the second alternative, the limit concentration is around the re-ignition prevention level of the shelter. Here it is an oxygen concentration, which ensures that flammable substances of the protection zone can no longer be ignited. It is provided, the operating concentration from the beginning to reduce so much that the increase curve the oxygen concentration reaches the limit only after a certain time. This predetermined time is for example 10, 30 or 60 minutes for a fire extinguishing system and 8, 24, or 36 hours for a fire prevention facility to service personnel arrives with spare parts, and thus enables a realization of a Reflux phase or emergency operation phase in which the oxygen content is not rises above a rebound prevention level, and thus effectively ignites or reignition of fires in the protected area prevented. Because of this so-called "lowering" the operating concentration, i. by setting the Operating concentration with formation of a failure safety distance below the Design concentration of the shelter, will be an alternative to those described above Embodiments of the inertization process according to the invention which also ensures that if the primary source fails an emergency operating time the oxygen concentration below a specified value, in advantageously below the re-ignition prevention level. Of course, here is also conceivable, both alternatives to each other combine. In order to extend the emergency operating time, it is also possible that additional Measures, such as the imposition of operating restrictions, such as the temporary reduction of the commission.

With the device according to the invention is a way to carry out the indicated above. It is envisaged that the Primary source and / or the secondary source any reservoir, such as a machine, which produces an oxygen-displacing gas, a bottle-type battery in which the inert gas is in compressed form, another buffer volume, or else is also an oxygen depriving or similar machine. Instead of an oxygen It is also conceivable to generate oxygen in the room air withdraw, for example with the help of fuel cells. Come as secondary sources both stationary and mobile devices in question, such as Extinguishing agent tanks with evaporator on a truck. Switching between the Primary and secondary sources are either manual or automatic.

Preferred developments of the invention are with respect to the method in the dependent claims 2 and 4 to 9 indicated.

Thus, it is preferably provided for the method that the operating concentration is the same or approximately equal to a design concentration set for the protection zone is. Through this development of the method it is possible to reduce the consumption of Inert gas or extinguishing agent for the protection area optimally reduce by the Operating concentration set to an oxygen concentration in the protected area becomes, with which the substances of the protection area just ignite to let. To determine the design concentration is in a preferred manner of the concentration at which the substances of the protection zone no longer exist ignite, deducted a discount.

Particularly preferably, the failure safety distance is determined taking into account a valid for the protection area air exchange rate, in particular an n ₅₀ - value of the protection area, and / or the pressure difference between the protection area and the environment. In order to allow the most accurate adaptation of the method according to the invention to the relevant protection area, it is provided that the failure safety distance is greater, the greater the n ₅₀ value of the target area.

In order to achieve a further increase in the reliability of the system, it is particularly preferred that the design concentration be lowered by a safety margin below the limit concentration determined for the protection zone. Thus, for example, it can be ensured during the time until the secondary source is made available that the oxygen content remains below the re-ignition prevention level or the limit concentration. Thus, it is conceivable that the safety discount is determined taking into account the limit concentration and / or the air exchange rate n50; ie S = α ([O _{2, air} ] - GK), where S is the safety margin, [O _{2, air} ] is the oxygen concentration in the air of the protected area, GK is the re-ignition prevention level and α is a given factor. For example, for α = 20%, [O _{2, air} ] = 20.9% by volume, GK = 16% by volume, a safety discount of S = 1% by volume results and for α = 20%, [O _{2, air} ] = 20.9 vol.%, GK = 13 vol.%, A safety discount of S = 1.6 vol.%.

In a particularly preferred embodiment, a detector for detecting further a fire characteristic provided, the oxygen content in the protected area when detecting an incipient fire or a fire quickly on the control concentration is lowered if the oxygen content previously at a higher Level was. Through this development of the inertization process according to the invention It is now possible, for example, in a multi-stage process Implementing inertization procedures. Thus, according to the invention, that the protection area initially, for example, a visit by persons to admit to a correspondingly higher level. This higher level Either the concentration of the room air (21 Vol .-%) or a first or Grundinertisierungsniveau be, for example, 17 vol .-%. So it is conceivable that First, the oxygen content in the protected area to a certain basic inerting level lowered, for example, 17 vol .-% and in case of fire the oxygen content to a certain Vollinertisierungsniveau further on the control concentration is lowered. A basic inertization level of 17% by volume oxygen concentration means no danger to persons or animals, so that they can still easily enter the room. Setting the Vollinertisierungsniveaus or the rule concentration can either after detection an incipient fire are set, but it would be conceivable here also, that this level is set, for example, at night, when no people enter the room in question. At the control concentration is the flammability of all the materials in the shelter so much degraded that they themselves can not ignite anymore. By providing a redundant secondary source or alternatively by lowering the oxygen concentration achieved in an advantageous manner that the reliability of the inerting process is significantly increased, thus ensuring that even in case of failure of the primary source there is adequate fire protection.

Preferably, the control range is about ± 0.2 vol.%, And preferably at most ± 0.2 Vol .-% oxygen content around the control concentration in the shelter. in this connection it is an area covered by an upper and a lower one Threshold is defined, which is about 0.4 vol .-% and preferably at most 0.4 vol .-% apart. The two thresholds indicate the residual oxygen concentrations, in which the secondary source is turned on or off to the To maintain or reach setpoint if the primary source fails. Of course But here also other orders of magnitude for the control range are conceivable.

In order to achieve the best possible adaptation of the inerting process to the relevant protective space, it is provided in a preferred embodiment of the inerting process according to the invention that the regulation of the oxygen content in the protected area takes into account the air exchange rate, in particular the n ₅₀ value of the protected area and / or the pressure difference between protected area and environment. This is a value that describes the ratio of the generated leakage volume flow in relation to the existing volume of space at a pressure difference to the environment of 50 Pa generated. The n ₅₀ value is thus a measure of the tightness of the protected area and thus a decisive factor for dimensioning the inert gas fire extinguishing system or for the design of the inertization process with regard to the reliability of the primary source. In a preferred manner, the n ₅₀ value is determined by means of a so-called BlowerDoor measurement, in order to be able to assess the tightness of the enclosing components bounding the protected area. In this case, a standardized overpressure or underpressure of 10 to 60 Pa is generated in the protected area. The air escapes through the leakage surfaces of the enclosing components to the outside or penetrates there. A corresponding measuring device measures the required volume flow to maintain the pressure difference of, for example, 50 Pa required for the measurement. Subsequently, a measuring program calculates the n ₅₀ value, which refers to the generated pressure difference of 50 Pa in a standardized manner. The BlowerDoor measurement is to be carried out before the concrete design of the inertization method according to the invention, in particular before the design of the inventively provided, redundant from the primary source secondary source or before the design of the fail-safe distance in the alternative inertization.

In a particularly preferred further development of the method according to the invention, it is provided that the calculation of the extinguishing agent quantity for maintaining the control concentration in the protected area takes place taking into account the air exchange rate n ₅₀ . Accordingly, it is possible to design the size or the capacity of the primary source and / or the secondary source as a function of the n ₅₀ value and thus adapted exactly to the protected area.

The method according to the invention will be explained in more detail below with reference to the figures.

Fig. 1

einen Ausschnitt eines zeitlichen Verlaufs der Sauerstoffkonzentration in einem Schutzbereich, wobei die Betriebskonzentration und die Regelkonzentration des Sauerstoffgehalts gemäß der ersten Alternative des erfindungsgemäßen Inertisierungsverfahrens mittels einer Sekundärquelle aufrechterhalten werden;

Fig. 2

einen Ausschnitt eines zeitlichen Verlaufs der Sauerstoffkonzentration in einem Schutzbereich, wobei die Betriebskonzentration und die Regelkonzentration des Sauerstoffgehalts gemäß der zweiten Alternative des erfindungsgemäßen Inertisierungsverfahrens unter die Auslegungskonzentration des Schutzbereichs gesenkt werden; und

Fig. 3

einen Verlauf des Sauerstoffgehalts in einem Schutzbereich, wobei die zweite Alternative des erfindungsgemäßen Verfahrens in dem zugrundeliegenden Inertiserungsverfahren implementiert ist.

Show it:

Fig. 1

a section of a time course of the oxygen concentration in a protected area, wherein the operating concentration and the control concentration of the oxygen content according to the first alternative of the inertization process according to the invention are maintained by means of a secondary source;

Fig. 2

a section of a time course of the oxygen concentration in a protected area, wherein the operating concentration and the control concentration of the oxygen content are lowered below the design concentration of the protected area according to the second alternative of the inerting process according to the invention; and

Fig. 3

a course of the oxygen content in a protected area, wherein the second alternative of the method according to the invention is implemented in the underlying Inertiserungsverfahren.

Fig. 1 shows a section of a time course of the oxygen concentration in a protection range, wherein the operating concentration BK and the control concentration RK of the oxygen content according to the first alternative of the invention Inertisierungsverfahrens be maintained by means of a secondary source. In In the plot shown, the ordinate axis represents the oxygen content in the Protective area and the abscissa axis is the time. In the present case is already the oxygen content in the protected area to a so-called Vollinertisierungsniveau lowered, i. to a control concentration below an operating concentration BK RK. In the scenario shown schematically in Fig. 1 corresponds to the Operating concentration BK exactly the design concentration AK.

The design concentration AK is an oxygen concentration value in the protected area, basically below a limit concentration specific to the protection area GK is lying. The limit concentration GK, which is also often called "rebound prevention level" is called, refers to the oxygen content in the atmosphere the scope of protection, where a defined substance with a defined Ignition source just can not be ignited. The respective value of Limit concentration GK must be determined experimentally and forms the basis for the determination of the design concentration AK. This is done by the limit concentration GK deducted a haircut.

The operating concentration BK must not be greater than the design concentration AK. The operating concentration BK results under consideration the safety concept for the inert gas fire extinguishing system or the inerting process used. To the operating costs of the inert gas fire extinguisher as possible to keep low, is preferably the distance between the operating concentration BK and the design concentration AK as small as possible, because over the necessary level of protection beyond lowering the oxygen concentration an increased use of extinguishing agents or inert gas entail.

In the time course of the oxygen concentration shown in FIG. 1 Furthermore, a control concentration RK specified, the center in a control range is, where the upper limit of the control range is identical to the operating concentration BK is. The control concentration RK represents a concentration value by which the oxygen concentration fluctuates within the protection range. It is intended that the fluctuations take place in the control area. Reach now the Oxygen content in the control range the upper limit (here the operating concentration BK) so the oxygen content in the protected area by introducing inert gas again lowered until the lower limit of the control range is reached, whereupon a further introduction of inert gas is stopped in the protection area. Consequently The upper limit of the control range is an upper threshold for the Introducing the inert gas and the lower limit of the control range a lower Threshold, in which a further supply of the inert gas in the protected area is omitted. In other words, this means that the upper threshold activate a primary or secondary source and the lower threshold Disabling the primary or secondary source is equivalent.

According to the invention, it is now provided that even if the primary source fails, the Oxygen concentration in the control range around the control concentration RK around for a sufficiently long time can be maintained. It is intended that the secondary source is redundant from the primary source. The time in which by introducing the inert gas from a primary source and the emergency operating time, in which in case of failure of the primary source, the control concentration RK by the Secondary source is maintained, is advantageously so long that an emergency phase is provided, in which the oxygen content in the protected area the design concentration does not exceed AK and thus ignition of Materials in the protected area continue to be prevented.

FIG. 2 shows a section of a time profile of the oxygen concentration in FIG a protection range, wherein the operating concentration BK and the control concentration RK of the oxygen content according to the second alternative of the invention Inerting process below the design concentration AK of the protected area be lowered. The difference to Fig. 1 lies in the fact that in this case the Design concentration AK no longer coincides with the operating concentration BK. Instead, the operating concentration is BK and thus the control concentration RK with the associated control range moved down, where the Spacing between the design concentration AK and the operating concentration BK corresponds to a fail-safe distance ASA. In that shown in FIG Scenario, the oxygen concentration in the protected area by alternately Turning on or off the primary source in the control area around the Control concentration RK held around. It is provided that the Ausfallssicherheitsabstand ASA is chosen such that in case of failure of the primary source, the rise curve of the oxygen content in the protected area, the limiting concentration BK or reaches the re-ignition prevention level only in a predetermined time. Those Time is preferably selected such that an emergency operating phase ensured long enough to be restarted before restarting Fire prevention or fire extinguishing an ignition or re-ignition of Materials in the protected area continue to prevent.

Fig. 3 shows a profile of the oxygen content in a protection area, wherein here the second alternative of the method according to the invention in the inerting process is implemented. As in the case of FIGS. 1 and 2, the ordinate axis represents here the oxygen content in the protected area and the abscissa axis is the time. As shown in FIG. 3, an oxygen concentration is initially within the scope of protection of 21% by volume present.

After a prophylactic Erstabsenkung a fire prevention system begins at time t ₀ , the oxygen content in the protection area is rapidly lowered to the control concentration RK. As shown, the oxygen concentration in the protection region reaches the re-ignition prevention level GK at time t ₁ and the control concentration RK at time t ₂ . The period from t ₀ to t ₂ is referred to as Erstabsenkung.

In order to prevent after the initial lowering, that in the protected area Materials can ignite, is also a directly to the Erstabsenkung subsequent fire protection phase provided for effective fire prevention. In In this phase, the oxygen concentration becomes within the protection range below the re-ignition prevention level or the limit concentration GK. Usually this is done by inert gas or oxygen from the primary source when needed displacing gas is introduced into the protected area to the oxygen concentration in the control range around the control concentration RK or below the Operating concentration BK.

In case of failure of the primary source is now provided according to the invention that the Ausfallssicherheitsabstand ASA between the limit concentration GK and the operating concentration BK is so large that the increase curve of the oxygen content is the limit concentration GK reaches z only in a given time, creating a sufficient Emergency operating phase is achieved.

For explanation, it should be noted that entered in Fig. 3, the neck which is shown to an enlarged extent in FIG.

Claims (10)

An inerting method for reducing the risk of fire in an enclosed protected area, wherein the oxygen content in the protected area is maintained at a predeterminable control range by introducing an oxygen displacing gas from a primary source for a certain time to a control concentration (RK) below an operating concentration (BK) .
characterized in that
the control concentration (RK) is maintained in case of failure of the primary source for an emergency operation time by a secondary source. Inertization process according to claim 1,
characterized in that
the operating concentration (BK) is equal to or approximately equal to a design concentration (AK) specified for the protected area. Inertisierungsverfahren according to the preamble of claim 1,
characterized in that
the control concentration (RK) and the operating concentration (BK) are reduced so far below the design concentration (AK) specified for the protection area that the increase curve of the oxygen content in the event of failure of the primary source has a limit concentration (GK ) reached in a given time. Inertization process according to claim 3,
characterized in that
the failure safety distance (ASA) is determined taking into account a valid for the protection range air exchange rate, in particular a n ₅₀ - value of the protected area, and / or the pressure difference between the protected area and the environment. An inerting method according to claim 3 or 4,
characterized in that
the design concentration (AK) is lowered by a safety margin (S) below the limit concentration (GK) determined for the protection area. An inerting method according to any one of claims 2 to 5, comprising a detector for detecting a fire parameter,
characterized in that
the oxygen content in the protection zone upon detection of an incipient fire or a fire is rapidly reduced to the control concentration if the oxygen content was previously at a higher level. Inertization process according to one of the preceding claims,
characterized in that
the control range is about ± 0.2 vol.% oxygen content around the control concentration (RK). Inertization process according to one of the preceding claims,
characterized in that
the regulation of the oxygen content in the protected area taking into account the air exchange rate, in particular the n ₅₀ value of the protected area, and / or the pressure difference between the protected area and the surrounding area. Inertization process according to one of the preceding claims,
characterized in that
the calculation of the amount of extinguishing agent for maintaining the control concentration (RK) in the protected area taking into account the air exchange rate of the target area, in particular the n ₅₀ - value of the target area, and / or the pressure difference between the target area and the environment. Device for carrying out the method according to one or more of claims 1 to 9,
characterized in that
the primary source and / or the secondary source is an oxygen displacing gas generating machine, a bottle battery, a buffer volume, or an oxygen depriving or similar machine.

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