Method and apparatus for continuously monitoring interstitial regions in gasoline storage facilities and pipelines

TECHNICAL FIELD [0001] The present invention relates generally to an apparatus and method for interstitial monitoring, and in particular a system for continuous monitoring of pressure and vacuum levels in the interstitial space of an underground storage tank system.

[0002] The current and proposed state of the art and state regulations require that underground storage tanks, used for storing hazardous substances, meet certain requirements relating to environmental safety. In particular, these environmental regulations require that underground storage systems contain a primary containment and secondary containment (see e.g. document DE 42 18 890 A1). In addition, the primary and secondary containment are required to meet environmental standards that require the underground storage tank systems to be product-tight. The term "product-tight", for the purposes of the environmental regulations mentioned above, is generally defined as impermeable to substances that are in the tank in order to prevent the substance from leaking out so that the tank undergoes physical or chemical degradation by the stored substance over the entire lifetime of the tank. Furthermore, these regulations require that the owners or operators of an underground storage tank system with a single-walled component located not more than 0.3 km (1000 feet) from the public water well of the main enclosure be sealed for safety. In addition, the product can not

Drinking water, used a program to detect or monitor larger spills.

[0003] One known leakage monitoring method, described in US Patent No. 6,489,894, entitled "Leak Detection Device for Double Wall Pipeline Systems and Container Systems", uses a pump leak detector vacuum, including a pressure-dependent switch and an alarm device for detecting leaks in a double walled pipeline or tank system. The described leak detector is adapted for simultaneous monitoring of several tanks connected to the main main line and to the vacuum pump by vacuum lines. Each monitored tank includes a vacuum connector or valve to fluidly connect the controlled space to the leak detector. Each vacuum line has a first fluid sluice, located in a vacuum connector, to block any fluid that has leaked into the vacuum lines from the leaking tank before entering leak-free tanks. A second fluid sluice is located in the collection main line to prevent fluid from entering the vacuum pump. Although this method can detect leaks within the controlled space of the tank, it is a mechanically complex system that requires the use of large amounts of materials and a lot of time during installation.

[0004] Other methods for monitoring the interior of a secondary or interstitial space are well known in the art and include continuous leak detection using both pressure and brine monitoring techniques to determine the presence or absence of leakage between the storage system and the surrounding environment. However, in order to successfully calibrate all these known methods and systems for operation, a lot of configuration time is required

And system knowledge. In particular, in order to configure said monitoring systems for operation, the user must enter the volume of the secondary or interstitial space to be monitored, which requires detailed knowledge about the arrangement and configuration of the double wall pipeline and tanks used in the underground storage system.

SUMMARY OF THE INVENTION [0005] An underground storage system includes a primary containment and secondary containment adapted to the sealed environment of the primary containment. The underground storage system further includes a leak detection system that is in fluid communication with the secondary containment system and which is adapted to detect fluid leaks in the primary containment system and the secondary containment system.

BRIEF DESCRIPTION OF THE DRAWINGS [0006] For a more complete understanding of the device being described, reference should be made to the following detailed description and accompanying drawings in which:

[0007] Fig. 1 illustrates the basic components of an exemplary interstitial vacuum monitoring system.

[0008] Fig. 2 illustrates a flowchart showing in detail the operation of an exemplary self-learning procedure; [0009] Fig. 3 illustrates an exemplary interstitial vacuum curve; and [0010] Fig. 4 illustrates a flowchart showing in detail the operation of an exemplary monitoring procedure.

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DETAILED DESCRIPTION [0011] Fig. 1 illustrates an exemplary underground storage system 10 that includes an underground storage tank (UST) 12, designed to securely store fluid 20, for example gasoline, diesel or other hydrocarbon. The UST 12 tank is a double-walled storage tank, comprising the outer wall 14 and the inner wall 16, separated to form interstitial space 18. In this way, the UST 12 tank is divided into a main safety enclosure and a secondary safety enclosure to provide redundant leakage protection to the underground storage system 10.

[0012] A submersible pump (STP) 22, such as the STP model number STP-75-VL2-7, manufactured by FE PETRO, INC.®, provides a means for pumping fluid 20 into the dispenser 24. The STP 22 pump can be mounted permanently or removably to the UST tank 12 to position the inlet nozzle 22a below the fluid surface 20. The inlet nozzle 22a in turn provides a flow path for pumping fluid 20 within the main containment housing to the dispenser 24.

[0013] The pump manifold 26, which may be an integral part of the STP pump 22, or a separate component permanently attached thereto, controls the distribution of pumped fluid 20 to the dispenser 24. The manifold pump pipe 26 includes a siphon port 28 adapted to flow interstitial space connection 18 (e.g. secondary safety enclosure) with the vacuum generated by the STP pump 22. Thus, when the STP pump 22 is turned on (e.g. creates a vacuum), the siphon port 28 provides a vacuum path to the interstitial space 18 in order to draw out the liquid it contains. The control valve 30 can isolate the interstitial space 18 from the siphon port 28 to prevent a fall

Vacuum when the STP 22 pump is not turned on and is subjected to atmospheric pressure through the main safety housing.

[0014] The vacuum sensor 32 fluidly connects to the interstitial space 18 and the siphon port 28 to sample and measure the vacuum level within it. The vacuum sensor 32 may be a continuous analog sensor, a discrete digital sensor, a switch-based sensor, or any other device adapted to sample the vacuum level in interstitial space 18. Vacuum sensor 32 can be isolated by control valve 30 to prevent atmospheric pressure measurements (i.e., zero vacuum measurements) when the STP pump 22 is turned off. However, when the STP pump 22 is turned on and creates a vacuum, the control valve 30 opens to provide a fluid connection between the vacuum sensor 32, the interstitial space 18 and the siphon port 28. In this way, the vacuum sensor 32 samples and measures changes in the vacuum level within the interstitial space 18 produced by the STP pump 22.

[0015] In addition, the vacuum sensor 32 may be communicatively connected to a control unit 34, comprising a processor 36 and a memory 38. The control unit 34 and a memory 38 receive and store vacuum data, system information, alarm data, etc. from the vacuum sensor 32 or any other another controlled component. Communication between control unit 34 and, for example, vacuum sensor 32 and control valve 30 can be accomplished using any desired communication link, such as a wired local area network, wireless communication link, direct communication link, or point-to-point communication link .

[0016] The processor 36 may perform a control procedure to direct the configuration and operation of the underground storage system 10. In particular, procedures

53 / 59P31528EN00 can be written in any process control programming language or in a computer language such as C⁺⁺, Visual C⁺⁺, Visual Basic, in machine language and can be compiled (if necessary) and stored in memory 38. Basically, the control procedure ensures the integrity of the underground storage system 10 by detecting unwanted leaks. In particular, the control procedure may be performed on the processor 36 to automatically learn the vacuum characteristics of the interstitial space 18. In addition, control procedures may include additional subroutines, adapted to be performed on processor 36, to continuously monitor vacuum level in interstitial space 18 as a function of time.

[0017] Leak outlet valve 40 fluidly combines control valve 30, vacuum sensor 32 and leak outlet 42 to provide a vacuum path to interstitial space 18. Leak outlet valve 40 and leak outlet 42 can form a removable assembly adapted to be detached from the space interstitial storage configuration.

is already needed for the system 10 underground leakage 40 enables

18 when not and actions

Discharge valve automatic or manual generation of calibrated or controlled leakage between interstitial space 18 and atmospheric pressure outside the leakage outlet 42. Such controlled leakage reduces the vacuum level in the interstitial space.

[0018] Vacuum sensor 32 may in turn measure the decreasing vacuum level and send the vacuum level data via a communication link to the control procedure performed in the control unit 34. The control procedure may in turn process vacuum level data to determine one or more characteristics of the vacuum in the interstitial space 18. In particular, the control procedure may determine a negative rate of vacuum level change based on decreasing data

In particular, the system components 10 vacuum space calibration procedure vacuum level, resulting from the introduction of controlled leakage into the secondary safety enclosure. It should be noted that other vacuum characteristics, such as, for example, positive rate of vacuum level change, or time to completely empty the interstitial space, can additionally or alternatively be determined based on vacuum level data.

[0019] The UST tank 12 can be combined with other underground storage. The interstitial 18 can be fluidly connected to the secondary interstitial space 48 of the dispenser pipe 46 through a plurality of vacuum ports 44-44b. In operation, the double-walled dispenser tube 46 can provide a fluid connection between fluid 20 stored in the UST tank 22 and dispenser 24. Thus, the entire underground storage system 10, including the UST 12 tank and dispenser pipe 46, is double-walled and product-tight, preventing penetration and corrosion that may occur during normal operation.

[0020] Fig. 2 illustrates a generalized flowchart of an autocalibrating or self-learning sub-procedure 50 adapted to learn the characteristics of a vacuum in interstitial space 18. The self-learning sub-procedure 50 determines and maintains the characteristics of a vacuum partly based on measured changes in vacuum level as a function of time. The self-learning procedure 50 learns the characteristics of the vacuum without having to determine or calculate the total volume of interstitial space 18, vacuum performance of the STP pump 22, the sensitivity of the vacuum sensor 32 etc. In this way, the self-learning 50 provides a fast and effective means for monitoring the space between 18 of any known or unknown volume or complexity. It should be noted that the self-learning procedure 50 can operate as an autonomous procedure, independent of the control procedure or other subroutines. However, self-learning procedure 50 can

53 / 59P31528EN00 be integrated into the control procedure to meet the calibration requirements of the underground storage system. [0021] The self-learning procedure 50 may be performed when a particular criterion is met. In particular, self-learning procedure 50 may be performed manually as part of a regular maintenance procedure, or automatically, in response to changes in the configuration of the underground storage system 10, as part of the initial setup and configuration of the underground storage system 10, or to compensate for level changes vacuum in time.

[0022] Block 52 retrieves from the memory 38 the saved initial settings and default conditions required to perform the self-learning procedure 50 (see Fig. 1). Said initial settings and default conditions may include, but are not limited to, the maximum desired vacuum level Pmax, the minimum permissible vacuum level Pmin, closing of the control valve 30 and calibration of the vacuum sensor 32.

[0023] Although the maximum desired vacuum level can be virtually set to any value, experimental studies indicate that a vacuum level of approximately 10 inches Hg (254 mm Hg) may be desired, which represents an achievable vacuum level that is easy to obtain distinguish from atmospheric pressure. Similarly, a minimum allowable vacuum level can be set to, for example, 2 inches Hg (50.8 mm Hg). Typically, the minimum vacuum Pmin level provides a lower limit or threshold value to identify when the current vacuum level, Pmeas, in interstitial space 18 decreases towards atmospheric pressure (i.e., approximately 0 inches Hg or zero vacuum).

[0024] At block 54, the vacuum sensor 32 samples and measures the current vacuum level Pmeas in the interstitial space 18.

Typically, the vacuum sensor 32 samples the current level of Pmeas vacuum at regular intervals At during self-learning operation

The procedure 38 may store vacuum level data representing the current vacuum level Pmax in a historical database as a stored vacuum level Pstored. The saved Pstored vacuum level can be permanently archived in a historical database (i.e. saved in a database), or can be temporarily saved for use in calculations, analyzes, etc., and then deleted or overwritten when new data is downloaded and preserved.

[0025] Block 56 compares the current vacuum level Pmeas with atmospheric pressure (i.e. zero vacuum) to determine the base vacuum before performing the remaining steps of the self-learning procedure 50. After detecting the vacuum in interstitial space 18, in block 58 the control valve 30 and the valve the discharge outlet is opened and provides the outlet of the detected vacuum to the atmosphere. At block 60, the vacuum sensor 32 samples the current vacuum level Pmeas until atmospheric pressure is detected. When the vacuum sensor 32 detects atmospheric pressure, in block 62 the control valve 30 and the discharge outlet valve 40 are closed to seal and isolate the interstitial space 18 in preparation for performing the emptying procedure as part of the self-learning procedure 50.

[0026] In block 64, an emptying procedure is initiated and the self-learning procedure 50 begins to learn the vacuum level data required to perform the "rising curve" (an example of which is shown in Fig. 3 in the form of line 102). In particular, in block 64 the STP pump 22 is switched on, which in turn starts emptying the interstitial space 18 through the siphon port 28. In block 66, the control valve 30 is opened to establish a flow connection between the STP pump 22, interstitial space 18 and the vacuum sensor 32. Usually, the control valve 30 opens with a delay equal to the time it takes for the vacuum sensor 32 to detect the vacuum generated by the pump

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STP 22. It should be noted that the delay associated with the vacuum sensor may further depend on factors such as the sensitivity of the vacuum sensor 32, the vacuum performance of the STP pump 22, and the total volume of interstitial space 18.

[0027] At block 68, the vacuum sensor 32 samples and measures the current vacuum level Pmeas in the interstitial space 18 during the time interval At. In block 70, processor 36 sets the stored vacuum Pstored level equal to the current vacuum Pmeas level and stores the resulting saved vacuum Pstored level in a historical database created in memory 38. At this point, the evacuation rate, or rate of change of the vacuum level of the rising curve in interstitial space 18 can be calculated based on the difference between the current vacuum level and the preserved vacuum level over a constant or known time interval. The rate of change of AP emptying_evac can be mathematically described by the formula:

AP "

P -P meas_stored

at

The rate of change of AP emptying_evac describes the positive or increasing slope of the emptying curve, representing an increase in vacuum level in the interstitial space 18. Alternatively, an emptying curve can be obtained by plotting the value of the current vacuum level Pmeas and the stored vacuum level Pstored, sampled during the operation of the self-learning subroutine 50 as a function of time.

[0028] In block 72, the current vacuum Pmeas level is compared to the maximum desired vacuum Pmax. If the current vacuum level is less than the maximum desired vacuum level, the self-learning procedure 50 enters loop 74 and continues sampling and maintaining the current vacuum level Pmeas until the maximum desired vacuum level is reached. However, when in block 72 it is detected that

The current vacuum level exceeds the maximum desired vacuum level, in block 76 the control valve 30 is closed.

[0029] Then, at block 78, the STP pump 22 is turned off and the draining procedure ends. At this point, interstitial space 18 is sealed and isolated by control valve 30 and the current vacuum level Pmeas remains substantially constant and at the maximum desired vacuum level Pmax.

[0030] At block 80, the vacuum sensor 32 samples and measures the current vacuum level Pmeas in the tight interstitial space 18 at each time interval At. The current vacuum Pmeas level should remain at the maximum desired vacuum Pmax for a specified number of time intervals. In addition, memory 38 may store the current vacuum level Pmeas, which is equal to the maximum desired vacuum level Pmax in the memory 38, as the stored vacuum level Pstored. At this point, the rate of change in vacuum level in interstitial space 18 is essentially zero. In other words, the vacuum level in the tight interstitial space is constant. A positive or negative change in the vacuum level during this time interval represents anomalies, such as leakage, that trigger an alarm. The rate of change of the maximum vacuum AP_maxcan be described mathematically by the formula:

P -P meas stored

AP

at

The rate of change of APmax of maximum vacuum is represented by a line with a zero slope corresponding to the maximum desired level of vacuum Pmax. It should be noted that setting the rate of change of the maximum vacuum level APmax is an optional calculation that can be performed by the control unit 34.

[0031] In block 82, the decay procedure is initiated and the self-learning procedure 50 begins to learn the level data

The vacuum required to generate a "falling curve" or "decay curve" (an example thereof is shown in Fig. 3 in the form of line 106). In particular, the discharge outlet valve 40 is opened in response to a command given by the control procedure performed in the control unit 34. During operation, the discharge outlet valve 40, which may be a manual valve that requires operator intervention to open it, provides a fluid flow path between the current vacuum level Pmeas in interstitial space 18 and the zero vacuum level in the atmosphere. In other words, the discharge outlet valve 40 provides an equalizing path between the high vacuum level in interstitial space 18 and the zero vacuum level at atmospheric pressure. The reduction of the current vacuum level Pmeas in interstitial space 18, caused by controlled leakage, provides a way to characterize the operation of the secondary containment in the presence of real, uncontrolled leakage.

[0032] At block 84, the vacuum sensor 32 samples and measures the decreasing current vacuum level Pmeas in the interstitial space 18 at each of the time intervals At. At block 86, the processor 36 stores the decreasing current vacuum level Pmeas in memory 38 as the stored level Pstored vacuum. At this point, the rate of change of the falling or disappearing vacuum level curve in interstitial space 18 can be calculated based on the difference between the stored vacuum level Pstored and the current level P_meas vacuum in a specified period of time At. The rate of change of AP_decay decay can be mathematically described by the formula:

P -P stored meas

AP decay

at

The rate of change of APdecay decay represents the negative slope of the decay curve, which is the line formed by the decreasing values ​​of the current vacuum level Pmeas, measured by

53 / 59P31528EN00 vacuum sensor 32 during the disappearance procedure of the self-learning procedure 50.

[0033] In block 88, the current vacuum Pmeas level is compared to the minimum desired vacuum Pmin level. It should be noted that the minimum desired vacuum Pmin level can be set to zero vacuum (i.e., atmospheric pressure), but is usually set to a higher level to reduce the overall system setup time. In other words, the closer to the atmospheric pressure the minimum desired Pmin level of vacuum is set, the longer it takes to align the interstitial space 18. If the current vacuum level Pmeas is greater than the minimum desired vacuum level Pmin, the self-learning procedure 50 enters loop 90 and continues sampling and maintaining the current vacuum level Pmeas until the vacuum sensor 32 detects the minimum desired vacuum level Pmin in the interstitial space 18. However, if in block 88 the current vacuum level Pmeas is less than the minimum desired vacuum level Pmin, in block 92 the control valve 30 is closed. At this point, the decay procedure in self-learning procedure 50 is completed and the learned rates of change APevac and APdecay can be combined to obtain the total vacuum characteristic curve shown in Fig. 3.

[0034] Fig. 3 illustrates an exemplary overall vacuum curve 100, indicating the learned APevac and APdecay change rates and the optionally determined APmax, measured and determined as a result of the autocalibration procedure. As mentioned earlier, line 102 represents the learned rate of APevac emptying change obtained during self-learning procedure 50 and, in particular, illustrates the increase in vacuum level in interstitial space 18 as a function of time. Physically, line 102 represents a sealed interstitial space 18, in fluid communication, via a control valve 30, with an active STP pump 22. The maximum time Tmax represents the time it takes for the STP pump 22 to increase its current level

The vacuum in the interstitial space 18 to the maximum desired vacuum level Pmax.

[0035] The upper range defined by line 102a and the lower range defined by line 102b set the allowable amount of variation in the level of vacuum from line 102 known during the emptying procedure. The alarm subroutine can be activated when the current vacuum level Pmeas exceeds the allowable limits set by the upper and lower ranges defined by lines 102a and 102b. For example, the alarm subroutine may determine that there is leakage in interstitial space 18 when the current vacuum level is outside the upper and lower ranges defined by lines 102a and 102b, or when the maximum desired vacuum Pmax will not be obtained after Tmax.

[0036] Line 104 represents the maximum desired vacuum Pmax level and the known maximum vacuum rate of change AP_max equal to zero (i.e. the vacuum is constant). Physically, line 104 represents a constant current vacuum level, measured when interstitial space 18 is sealed and isolated from STP pump 22 and leak outlet valve 40. The isolated interstitial space 18 ensures that the current vacuum level Pmeas remains virtually constant, with a Pmax value for a specified number of time intervals.

[0037] As described earlier, line 106 represents the known decay change rate ΓΓ ^^ γ, determined during self-learning procedure 50. Line 106 illustrates the decrease in measured vacuum level in interstitial space 18 as a function of time. In particular, line 106 corresponds to the system configuration in which controlled leakage was introduced in the underground storage system 10 and the current vacuum level Pmeas decreases when the vacuum in interstitial space 18 equalizes with atmospheric pressure (i.e. zero vacuum level).

The drainage represents an airtight space. In other words, during monitoring in detail, [0038] As shown in Fig. 3, the drainage area 108 is defined by the top line 108a and bottom line 108b, deflected from line 106. Area 108 exemplary vacuum profile for interstitial 18 as a function of time.

normal operation (e.g. operation in stable conditions without leakage or other changes), the current vacuum level Pmeas should be in the area of ​​the steepness 108, defined by lines 108a and 108b. The unchanging loss of vacuum, represented by the drainage area 108, can be attributed to the natural drainage properties of the underground storage system 10 rather than leaks or other anomalies. However, if the current level is P_meas vacuum or AP change rate_curr_ent the current vacuum level extends beyond the area defined by lines 108a and 108b (i.e., extends beyond the wicking area 108), then it is assumed that leakage or other anomaly occurs within interstitial space 18 and an alarm subroutine can be started.

[0039] Fig. 4 is a flowchart showing the operation of an exemplary procedure 120 using the overall vacuum curve 100. At block 122, the vacuum sensor 32 samples and measures the current vacuum Pmeas level within the interstitial space 18. In block 124, the current vacuum Pmeas level is compared to the minimum allowable vacuum Pmin level (e.g., 51 mm (2 inches) Hg or zero vacuum). If the current vacuum level Pmeas is less than the permissible vacuum level Pmin, the STP pump 22 is turned on in block 126, which in turn starts emptying the interstitial space 17, as generally indicated by the emptying curve 102 shown in Fig. 3.

[0040] At block 128, the control valve 30 is opened, thus establishing a fluid connection between the STP pump 22, interstitial space 18 and the vacuum sensor 32.

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The control valve 30 is usually opened with a certain delay, equal to the time it takes for the vacuum sensor 32 to detect the vacuum generated by the STP pump 22. At block 130, the vacuum sensor 32 samples and measures the increasing current vacuum level Pmeas within the interstitial space 18 at each time interval at.

[0041] In block 132, the rate of change of the current APcurrent vacuum level is compared to the known rate of emptying change, APevac, determined during the self-learning procedure 50. It should be noted that the rate of change of the current APcurrent level of vacuum can be determined based on the difference between the current Pmeas level vacuum and stored levels Pstored vacuum as a function of time. The rate of APcurrent change of the current vacuum level can be described by the formula:

P -P meas stored

AP

[0042] If it is determined that the APcurrent change rate of the current vacuum level is less than the known APevac rate of emptying changes, an alarm procedure may be initiated in block 134. However, if the rate of change of the current APcurrent level of vacuum exceeds the known rate of change of APevac flushing, in block 136 the processor 36 retains the increasing current level of vacuum Pmeas in memory 38 as the stored level of vacuum Pstored.

[0043] with the current level the desired level enters the loop 140 and the current level Pmeas level P level P

In block 138, the current vacuum Pmeas level is compared with the maximum desired vacuum Pmeas level. If the vacuum Pmeas is less than the maximum vacuum Pmax, the monitoring procedure 120 continues sampling and maintaining the vacuum until the maximum desired vacuum is detected. However, if the current vacuum exceeds the maximum desired level Pmax of the vacuum, in block 142 the control valve 30 is closed.

[0044] In block 144, the STP pump 22 is turned off after the emptying of the now sealed interstitial space 18 is completed. Monitoring procedure 120 has therefore created a vacuum level within interstitial space 18. During operation, emptying or increasing the vacuum level in the interstitial space 18 continues along the known emptying curve 102 and the monitoring procedure 120 continuously verifies that the current vacuum level Pmeas remains within a predetermined range, determined by lines 102a and 102b. At the same time, the time needed to create in space between half the maximum desired vacuum level Pmax can be compared with the maximum time Tmax. If the current vacuum generation time exceeds the maximum time Tmax, a leak or other anomaly is assumed to be present and the alarm procedure 134 is initiated.

[0045] At block 146, monitoring procedure 120 is restarted such that at block 122 the vacuum sensor 32 samples and measures the current level of vacuum Pmeas. At block 124, the recently created current vacuum level Pmeas is compared to the minimum allowable vacuum level Pmin (e.g., 51 mm (2 inches) Hg or zero vacuum). Because the last created current Pmeas vacuum level is greater than the minimum allowable vacuum Pmin level, in block 148 the rate of change of the current vacuum level Pcurrent is compared with the known rate of change of AP_decay decay determined during self-learning procedure 50.

[0046] As discussed earlier, interstitial space 18 is airtight and monitoring procedure 120 measures the current vacuum level Pmeas, to determine if the decline in the current vacuum level Pmeas can be attributed to the natural leakage properties of the underground storage system, or leakage. In addition, a comparison between the known vacuum curve and the current vacuum Pmeas level can be based on the difference between the rate of AP change_decay disappearance and rate of change of AP_current

The current vacuum level or simply based on the difference between the current vacuum level Pmeas and the known vacuum curve itself.

[0047] At block 150, processor 36 maintains the current vacuum level Pmeas in memory 38 as the stored vacuum level Pstored. At this point, monitoring procedure 120 enters loop 152 and continues sampling and maintaining the current vacuum Pmeas level until the minimum permissible vacuum Pmin level is detected, at which point the STP pump is started to empty interstitial space 18. [0048] Similarly, monitoring the vacuum level during emptying can also be used to monitor problems. The system uses the known speed ΔPe_Vac evacuation or rising curve, shown as line 102 (Fig. 3), to determine if any fluid inflow has occurred to the secondary containment. This is accomplished by comparing the ascending curve in memory with the currently measured If the slope of the currently measured curve is greater than the slope of the known curve by a threshold factor, exceeding values ​​through line 102a (Fig. 3) (i.e. emptying the interstitial space takes less time than previously known), there is a suspicion that the fluid has entered the secondary containment. This is due to the fact that the influx of fluid enclosure space security

Furthermore, if the slope of the current ascending curve is smaller than the slope of the ascending curve by a threshold factor, exceeding the values ​​defined by lines 102b (Fig. 3) (i.e. emptying the interstitial space takes longer than it was known initially), then it is possible that there is a leak in vacuum suction line, allowing the influx of fluid. In each case (currently measured slope, respectively, the rising curve. ascendant is ascending indicated effectively reduced available for vacuum. measured known higher or correspondingly smaller than the known slope)

This will trigger an alarm. In this way, a physical fluid collection chamber and fluid sensor are not required, thereby reducing the cost and complexity of the system.

[0049] Although the embodiments described herein relate to measurements and analysis of the vacuum level, it should be noted that interstitial overpressure 18 can be used to provide a pressure gradient suitable for measurement by self-learning procedure 50 and monitoring by monitoring procedure 120. In addition, it should be noted that the current vacuum level Pmeas and the calculated rates of change can be determined manually. For example, manual commands may cause the control unit 34 to sample and maintain the current Pmeas vacuum level in interstitial space 18. In addition, the operator may use the change rates discussed above in conjunction with ideas and formulas regarding stored levels of Pstored vacuum to manually calculate desired change rates .

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