Multiple Leaks Research Articles

Endoscopic management of the liver transplant patient

Endoscopic management of the liver transplant patient

10 Times Epidural Blood Patches for Spontaneous Intracranial Hypotension -A case report-

This report describes the successful treatment of spontaneous intracranial hypotension (SIH) with multiple cerebrospinal fluid (CSF) leaks using 10 applications of epidural blood patches (EBP). A forty year old female who suffered with a postural headache was diagnosed as having SIH. On the cisternography, multiple CSF leaks were noted at the thoracic and lumbar area. Her headache was not improved with conservative treatments such as bed rest, hydration and NSAIDS. So, she underwent treatment with EBPs. After 10 applications of site-directed EBPs, her headache was resolved gradually and completely without any complications.

Leak location using the pattern of the frequency response diagram in pipelines: a numerical study

This paper presents a method of leak detection in a single pipe where the behaviour of the system frequency response diagram (FRD) is used as an indicator of the pipe integrity. The presence of a leak in a pipe imposes a pattern on the resonance peaks of the FRD that can be used as a clear indication of leakage. Analytical expressions describing the pattern of the resonance peaks are derived. Illustrations of how this pattern can be used to individually locate and size multiple leaks within the system are presented. Practical issues with the technique, such as the procedure for frequency response extraction, the impact of measurement position, noise- and frequency-dependent friction are also discussed.

The Performance of Electrical Methods for Assessing the Integrity of Geomembrane Liners in Landfill Caps and Waste Storage Ponds

Geomembrane leak location methods have been established based on injecting electrical current through the liner into the surrounding soil and then, using pairs of electrodes above the liner, high potential gradients associated with current leakage may be identified. Recently, permanent electrode arrays have been installed at a number of sites as a means of long term monitoring of the integrity of a landfill liner. There has, however, been no scientific study to date which addresses the performance of such systems. Here, we utilise a physical scale model of a landfill liner∕cap and investigate the usefulness of grid based and boundary electrode arrays for detecting multiple leaks in a landfill liner or cap. We compare the two electrode geometries under a series of controlled electrical leak experiments and demonstrate how both these arrangements can detect and locate leaks in a geomembrane. We also demonstrate some of the limitations of the method. For example, present data processing schemes can give misleading results when there are multiple leaks. The influence of variation in resistivity of the soil above or below the liner and also boundary current leakage on the performance of the technique is also studied. The results suggest that these two factors, unless they are accounted for, can have a significant impact on the results and subsequently affect the practical value of electrical leak detection systems.

Tubulation techniques for locating fine-leak sites in hermetic electronic packages

Bubble testing is often regarded, at best, as a poor method for locating gross leaks. However, it is demonstrated that, under proper conditions, bubble testing can be used to detect both gross and fine leaks, as well as their precise locations. Although not applicable in all situations, these leak-tests offer rapid and effective methods for identifying leak locations in components that are not adversely affected by the increased differential pressure. This method offers additional advantages such as not being fooled by virtual leaks, and indicating exact leak-location of single or multiple leaks in both the gross and fine leak regimes.

Radiologic Assessment of Spinal CSF Leakage in Spontaneous Intracranial Hypotension

Purpose : To assess the usefulness of imaging modalities in the detection of spinal CSF leakage in spontaneous intracranial hypotension. Materials and Methods : Fifteen patients who complained of postural headache without any preceding cause showed typical brain MR findings of intracranial hypotension, including radiologically confirmed CSF leakage. All fifteen underwent brain MRI and radionuclide cisternography. CT myelography was performed in eight patients and spinal MRI in six. Medical records, imaging findings and the incidence of spinal CSF leakage dur-ing each modality were retrospectively reviewed. Results : CSF leakage was most common at the cervicothoracic junction, where in seven of 15 cases it was seen on radionuclide cisternography as increased focal paraspinal activity. Leakage was noted at the mid-tho-racic level in three patients, at the upper thoracic level in two, and at the cervical and lumbar levels in the re-maining two. In two patients multiple CSF leaks were noted, and in all, early radioactive accumulation in the bladder was visualized. CT myelography revealed extrathecal and paraspinal contrast leakage in three of eight patients, and among those who underwent spinal MRI, dural enhancement was observed at the site of CSF leakage in all six, abnormal CSF signal in the neural foramen in one, and epidural CSF collection in one. Conclusion : Radionuclide cisternography is a useful method for the detection of CSF leakage in spontaneous intracranial hypotension. CT myelography and spinal MRI help determine the precise location of leakage.

Pipe segment failure dependency analysis and system failure probability estimation

The present paper is mainly concerned with pipe-system failure probability estimation. For this purpose, a multiple component dependent failure (MCDF) model is introduced to deal with dependency among pipe-segment failures. The MCDF model is directly derived from load–strength interference analysis with the underlying notion that stochastic environment load brings about failure dependency. The influence of pipe-segment failure dependency on pipe-system failure probability is addressed and a modified system failure probability model is presented. It is also shown that, with regard to a pipe system, the multiple failures of pipe-segment leaks might lead to a pipe-system disabling leak or even to a break. The probability of a pipe-system disabling leak or break induced by the simultaneous failures of multiple segment leaks is estimated by means of the MCDF model. The estimation results indicate that pipe-system failure probability depends not only on the mean values of the respective segment-failure probability random variables, but also on other distribution parameters (e.g., the standard deviations) of them. Pipe-system failure probability estimated by means of the modified model is sometimes several times lower than that estimated by the conventional system failure probability model.

Surgical treatment of spontaneous spinal cerebrospinal fluid leaks.

Spontaneous spinal cerebrospinal fluid (CSF) leaks are an increasingly recognized cause of intracranial hypotension and may require neurosurgical intervention. In the present report the authors review their experience with the surgical management of spontaneous spinal CSF leaks. Between 1992 and 1997, 10 patients with spontaneous spinal CSF leaks and intracranial hypotension were treated surgically. The mean age of the seven women and three men was 42.3 years (range 22-61 years). Preoperative imaging showed a single meningeal diverticulum in two patients, a complex of diverticula in one patient, and a focal CSF leak alone in seven patients. Surgical exploration in these seven patients demonstrated meningeal diverticula in one patient; no clear source of CSF leakage could be identified in the remaining six patients. Treatment consisted of ligation of the diverticula or packing of the epidural space with muscle or Gelfoam. Multiple simultaneous spinal CSF leaks were identified in three patients. All patients experienced complete relief of their headaches postoperatively. There has been no recurrence of symptoms in any of the patients during a mean follow-up period of 19 months (range 3-58 months; 16 person-years of cumulative follow up). Complications consisted of transient intracranial hypertension in one patient and leg numbness in another patient. Although the disease is often self-limiting, surgical treatment has an important role in the management of spontaneous spinal CSF leaks. Surgery is effective in eliminating the headaches and the morbidity is generally low. Surgical exploration for a focal CSF leak, as demonstrated on radiographic studies, usually does not reveal a clear source of the leak. Some patients may have multiple simultaneous CSF leaks.

Leak Detection in Networks of Pipelines by the Generalized Likelihood Ratio Method

An efficient model-based method to detect, locate, and estimate leaks occurring in networks of pipelines is proposed in this paper. The method is applicable to networks carrying incompressible fluids. The proposed method is an adaptation of the generalized likelihood ratio test which utilizes flow and pressure measurements and a steady state model of the network. It not only can predict leaks and isolate the leaking branch but also can estimate the magnitude of leak and location along the branch. Modified serial compensation strategy is employed to detect multiple leaks. A simulation study of a large network demonstrates the efficacy of the method. Also a bench scale laboratory experiment is performed to corroborate the simulation study.

Fault detection of multiple biases or process leaks in linear steady state systems

A new method for detecting, identifying, and estimating gross errors in steady state processes is described in this paper. This method improves the GLR test and can be applied to all types of gross errors including leaks and biases.

Geophysical Surveys of Leaking Tailings Impoundments

Alcoa of Australia's bauxite treatment plant at Kwinana discharges alkaline liquor to impoundments constructed on Quaternary formations of the Perth Basin. Contaminated groundwater has been detected outside some of these impoundments. The impoundments are constructed with an impermeable basal clay layer overlain by a permeable, thin sand blanket. Wet tailings slurry is poured in, the fine residue fraction is dried and stacked higher than the dyke walls allowing access of tracked vehicles and geophysical equipment to the impoundments. Leakage is initially detected from monitoring bores placed outside the impoundments. Approximate leak locations can then be detected from water level lows in piezometers placed within the semi-confined aquifer of the sand blanket. The mise-a-la-masse technique uses current electrodes placed within the impoundment and within conductive, leaking water at some distance away. A current pathway is provided between the impoundment and the conductive groundwater via the leakage zone and this can be mapped as voltage highs using potential electrodes within piezometer holes near the base of the impoundment. In some cases the detection of these leakage points is complicated, but not impossible, by multiple leaks, PVC liners placed above the basal clay layer and the strongly varying conductivity within the impoundment. The mise-a-la-masse anomalies only give leak location with differences in intensity between anomalies not being diagnostic of leak properties.

Characteristics of face seal leakage in filtering facepieces.

Several studies have found that aerosol size, testing method, leak size, leak position, sampling probe location, and the mixing condition inside the respirator affect the results of fit factor measurements. This study focuses on the effect of leak shape and filter resistance because leaks have been reported to vary in shape from circular to slit-like. Four leaks of different shape but the same cross-sectional area were used to study their effect on aerosol penetration. Dust-mist and high-efficiency particulate air filtering facepieces provided different filter resistances. An aerodynamic particle sizer and a laser aerosol spectrometer were used to measure the particle size-dependent aerosol concentrations inside and outside the respirators. The filtering facepieces were sealed to a mannequin and artificial leaks were inserted near the right cheek. Aerosol penetration was measured for five flow rates ranging from 5 to 100 L/min. The pressure drop across the mask was monitored with an inclined manometer. At a given pressure differential, a slit-like leak and multiple circular leaks have been found to pass less aerosols than a single circular leak of equal cross-sectional area because the leak flow decreases with an increase in leak shape complexity. If there is substantial lack of face seal fit and the breathing rate is low, a HEPA respirator may provide less protection than a dust-mist respirator because the pressure drop is considerably higher for a HEPA respirator, resulting in more aerosol flow through the leak.

LASER TREATMENT OF ECCENTRIC LEAKS IN CENTRAL SEROUS CHORIORETINOPATHY RESULTING IN DISAPPEARANCE OF UNTREATED JUXTAFOVEAL LEAKS

In central serous chorioretinopathy (CSCR) laser treatment of leaking points close to the macular center should be avoided because of the possibility of producing juxtafoveal scotoma and stimulating choroidal neovascularization. Nine eyes of nine consecutive patients with CSCR had two or more leaking points within a macular detachment, one of which was foveal or near to the fovea. Photocoagulation with green argon laser was performed in all eyes, treating all the leaking points except for the central one. Visual symptoms regressed after treatment, and the serous detachment was resolved 10 days to 4 weeks after photocoagulation in all cases. Fluorescein angiography showed no leakage at either the central leakage point or the leakage point that had been treated. These results led us to believe that the central or dependent leak in our cases was not sufficient to maintain the serous detachment by itself. An alternative hypothesis is that the untreated leak did not represent real fluid movement but only diffusion of fluorescein molecules, or a false leak. In cases of CSCR with multiple leaks within a single macular detachment, we believe that a foveal leak may be a dependent or false leak and that direct treatment is not necessary.

Distribution of Faceseal Leak Sites on a Half-Mask Respirator and Their Association with Facial Dimensions

Faceseal leaks on one brand of half-mask respirator worn by 73 human subjects were identified by deposition of a fluorescent tracer aerosol during a standard quantitative fit test. The identified leaks were categorized according to their location and shape. It was found that about 89% of all observed leaks occurred at the nose or chin or were multiple leaks which included these sites. Fit factors for these types of leaks were significantly lower than for other types of leaks. About 73% of all leaks approximated the shape of a slit rather than a round orifice, and the prevalence of these leaks was affected by gender. Significant association of facial dimensions and leak sites were found. Most of these were attributed to differences in gender, and only a very small percentage were for the facial dimensions used to define the Los Alamos respirator test panel. Significant correlation of facial dimensions and fit factor were found for only three facial dimensions; none of which are used to define the test panel. Evidence of airflow streamlining within the facepiece was observed on 22% of the subjects. Results of this study indicate that respirator leakage is strongly affected by nose and chin leaks, that gender is a factor in how a respirator fits, and that consideration should be given to including nasal dimensions when defining a respirator test panel and selecting a respirator for an individual wearer.

Distribution of Faceseal Leak Sites on a Half-Mask Respirator and Their Association with Facial Dimensions

Faceseal leaks on one brand of half-mask respirator worn by 73 human subjects were identified by deposition of a fluorescent tracer aerosol during a standard quantitative fit test. The identified leaks were categorized according to their location and shape. It was found that about 89% of all observed leaks occurred at the nose or chin or were multiple leaks which included these sites. Fit factors for these types of leaks were significantly lower than for other types of leaks. About 73% of all leaks approximated the shape of a slit rather than a round orifice, and the prevalence of these leaks was affected by gender. Significant association of facial dimensions and leak sites were found. Most of these were attributed to differences in gender, and only a very small percentage were for the facial dimensions used to define the Los Alamos respirator test panel. Significant correlation of facial dimensions and fit factor were found for only three facial dimensions; none of which are used to define the test panel. Evidence of airflow streamlining within the facepiece was observed on 22% of the subjects. Results of this study indicate that respirator leakage is strongly affected by nose and chin leaks, that gender is a factor in how a respirator fits, and that consideration should be given to including nasal dimensions when defining a respirator test panel and selecting a respirator for an individual wearer.

Model studies of electrical leak detection surveys in geomembrane‐lined impoundments

Pole‐dipole array electrical potential distributions are calculated for a geomembrane‐lined liquid impoundment having single or multiple leaks. A three‐dimensional numerical model is employed to represent a small circular leak in the highly resistive plastic liner. The liquid waste material, the liner, and the soil under the impoundment are simulated by infinite horizontal layers, with approximate corrections for the finite size of the impoundment. Parametric curves for a single leak show that with optimum selection of electrode spacing and positioning and other field survey parameters, leaks can be detected effectively. To identify and resolve the presence of a cluster of leaks, the potential measurements must be made close to the liner and the detector dipole spacing must be smaller than the separation of the leaks. The results also indicate that the survey speed may be increased when portable leak detection equipment employing a vertical dipole detector is used.

Electrical response of a leak in a geomembrane liner

A leak in a geomembrane lined impoundment or landfill has a characteristic electrical response. I simulate the waste material, the liner, and the soil under the liner by infinite horizontal layers and express the secondary potential for a leak in the geomembrane liner in terms of a three‐layer medium Green’s function and the unknown current density distribution at the leak. The area of the leak is sufficiently small for the leak current density to be essentially uniform. I add the primary potential associated with a leak‐free liner to the secondary potential to form an integral equation and derive a general expression for the current density at the boundary between the waste material and the liner. From the expression for the current density, I determine the current flow through the leak by assuming that the total current distribution flows vertically across a finite region of the infinite, thin liner layer. This finite region has the same surface area as does the waste disposal site or landfill. My analysis implies that the current density is the most sensitive variable affecting the magnitude of current flow through the leak and the amplitude of the leak anomaly response. Multiple circular leaks in the thin resistive liner are included in the analysis. The potential anomaly of a leak is a localized response which is capable of providing a useful means for detecting and locating such leaks accurately in large waste disposal sites or landfills. Excellent agreement between experimental and model data shows my general solution is accurate in predicting leak signatures and suggests the solution may be useful to model field data acquired in geomembrane lined impoundments or landfills.

City Had No Duty to Supply Noncorrosive Water

When Brynnwood Condominium I Association Inc. discovered multiple leaks in the copper tubing of its plumbing system, it claimed that the city of Clearwater furnished water containing high levels of chemicals that caused excessive corrosion in the pipes and increased copper concentrations in the tap water. A Florida appellate court ruled that it would be unreasonable to require the city to infuse the water with elements that would lessen damage to pipes.

Anomalies in the Measurement of Wetting Liquid Pressure Gradients

The purpose of this note is to call attention to a source of difficultywhich can be responsible for inaccurate estimates of wetting liquid pressuregradients in mixture flow experiments of the Hassler type. It has been ourexperience occasionally to observe what were indicated to be negative pressuregradients, and these were regarded as anomalous in the sense that physicallythey seemed to contradict the requirement that the flux be in the direction ofthe potential field. At first it was thought that our scheme of assembling barriers and coresample led to such asymmetry in the distribution of isobars that the manometricleads at each end of the core were responding to internal pressures (within thecore sample) which could be either positive or negative with respect to eachother, and which in fact might tend to reflect on different effective corelengths in an unpredictable fashion as the wetting liquid saturation waschanged. However, no compelling evidence of this possibility has beenestablished. In addition, we were cognizant of the requirements to be satisfiedin selecting manometric instrumentation to minimize the delay in response ofthe manometer to the differential pressures being measured, and were thusassured that our observations of anomalous pressure gradients could not beexplained by faulty instrumentation. What we suggest is that if a leak sink occurs in the fluid lines connecting thecore to either side of the differential manometer, errors exceeding 100 percent may result in the estimation of wetting liquid pressure gradient, eventhough the leak is of such small magnitude that its existence would tend to beobscured by evaporation effects. This is because in a system with leaks at thespecified places, the manometer records at steady state the pressure dropacross the manometer barrier elements in addition to the pressure drop acrossthe core sample. This possibility will be illustrated below analytically and by numericalexample for the special case where the leak occurs on the high pressure side ofthe core, since we are especially desirous to explain the significance of ourobservations of the so-called negative pressure gradients. It will beindicated, however, that leak sinks on the low pressure side of the core canaccount for observations of anomalously high values of pressure gradient, andthat multiple leaks on both sides of the core can provide for some compensationso that the errors in pressure estimation are reduced. However, the major pointto be emphasized is the fact that the impracticality of detecting the smallleak sinks which give rise to the difficulties makes it a complicated task forthe experimenter in a particular case to know with certainty that hisestimation of pressure gradient lies within the limits of error which can betolerated. T.N. 57