In today's world there is an awareness of the necessity of safeguarding the environment in which we live. Laws have been enacted and regulations promulgated to achieve a high ethic of responsibility for our environment. One problem faced by governments and individuals is the increasing incidence of leakage of toxic or hazardous substances from storage tanks into the soil and water supply. Detection of such leaks has become a priority. Early response to such releases can reduce the risks to human health and the enrivonment.
Several leak detection techniques are, at present, in use or have been proposed. Examples of existing devices and methods are those illustrated in several U.S. patents discussed hereinbelow. U.S. Pat. No. 3,995,472, entitled Detector System, to Murray, shows a liquid, vapor or gas detector in combination with an alarm system. The device uses a hose which deteriorates in the presence of the material to be detected. This renders the interior of the hose open to the atmosphere. Because the hose is subject to pressure from the pressurized storage system, pressure in the system decreases when the hose deteriorates. A pressure switch associated with the hose sets off an alarm. Since the hose is disposed beneath the tank to be monitored, the system of Murray is not extremely sensitive to fluids which may be emitted from the top or the sides of the tank into the surrounding soil. The Murray system additionally will not capture, in a container, any of the leaking substance. Also, the hose could deteriorate from naturally occurring substances within the soil because it is in constant contact with the soil and whatever acids or other corrosive substances may be present therein. In order to inspect or replace the hose after a period of time, the whole tank must be removed from the ground, which is an expensive operation.
Another device is shown in U.S. Pat. No. 4,125,822, entitled Probe for Determining Organic Liquids, to Perren, et al. This patent shows a detector comprising a rubber-like material which swells in response to the presence of an organic liquid to be detected. The detector comprises a plastic or rubber body which swells in contact with organic liquids such as mineral oil. The body contains conductive, fine, solid particles distributed therein so as to be in contact with each other. When sufficient contaminant enters the body, it swells, its electrical resistance increasing due to the swelling which moves the conductive particles apart. The inreased resistance is utilized in an external electrical circuit to set off an alarm.
Another prior art device, disclosed in U.S. Pat. No. 4,404,516, entitled System for Detecting Breaks from Liquid-Containing Reservoirs and Conduits, to Johnson, Jr., comprises a grid of electrically conductive wires which are placed directly under a tank, reservoir or conduit to be monitored for leakage and relies upon corrosion of the wires, alternatively, degradation of insulation around the wires, in response to exposure to the leaking substance. Wire or insulation corrosion causes a change in the electrical conductivity of the wires which is detected by electrically monitoring the wire grid. Because a grid is used, the location of the leak can be localized. This device is expensive to inspect or replace because the reservoir or conduit must first be removed to get to the electrical wire grid located beneath it.
U.S. Pat. No. 4,206,402, entitled System and Method for Detecting Leakage in a Pipeline or Tank, to Ishido, discloses a fluid leak detecting comprising a sensing coaxial cable permeable to oily fluids. The electrical carrying capacity of the coaxial cable changes upon penetration by the fluids and this change is detectable by monitoring an oscillating electrical signal from an external source. This device, too, is buried adjacent a pipeline or a tank and requires monitoring an external source of electrical signals. This and many other existing leak detectors require the input of an electrical signal from an outside soruce, when the source of the signal breaks down, the detectors cease to operate.
U.S. Pat. No. 3,961,900, entitled Combustible Vapor detector, to Gintelia shows a device for detecting the presence of combustible vapors in the air. An aluminum heat sink and a chamber through which samples of air are continuously drawn are utilized. Separate filaments that change in resistive value as a function of the presence of combustible gas in contact therewith are disposed within the chambers. Once again, continuously operating electrical circuitry is required as well as a filament burn-out detection circuit and an unbalanced wheatstone bridge, which goes through balance to a reverse unbalanced condition when a combustible vapor comes into contact with the sensing element.
U.S. Pat. No. 4,305,068, entitled Detector System, to Klein, shows a system for detecting leaks in tanks and pipelines. A sensor degradable on contact with the liquid, gas or vapor to be detected contains a fluid, the level of which is monitored by electrodes and an external electrical circuit. When the sensor body degrades, the fluid flows therefrom to reduce the fluid level and open the circuit between the electrodes to activate an alarm system.
As will be appreciated by those skilled in the art, none of these prior art systems offers a manner of collecting, for analyses, the triggering contaminant isolated from surrounding substances. Most of the above mentioned patents disclose detection systems which have to be continuously monitored and managed and frequently must be periodically inspected in order for the continuing integrity thereof to be assured. In many situations, an inspection requires the expensive and time-consuming removal of a tank or a pipeline, requiring extensive excavation, during which the monitor of detector would be inoperative or unreliable. None of these detectors are easily removable for examination or easily tested for operability and condition. Many of the detection systems disclosed hereinabove are expensive to fabricate and require surveillance by skilled personnel as well as expensive electrical apparatus. None of the prior art detectors is inexpensive to manufacture or easily inspected and replaced by unskilled people in the field.