Method and apparatus for detecting and locating explosives, biological, and chemical substances in ducts and structures using tracers
A method and an apparatus for detecting, locating, and quantifying explosive materials and devices, and naturally occurring and man-made dangerous or hazardous biological and chemical materials and devices in ducts or piping systems, or other fluid flow systems in buildings such as residential, office, industrial, and power plants, transportation systems such as ships, airplanes, subways, and trains, and various types of infrastructure such as dams, tunnels, or bridges, and in the rooms, compartments, enclosures, containers, or difficult to access areas in these buildings, transportation systems, and structures. The preferred embodiment of this detection and location method uses a conservative tracer and one or more interactive tracers that are injected into the duct or area to be searched at one location and then monitored at the same or another location in the duct or area. Alternative embodiments, which are quicker and just as accurate for detection and location, require only the use of interactive tracers. Detection, location, and quantification are accomplished by analysis of the characteristic features of measured curves of tracer concentration. Various types of interactive tracers may be used, including partitioning and reactive tracer gaseous tracers.
1. A method for determining the location of a contaminant in an enclosed gaseous flow system within a structure, comprising the steps of:
(a) injecting a gaseous conservative tracer and a gaseous partitioning tracer into the gaseous flow system at a first location;
(b) advecting the tracers along the gaseous flow system at a first speed to create an advection flow field;
(c) extracting the tracers at a second location in the gaseous flow system;
(d) introducing a perturbation to the advection flow field at a perturbation time by changing and then re-establishing the advection flow at a second advection speed, which may be different than the first advection speed, creating a unique change in the concentration of the partitioning tracer;
(e) extracting the partitioning tracer as a function of time relative to the perturbation time;
(f) measuring the concentration of the partitioning tracer as a function of the time; and
(g) determining the location of contamination from the time of arrival of the partitioning tracer relative to the perturbation time and the advection flow speed.
2. The method of claim 1 wherein detection of the presence of a contaminant is determined from the presence of the interactive tracer that is being emitted from the contaminant after the tracers originally injected into the structure have been removed.
3. The method of claim 1 wherein the distance from the contaminant to the extraction point is determined from the time of arrival of the partitioning tracer after said advection flow field has been re-established.
4. The method of claim 3 wherein the mean time of arrival is determined from the first arrival of the tracer at the extraction point.
5. The method of claim 3 wherein the mean time of arrival is determined from the leading edge of the measured concentration curve at the extraction point.