THE TECHNOLOGY FOR DETECTING WEAPONS OF mass destruction (WMD) has been advancing each year since 1995, when sarin nerve agent was released in the Tokyo subway system; some of the most dramatic advances have been seen this past year. Although some of the newer devices represent a simple retooling of existing technologies, others represent substantial advances in technology. For a number of years, WMD detection specialists have had a desire to combine detection technologies into one device, because that is seen as the best method for obtaining accurate results. The basic operational philosophy is simple-while each technology may have known false positives, it is less likely that several different technologies will have false positives for the same material, thereby yielding a more accurate result.
A few years ago, there was a device that combined ion mobility spectrometry (IMS) and surface acoustical wave (SAW) sensors into one detection device. In theory, this was a good approach, but the device is no longer on the market. Any device that uses multiple technologies to detect chemical materials is on the right track.
MOST COMMON TECHNOLOGIES
As a review, the three most common technologies for detecting chemical warfare agents are IMS, SAW, and flame spectrophotometry. None of these technologies are very quick at identifying chemical warfare agents; they have detection times of 20 to 90 seconds. Each of these technologies has advantages and disadvantages (Table 1).
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Ion Mobility Spectrometry
The most common detection technology today is IMS, which typically uses a radiation source as its method of ionization. Although ionization is a common detection method, the mechanism that performs the ionization can vary. For example, a photoionization detector (PID) is a very common emergency response device and uses an ultraviolet lamp to ionize the chemical sample. Regardless of the technology, ionization is simply the process of changing the electrical activity within a molecule. In the case of the PID, the ultraviolet lamp ionizes the gas sample and makes it into an ion. The ion has an electrical makeup, since electrons and protons carry electrical charges. Within the PID sensor, there are two probes that monitor electrical activity, which is converted to a reading based on the calibration gas. The PID provides only a qualitative indication that a gas is present and, depending on the calibration and correction factors, may indicate the quantity of gas present. The PID cannot identify a gas or a mixture of gases; it indicates only the presence of a volatile material.
The IMS device also ionizes the gas sample and measures the time it takes for the various molecules to move down a sample tube. Most IMS devices use a Nickel-63 radiation source to perform this ionization. They also require an internal sieve that contains calibration materials. One of the major issues with this internal sieve is that it must go back to the factory for replacement.
 Photos by David Handschuh. |
There is also a new IMS device that uses a corona discharge. Once again, only the source of the ionization differs. One major advantage is that the Nickel-63 radiation source takes 20 to 90 seconds to identify a material, whereas the corona discharge can do it in five to 10 seconds. The device is small and can fit into the palm of the hand. It can detect the standard military chemical warfare agents as well as a suite of toxic industrial chemicals (TIC). The current TICs identified include hydrogen sulfide, hydrogen chloride, hydrogen fluoride, hydrogen bromide, chlorine, sulfur dioxide, phosgene, and hydrogen cyanide. Since it is IMS, other chemicals could be added to the library if the manufacturer develops the algorithms for the new materials. Detection levels are all below the immediately dangerous to life or health (IDLH) levels and in some cases 1/20 of the IDLH level. The exact detection threshold is dependent on environmental conditions. Major advantages of the new corona discharge units are that they can operate on four AA batteries and the sieve (calibration) pack is field replaceable. The list price for the corona discharge device is approximately $8,000; a sieve pack costs $45 each for a box of 10. The sieve pack has a typical lifetime of 250 to 300 hours of use.
Combination Sensor Device
The combination sensor device integrates multiple detection technologies. Three technologies-photoionization, IMS, and a suite of Taguchi gas sensors-are combined into one detection box. The IMS sensor is driven by corona discharge and is a nonradioactive technology. The Taguchi gas sensors are semiconductor sensors and have good reactions to volatile organic compounds and other flammable materials. There are six of these sensors in the device, and they have a good range for detecting a variety of materials in the air.
SAW DEVICE
A stand-alone SAW device, known for its accuracy, has multiple SAW sensors inside the detection device that work together to identify a gas. The multiple sensors provide the stand-alone SAW’s reliability in addition to two other detection technologies. The photoionization sensor, a good broad-range sensor, can detect a wide variety of volatile organic materials in the air, generally at low levels. With the suite of Taguchi sensors, some identifications can be made, depending on the sensors’ reactions. Combined with the capability of the IMS sensor, the device should be able to reduce false positives.
Several devices now in development will mimic this sensor suite. The key to this device’s success is integrating the software that drives the sensors. By establishing algorithms, you can identify a material by the individual sensor’s reaction. The software evaluates each of the three readings and makes a determination. At the low end, the device can establish that a material is present in the air. The device also may be able to identify the contaminant and provide a relative concentration. The list of TICs it can detect comes from the NATO International Task Force-25’s list of materials considered hazardous (Table 2). The chemicals are classified according to the level of toxicity: high, medium, and low hazard. Some of the chemical warfare agents, such as hydrogen cyanide, are also toxic industrial materials.
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The device has 25 chemicals listed in its library, which can be expanded to 50 TICs. The detection thresholds vary, but most are better than 1/10 of the IDLH level. All of the thresholds are within one-half to 1/40 of the IDLH levels. The device can detect most of the materials on the high and medium threat lists. The response time is quick, considering what the device has to accomplish. The PID reacts within a second, the IMS reacts within five seconds, and the Taguchi sensors react in milliseconds. The analysis takes 10 to 12 seconds. The cost of the device is $25,000, and the sieve pack ($45 for a pack of 10) is disposable.
BIOLOGICAL DETECTION
One detection device, which uses immunomagnetic sandwich assay technology, is available for biological agents. It can detect anthrax, ricin, botulism, plague, and SEB. It is easy to operate and can provide a yes or no answer in five minutes.
Most handheld assays use lateral flow immunoassay in which the threat agent, such as anthrax, binds with a fluorescent material coated with an antigen-specific (anthrax) antibody. The materials then move to a detection zone, where a reader determines if the fluorescent material is present. If so, the reading would be positive. It takes about 20 minutes to run a sample.
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Although the immunomagnetic sandwich assay adds a few more steps, it performs the testing in a shorter time. The sandwich assay has comparable fluorescent materials and a magnetic material. The threat agent (anthrax) is attracted to both of these materials. The target agent binds with the fluorescent material and the magnetic material. Once they are combined, making a sandwich, a magnetic field is applied, which attracts the sandwich containing the anthrax and the fluorescent material. A wash step is added to remove any other contaminants and the excess of fluorescent materials that did not bind.
The presence of fluorescent material in the sensing chamber indicates a positive test and the presence of anthrax. The device has been tested by three independent laboratories and has been found to work as stated by the manufacturer. The device has a detection threshold of <10,000 anthrax spores; however, in testing, the device detected lower levels and showed good consistency at 5,000 spores and lower. As with many devices, the lower the threshold for detection, the greater the chance of false positives. Conversely, the higher the threshold for detection, the lower the chance for false positives. In one test, there was an issue with false positives involving calcium; the manufacturer has since corrected that problem by changing the buffer solution.
The device costs less than $15,000; the cartridge costs approximately $25 per test. The device is comparable in operation to its lateral flow assay cousins and has similar steps in sample preparation. A small sample of the suspect material is placed in a sample container and mixed with a buffer solution. The sample cartridge is then placed in a reader for analysis. The testing process is relatively easy when wearing thin nitrile gloves but is somewhat cumbersome while wearing encapsulating chemical vapor (Level A) ensembles.
Although the number of new devices is low, their capabilities represent tremendous leaps in technology. At this time, the multiple sensor device has not been extensively street tested; its ultimate application will depend on its ability to maintain its success in the laboratory. It shows promise, and just the thought of integrating three technologies in one box is exciting. This is a giant step forward in chemical detection and has set the bar for future devices. A number of devices working on nanotechnologies (think very small) are in the early stages of development.
Using the devices that are available can improve our ability to detect chemical and biological threat agents. The biodetection device offers a good option for those who cannot afford a polymerase chain reaction (PCR) device, which has higher accuracy for biological threat agents. It offers quick answers and is an improvement over devices now on the market. The laboratory, specifically one in the Laboratory Response Network (LRN), continues to be the gold standard for biodetection. Samples should be collected according to law enforcement protocols and be sent to the laboratory for the final analysis.
These devices are tools in the responder’s tool box and are not the end all for detection devices. You should also use devices to identify risks such as fire and corrosive, toxic, and radioactive hazards, which are integral parts of a risk-based response philosophy.
CHRISTOPHER HAWLEY has served 24 years as a firefighter and 17 years as a hazmat responder. He is a deputy senior project manager in the National Security Programs Division of Computer Sciences Corporation (CSC), Alexandria, Virginia. He supports the Department of Defense International Counterproliferation Program (ICP) in course development, delivery, and client support. The ICP Program provides WMD courses and exercises throughout Eastern Europe, Central Asia, and many other parts of the world. Previously, Hawley served as a fire specialist and special operations coordinator for the Baltimore County (MD) Fire Department. In this capacity, he coordinated the hazardous materials response and advanced technical rescue teams. Hawley has had published five texts on hazardous materials and terrorism response, including one specifically on air monitoring and detection devices. He has written numerous magazine and trade journal articles and has assisted many publishers in reviewing and developing emergency services texts and publications.
