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This article was Originally Published on Jan 27, 2006 in Volume: 10  Issue: 1

Hunters of Chemical and Biological Threats

Sensor detection advances at a geometric pace.

By Patrick E. Clarke

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The pupil will constrict when a light is shone into the eye. This is called miosis. Strong emotion and certain drugs can also cause the pupil to constrict. The most frightening example of miosis can occur on the battlefield. It is the first physical symptom that someone has been exposed to a nerve agent.

Fortunately, both the private and public sector are working together to put more tools in the hands of the warfighter.

Industry Meeting the Need

Because the problems of chemical and biological threats are not limited to a single country, the response from industry has been equally worldwide.

A prime example is Proengin, well-known for its flame spectrometry equipment which ranges from handheld devices to fix bio detection systems. Most notably of Proengins’ detectors is the AP2C handheld chemical warfare (CW) agent detector which detects most CW agents, even degraded and homemade agents. However, until now you had to choose between CW agents (AP2C detector) or industrial compounds (toxic industrial materials (TIMS) detector).

In 2006 Proengin is releasing the AP4C which combines the detection capabilities of the AP2C and the TIMs into one unit. Now whether it’s responding to a terrorist attack or a roadside chemical spill, the AP4C is a single-use device capable of detecting a full spectrum of threats. Using flame spectroscopy, the AP4C is able to detect a wide range of chemicals to include 49 of 58 chemicals on NATO’s toxic industrial chemical (TIC)/TIM list whilst avoiding common false positives such as wintergreen. The AP4C is available in the UC kit including the S4PE liquid sampler.

Another example, General Dynamics Armament and Technical Products, headquartered in Charlotte, NC, is developing sophisticated detectors that will enable U.S. troops to be hunters of chemical/biological threats rather than prey.

The newest detector developed by General Dynamics is the JUNO handheld chemical agent detector, according to Janet Guertin, director, business development for detection systems. JUNO is capable of detecting, identifying, quantifying and alerting the user to the presence of chemical agent vapors significantly below the joint services operation requirement level. When used with an optional preconcentrator and communications/concentration cradle, JUNO will detect at miosis levels.

General Dynamics has long been one of the leading companies involved in sensor detection technology. “We produce the M-21 Automatic Chemical Agent Alarm, the first fielded standoff chemical detector and predecessor to the Joint Service Lightweight Standoff Chemical Agent Detector (JSLSCAD),” said Dan’l Thomas, program manager for standoff chemical detection programs.

The M21 alarm detects nerve and blister agent vapor clouds at line-of-sight distances out to five kilometers. It operates from a stationary mode and is intended for use on either a tripod or in conjunction with the FOX NBC reconnaissance vehicle. “M21s are currently in the field and are being used to protect coalition forces in Iraq and Afghanistan,” said Thomas. Standoff detectors can be used for detection from as far away as five kilometers, while point detectors only provide remote detection when used in conjunction with networks and unmanned vehicle systems. The JSLSCAD analyzes infrared light emitted or absorbed by a chemical cloud and identifies the presence of agents in the cloud by comparing its spectral signature.

The signatures are typically acquired in a laboratory with the actual agent, according to Dr. Alan C. Samuels, a research chemist on the passive standoff detection team at the U.S. Army Edgewood Chemical Biological Center (ECBC), Aberdeen Proving Ground, MD.

“A signature is a characteristic infrared pattern exhibited by all chemicals when they interact with infrared light (also known as photons)—the light is absorbed or emitted by chemical bonds in the compound,” explained Samuels. Since each chemical agent is made up of a particular arrangement of chemical bonds, the infrared signature is specific to its molecular structure.

“Our current efforts are focused on how to better record this signature either through enhanced digital or optical signal processing or by better understanding the background photon environment in which the remote sensor operates so that we can correct for background effects that interfere with the agent signatures,” said Samuels.

“A signature is a characteristic infrared pattern exhibited by all chemicals when they interact with infrared light (also known as photons)—the light is absorbed or emitted by chemical bonds in the compound,” explained Samuels. Since each chemical agent is made up of a particular arrangement of chemical bonds, the infrared signature is specific to its molecular structure.

“Our current efforts are focused on how to better record this signature either through enhanced digital or optical signal processing or by better understanding the background photon environment in which the remote sensor operates so that we can correct for background effects that interfere with the agent signatures,” said Samuels.

The passive standoff detection team is also working on building better signature libraries that consider variables like purity or impurity of the chemical agents, or the presence of any ancillary chemical components that accompany the agents when they are disseminated in a chemical attack.

Just as a dirty bomb isn’t composed of purely radioactive material but also combines conventional explosives, such as dynamite, a released chemical agent won’t necessarily be pure but may contain several other chemical compounds in addition to the main compound, such as sarin.

Samuels was part of team of researchers who did a chemical and biological sensor standards study for the Defense Advanced Research Projects Agency (DARPA), another DoD agency interested in improved chem/bio detection. In the study, four key parameters were identified as the most accurate ones to use to characterize the performance of a chem/bio agent sensor. The parameters are sensitivity, probability of correct detection, false positive rate and response time, which can be combined to indicate the sensor’s receiver operating characteristic (ROC). The report states that the preference is to have sensors capable of switching from one operating mode to another based on the mission.

The ROC curve typically plots the sensitivity of the sensor as a function of false alarm rate for a given detection confidence and response time.

“The probability of detection and response time refer to how reliably the sensor responds when a real agent is present and how quickly it completes its analysis and reports an alert,” said Samuels. “These two parameters are important because soldiers need to be given enough warning when a chemical agent appears in their area of operations that they can put their protective gear on.”

“In order to compute a ROC curve, many measurements must be performed to establish the concentration levels to which the sensor is sensitive, and many more measurements must be performed in realistic environments to develop a statistical feel for how often the sensor will report a false positive detection,” said Samuels.

The most important feature that DoD has discovered about detector reliability is its specificity. The more specific a sensor is, the lower its false alarm rate. A false alarm results when the sensor cannot distinguish between a commonly occurring environmental pollutant (such as an insecticide) and a chemical warfare agent. It’s simply human nature that if there are too many false alarms, the soldier will start paying less attention to the detector.

Thomas, from General Dynamics, agrees. “The number one problem and the biggest concern when developing detectors is reliability—if a system generates a high false alarm rate it will tend to be dismissed by the operator.”

There are roughly a dozen traditional warfare agents. But, the fact is that there are at least 100 TICs/TIMs, according to Thomas. “A bug spray used at a higher level can be considered dangerous,” he said.

General Dynamic’s JUNO system features a high degree of specificity, which reduces or eliminates false positive detection. JUNO’s basic design utilizes a proprietary sensor engine that provides a differential-mobility-spectroscopy-tunable ion mobility filter. The filter utilizes an oscillating electric field with a superimposed DC “tuning” field. During operations, ions in a range of mobility can be identified as the tuning field is scanned.

DARPA is also funding a very sophisticated detector known as a micro-gas analyzer (MGA). According to DARPA, the MGA program seeks to attain tiny separation analyzer-based chemical warfare agent sensors capable of orders of magnitude reductions in analysis time, detection limit, and power consumption while maintaining true and false alarm rates on par with bench top gas chromatograph/mass spectrometer systems.

Meanwhile, the passive detection team at the ECBC continue their painstaking research. They are conducting research on “environmental backgrounds in order to better understand the constituents that give rise to false positives, and are studying sensor platforms that can better compensate for interfering signals and identify the chemical agent signatures with higher specificity,” explained Samuels One method the team uses to accomplish their research goals is chemical imaging. “In the chemical imaging platform, the scene is broken up into many pixels the same way a digital camera captures an image, only each pixel is resolved spectrally by the chemical sensor,” said Samuels. “The M21 has only one pixel, and so can only report that it has detected a threat signature in its field of view. The imager can use the neighboring pixels to those in which a chemical signature is detected to better correct for background variations and improve sensitivity and reliability. Coupled with an improved signature library, these improvements should lead to a lower false alarm rate and higher detection confidence,” said Samuels.

General Dynamics’ JSLSCAD is the first chemical detection system to furnish 360-degree coverage for ground- and sea-based platforms and an aerial craft detection range of 60-degrees at as far as 15 miles, allowing personnel to avoid contaminated areas or the need to don protective masks and clothing. A version of the device is also being designed to go on military helicopters.

This unit uses a passive infrared detection system that analyzes light emitted by the surrounding atmosphere in the 7 to 14 micron wavelength range to detect chemical agent vapor clouds.

On the point detector side, one way to improve the sensor performance would be to incorporate more than one detection phenomenon into the platform, making it an “orthogonal” detection platform, according to ECBC researchers. “The most common fielded chemical sensors rely on ion mobility spectrometry to identify chemical warfare agents,” said Samuels. “If an additional detection mode is employed, one which is based on an alternative chemical property such as a flame photometric signature that confirms the presence of telltale elements such as phosphorous and sulfur, then the two sensors working together will provide an enhanced ability to reject false alarms.” Samuels explained that research is also being done at ECBC on the use of chemically-functionalized nanosensors as well, which measure an electrical signal when certain specific chemical reactions occur in the sensor only when a chemical agent is present.

While it sounds as though sensor detection technology is moving forward at a geometric pace, Samuels and his colleagues have a number of ideas/areas for future research.

“I am interested in the development of a single sensor platform that can warn of the presence of both chemical and biological agents with high confidence and low false alarm rates,” said Samuels. He continued, “Some of my research is directed toward the development and interpretation of the optical signatures of biological warfare agents. I am endeavoring to develop sensor concepts and architecture that will allow the system to simultaneously analyze solid particles, liquid aerosols and chemical vapors, and chemo-metric analysis of the signatures to afford high detection confidence and specificity.”

And Samuels has by no means exhausted research possibilities in the sensor detection arena. “I am also enthusiastic about the advent of nanosensor platforms that are being studied by other scientists at ECBC. These platforms could evolve into throwaway sensors that are very inexpensive.”

Environics

Environics USA, a wholly owned subsidiary of the Finnish-based Environics OY, has developed the ChemPro100 handheld detection and identification system. The system is based on their open loop ion mobility spectrometry (IMS) technology and uses the improved Ion Mobility Cell to provide improved selectivity and sensitivity. It is designed to detect chemical warfare agents and toxic industrial compounds/materials.

The ChemPro100 weighs less than two pounds and is powered by a rechargeable battery pack or six AA batteries. The system has an easy to use operator interface, which can be operated single handed. The user display provides the operator with battery life indicator, concentration bar display, agent class, agent ID, horn volume level, date and time. The system stores agent alarm information for retrieval at a later time to provide a historical log of events.

The ChemPro is small enough to be used as a personal detector, a monitor for surveying after an event or a fixed installation detector. It provides continuous operation without the need of expendable desiccant cartridges, like other IMS systems. The ChemPro100 has no expendables and is designed for low life-cycle and operating costs.

Environics also makes the M90-D1-C chemical warfare agent detector designed to detect and identify nerve, blister, and blood and choking agents.

Protecting the Future

The idea of a chemical or biological attack will always be a somewhat frightening thought. Advance detection is a key element in countering those sorts of attacks. Thanks to the efforts of organizations such as the Edgewood Chemical Biological Center and innovative industry partners, sensor science continually improves so miosis will never be the first warning.



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