Handbook of Infra-red Detection Technologies
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One coating provides various responses to several different chemical warfare agents, and the differences are usually large enough for the device to differentiate among agents. Current technology can detect and identify a wide range of chemical warfare agents with only six different coatings.
However, more coatings may be needed for higher degrees of specificity for large target populations like TICs. If the new agents respond to existing coatings, it will be fairly simple to change the detection software to recognize them. If not, new coatings must be developed.
SAW sensors are used in mobile detectors to detect nerve and blister agents. With further development, SAW technology could also potentially detect a large number of chemical compounds and biological agents. An electrochemical sensor detects and measures changes caused by the interaction between the chemical agent and the properties of an electrical circuit Taylor and Schultz, Fundamentally, electrochemistry is based on a chemical reaction that occurs when the chemical agent enters the detection region and produces some change in the electrical potential.
This change is normally monitored through an electrode. A threshold concentration of agent is required, which corresponds to a change in the monitored electrical potential. Electrochemical sensor technology can be used in a wide variety of configurations. Currently, it is used in mobile detectors to detect blister, nerve, blood, and choking agents. Photo-ionization detectors PIDs operate by passing an air sample between two charged metal electrodes in a vacuum region irradiated with ultraviolet radiation, thus producing ions and electrons. The negatively charged electrode collects the positive ions, thus generating a current that is measured by an electrometertype electronic circuit.
The measured current can then be related to the concentration of the molecular species present. PIDs are used in mobile detectors to detect nerve, blister, and mustard agents. In flame photometry, an air sample is burned in a hydrogen-rich flame.
The compounds present emit light of specific wavelengths in the flame. An optical filter is used to let a specific wavelength of light pass through, and a photosensitive detector produces a representative response signal. Because most elements emit a unique, characteristic wavelength of light when burned in this flame, the flame photometer can detect specific elements. Flame photometers are commonly used with gas chromatographs. Sulfur and phosphorous flame photometry are often used to detect mustard and nerve gas, respectively. Like infrared spectroscopy, photoacoustic infrared spectroscopy PIRS uses the selective absorption of infrared radiation by chemical agent gases to identify and quantify the agent present.
Pulses of a specific wavelength of infrared light are sent into a sample through an optical filter, and the light transmitted by the filter is selectively absorbed by the gas being monitored, which increases the temperature and pressure of the gas. Because the light entering the cell is pulsating, the pressure in the cell fluctuates, creating an acoustic wave directly proportional to the concentration of the gas in the cell. Microphones mounted inside the cell monitor the acoustic signal and send results to the control station. PIRS technology is fairly well established, but its use for chemical warfare agent detection is fairly new.
It is anticipated that a large number of agents can be detected with this technology.
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The molecules of many compounds absorb waves in the infrared region of the electromagnetic spectrum, and the wavelength at which absorption occurs is unique to specific compounds, which provides identifiers for different compounds. Rotational and vibrational interactions occur with electromagnetic radiations that have longer submillimeter to millimeter wavelengths. These regions include the far-infrared and radio frequency microwave spectrum. Research on the absorption of these wavelengths for detecting chemical agents is under way U.
If the absorption of energy at these wavelengths is sufficient, microwave spectroscopy-based technologies similar to infrared spectroscopy methods may be another way of detecting chemical agents. Only a few on-line techniques have been developed for detecting and characterizing small aerosol particles.
Conventional methods involve isolating particles on filters and subsequent analysis performed in the laboratory. The isolation processes often disturb the aerosol and thus render the data questionable because the particles often evaporate or react before analysis. Newer spectrometers using gentler vaporization strategies will probably overcome this problem. This technique provides the size and chemical composition of individual aerosol particles in real time. Some examples of aerosol systems that are being characterized in the laboratory using ATOFMS include secondhand tobacco smoke, suspended soil dust, sea salt aerosols, and a variety of combustion particles.
In recent field studies, transportable ATOFMS instruments were strategically positioned at sites where the evolution of single particles in the atmosphere could be monitored over time. In regional and international studies, these transportable instruments are being used to study the direct effects of aerosols on visibility, pollution levels, and global radiation. Some newer instruments use hot surfaces rather than lasers for aerosol vaporization. If these "hot-surface" systems can preserve molecular structure, they may be crucial to the future identification of specific chemical agents and TICs bound to aerosols.
Enzymes can be used with immunoassays to detect the presence of, and quantify the concentration of, many chemical substances Ngo and Lenhoff, The essential components of an enzyme immunoassay are an antibody that binds to a specific target substance chemical agent and an enzyme that makes detection of the bound antibody possible. Immuno-assays performed in a solution, for example, respond to the initial reaction of the antibody and its chemical, which then modulates the catalytic activity of the enzyme, allowing detection. The sensitivity of an enzyme immunoassay depends on how well antibodies home in on a particular antigenic target, such as a chemical agent or a protein, a bacterial or viral antigen, or other antibodies.
A detection system that combines this specificity with the catalytic ability of some enzymes to convert colorless chemicals to brightly colored products could be adapted to a wide range of applications. Immunoassays are increasingly being used to detect environmental contaminants. Enzyme immunoassays can be very sensitive down to the parts per trillion [ppt] level and very specific. However, they are much too slow for rapid chemical detection. Another problem is that some substances do not readily create antibodies.
Currently available equipment for detecting and monitoring chemical agents range from simple systems, such as detection paper, to complex mobile sampling vehicles, such as the FOX vehicle. The following subsections contain a review of the capabilities and limitations of these systems, most of which have been developed singly or jointly by branches of the military a few have been commercially developed but are available for military use.
Army, , ; U. Army and U. Marine Corps, ; briefings to the principal investigator and advisory panel by the U. Navy, The M8 and M9 detection papers provide rapid less than one minute , inexpensive tests for the presence of liquid mustard or nerve agents. The paper is used only for screening, and results must be verified by more accurate detection methods, particularly because of the paper's propensity to show false positive results for some substances, such as petroleum products and antifreeze. M8 paper is used by ground troops to detect liquid chemical agents.
It is capable of detecting Levinstein mustard H and Lewisite blister agents and fluorine-or cyanide-containing organophosphates G and sulphur-containing organophosphorous compounds V nerve agents. It is not used as the sole basis for agent identification, however. M9 paper, which is similar to M8 paper, comes in a long dispenser roll. M9 paper is an adhesive-backed, tapelike material designed to be worn on the outside of clothing or placed on vehicles, equipment, or supplies that may be exposed to chemical agent droplets.
Current detection kits are the M kits and the M18 kit. The MA1 contains disposable plastic sampler detectors, a booklet of M8 paper, and a set of instruction cards. The sampler detectors are enzyme-based detector "tickets" that change color to indicate low concentrations of cyanide, vesicant, and nerve agents in vapor form. The tests take approximately 15 minutes and may provide a negative reading at concentrations that are below the immediately-dangerous-to-life-and-health IDLH level but are still hundreds of times higher than the AEL.
The MA2 kit contains a colorimetric device for measuring the concentration of selected airborne chemicals and has approximately the same sensitivity.
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Tests for each take two to three minutes but must be conducted in series, not simultaneously. Local detection systems produce an alarm or warning and work at close range point detection. Most of these are "alarm-only" systems that do not provide any information about agent concentrations except that they are above the sensitivity level of the detector.
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Many do not even identify the agent that set off the alarm. The M8A1 is an automatic chemical agent detection and warning system designed for the point detection of nerve agent vapors or inhalable aerosols by ionization methods in a baffled-flow electrode configuration that filters out the lighter background ions from the heavier agent ions.
The M22 is an "off-the-shelf," automatic, chemical agent alarm system based on IMS technology that is capable of detecting and identifying standard blister and nerve agents. The M22 system is man-portable, can operate automatically after system start-up, and provides an audio and visual alarm. An important feature of the M22 is that it can be linked to other systems, such as the multipurpose integrated chemical agent detector MICAD , to support battlefield automation systems.
The M90 automatic agent detector AMAD is a portable unit used to indicate the presence of nerve, blister, and blood agents. The M90, which uses IMS techniques, is an alarm-only device that can monitor up to 30 chemicals in parallel. The M90 is a fast-acting, relatively sensitive device that provides an alarm in about 10 seconds for nerve agents and mustard and about 80 seconds for lewisite.
The ICAD is an 8-ounce pocket-mounted device that simultaneously detects nerve, choking, blood, and blister agents based on electrochemical techniques. It is easy to operate, requires only minutes of training time, and has both visual and audible alarms. Sensitivities are in the range of 0.
ICAD was developed for the U. The CAPDS is a fixed system capable of detecting nerve agents in vapor form using a baffled-flow electrode configuration ionization technique. It generates an alarm signal that is sent to the Damage Control Central and the bridge. This system is installed on most surface combatant ships.
Stand-off systems produce an alarm or warning from a distance, warning of an agent before troops move into the area. The M21 alarm detects nerve and blister agent clouds at line-of-sight distances out to 5 km. Point local monitoring devices are designed to collect samples and monitor chemical concentrations in the environment in which troops are currently located. These portable, handheld, point-detection instruments monitor nerve or vesicant agent vapors.
They provide graduated readouts eight bars. They detect vapors of chemical agents by sensing molecular ions of specific mobilities time of flight and use timing and microprocessor techniques to reject interference. The monitors, which consist of a drift tube, signal processor, molecular sieve, membrane, and expendables e. The monitors are 4-inches by 7-inches by inches and weigh approximately 5 pounds. The ICAM has minimal maintenance requirements. Response time depends on concentration but generally takes from 10 to 60 seconds.
One obvious drawback, therefore, is an inability to check the efficacy of decontamination, both in the field and subsequently at treatment facilities. The SAW Mini-CAD is a commercially available, pocket-sized instrument that can automatically monitor for trace levels of toxic vapors of both sulfur mustard and the G nerve agents with a high degree of specificity. The instrument is equipped with a vapor-sampling pump and a thermal concentrator to provide enriched vapor sample concentration to a pair of high-sensitivity coated SAW microsensors.
All subsystems are designed to consume minimal amounts of power from onboard batteries. Optimal use of the SAW Mini-CAD requires a compromise among the conflicting demands of response time, sensitivity, and power consumption. Maximum protection requires high sensitivity and a rapid response. The state-of-the-art systems for detecting any chemical agent are laboratory-quality gas-chromatography systems, most of which are heavy up to pounds.
They also require a or V AC power supply and, thus, have limited portability. Although gas chromatography systems take up to 10 minutes for an analysis, they are highly sensitive and very specific, and they can detect most chemical warfare and many toxic chemical agents below the AEL levels. Gas chromatography systems, which are versatile and can detect thousands of chemicals, come with extensive chemical spectra libraries. The mini-CAM is a continuous air-monitoring system that uses gas chromatography and selected detectors and samplers to monitor for the presence of chemical agents.
It weighs 10 pounds and is easily portable. Mini-CAMs were developed for monitoring air at storage and demilitarization facilities. They can detect most nerve, blood, blister, and choking agents at the Surgeon General's 8-hour time-weighted AEL. They have about a five-minute detection time and can operate 24 hours a day for up to seven days. Write a product review.
Handbook of Infrared Detection Technologies
Back to top. Get to Know Us. English Choose a language for shopping. Audible Download Audio Books. DPReview Digital Photography. Shopbop Designer Fashion Brands. We also welcome non-commercial technical documents subject to editorial review and post them free. Infra-red IR gas detection is based on the absorption of energy by hydrocarbons. The bond between hydrogen and carbon absorbs proton energy at a wavelength of 3.
The wavelength is carefully selected to accurately measure the concentration of methane and other hydrocarbon gases in air, ensuring that the measurement is not effected by water vapour or other gases. There are also point type IR gas detectors. A beam of IR energy is emitted between a source and detector and any attenuation caused by hydrocarbons in the beam being electronically processed to give a reading in LEL metres.
In order to ensure that dirty lenses, mirrors or other related issues do not cause errors two detectors are generally utilised and their measurements compared. In order to reduce or eliminate the effects of other interfering light sources, particularly direct and reflected sun light, but also flames and welding arcs, higher-specification instruments employ strong pulsed light sources, and the times at which measurements are taken are synchronised with the timing of the light pulses. Transmitter and Receiver units may incorporate heated optics designed to minimise the build-up of humidity, condensation, snow or ice on the glass windows, which could obscure the optics in extreme conditions.
The sophisticated open-path technology provides immunity to sunlight and minimises the effects of environmental factors such as rain, fog, ice, snow and condensation. The sample detector input is filtered at wavelengths where strong infrared absorption is exhibited by the target gas. The reference detector input is filtered at nearby wavelengths, where strong infrared absorption is not exhibited by the target gas.
Handbook of Infra-red Technologies
By calculating the ratio of the sample to reference signal it is possible to measure the quantity of gas in the beam, whilst compensating for the effects of rain, fog, dirt etc. Calibration for a gas concentration is expressed in LEL - metres. For various gases low and high test filters are used for calibration eg.
For more complex situations, gas tubes that can be inserted in the beam path and filled with specific gas mixtures may be employed to calibrate Open Path Gas Detectors. OPGD beam paths need very careful design to ensure an uninterrupted Line of sight, this should occur at the detailed design stage. It is recommended that if a 3D model is available this tool is used to verify this.
A beam of IR energy is emitted between a source and detector and any attenuation caused by hydrocarbons in the short beam being electronically processed to give a reading in LEL Lower Explosive Limit. Commonly a reference beam is utilised to overcome any reduction in beam intensity due to fouling of the optics, fog, temperature effects etc. The following Infra-Red Gas Detector references are from sources which provide what ICEweb considers to be the best technical and educational information on the subject. Should there be any issue with ICEweb providing this information, please contact us and we will remove it immediately.