CBRNE - Chemical Detection Equipment 

Chemical detection equipment (CDE) is an essential component of hazardous material (HAZMAT) emergency response. This equipment should detect the harmful agent, correctly identify the agent, and define the area of exposure. Rapid detection is essential so that responders and military targets can recognize a threat and don protective gear (ideally in < 9 s). It is also important to know the extent of contamination. During several documented chemical attacks, first responder casualties have been vast enough to delay the rescue. During the Tokyo subway sarin attack in 1995, 9% of emergency medical services (EMS) providers suffered the affects of acute exposure. Effective CDE may help prevent these occurrences.

Several different technologies are used today to detect chemical agents (CAs). CAs are defined as chemicals intended to kill or seriously injure human beings. CDE usually detects the most common CAs: nerve agents, blister agents, and arsenical vesicants. A large variety of equipment is available that is capable of identifying liquid droplets of CAs on surfaces and in vapors. Laboratory-based equipment can detect agents in water, food, and human samples. The main challenges with these technologies are ensuring an appropriate sample for analysis and filtering out nonhazardous environmental chemicals that may be present. A device may detect agents quickly and accurately in a rural setting only to be confused in an urban city by the exhaust from a vehicle.

This article focuses on the technologies and devices that may be used by first responder teams in the field. Laboratory detection techniques are beyond the scope of this discussion.

Chemical detection paper is a very sensitive technique for detecting CAs. It is one of the least sophisticated and thus least expensive methods of detection. It is used to detect liquids and aerosols and is a common means for defining a contaminated area.

Chemical detection paper is composed of 2 dyes soluble in CAs and a pH indicator integrated into cellulose fibers. When exposed to CAs, it can change color according to the type of agent. If an aerosolized droplet encounters the paper, the diameter and density of the spot can be used to determine the droplet size of the agent and the degree of contamination.

Chemical detection paper lacks specificity and is prone to error because it reacts with contaminants such as brake fluid, antifreeze, and insect repellent, resulting in false-positive readings. False readings are especially undesirable in civilian situations because they may lead to mass panic. Therefore, always use chemical detection paper with another modality for accuracy of detection.

M8/M9 chemical detection paper

M8 and M9 chemical agent detection papers, commonly used by the military, are available commercially to HAZMAT response teams. M8 paper is packaged in 25 perforated sheets, 2.5 in X 4 in, and is blotted on liquids that arouse suspicion. It identifies CAs by changing colors within 30 seconds of exposure: dark green for persistent nerve agents, yellow for nonpersistent nerve agents, and red for blister agents.

M9 paper has adhesive backing that allows it to be attached to clothing and equipment. M9 paper detects the same agents as M8 paper but does not change color to enable identification. M9 paper tends to react faster than M8 paper and can be attached to vehicles that are entering areas filled with vapor to determine contamination. Vehicles thus equipped are limited to a speed of 30 km/h.

M256A1 chemical agent detection kit

The M256 chemical agent detector kit was originally released in 1978 and was modified in 1987 to the M256A1, which is sensitive to lower concentrations of nerve agents. It was used extensively during the Gulf War but is also available commercially. It is another common component of chemical detection equipment (CDE) provided to civilian response teams. This portable kit detects nerve gas, mustard gas, and cyanide and usually is used to define areas of contamination.

The M256A1 contains a package of M8 paper, detailed instructions, and a vapor sampler (12 enzymatic tickets that contain laboratory filter paper for detecting CA vapors). The vapor sampler uses wet chemistry technology, in which ampules containing different substrates are crushed so that the liquids interact with strips of filter paper, chromatographic media, and glass fiber filter. These substrates then are exposed to the vapor under suspicion. The reaction causes a color change, alerting the user to the presence of a CA. The reactions typically take 15 minutes to occur.

The M256A1 can detect nerve gas concentrations of 0.005 mg/m³, hydrogen cyanide concentrations of 11 mg/m³, and mustard gas concentrations of 0.02 mg/m³. This is one of the military's most sensitive devices for detecting CAs and detects all agents at levels below those that can kill or injure people. It is prone to false-positive results, similar to other enzymatic detection techniques, but it has not been demonstrated to produce false-negative results in real situations.

Colorimetric tubes

Colorimetric tubes such as those available from Draeger and RAE systems use enzymatic techniques to identify CAs. A hand pump is used to draw a sample into a specific tube, and the concentration of the substance is read from the tube. This is another simple and inexpensive way of detecting and identifying a CA. It is used extensively in civilian response units for this reason, but it has some disadvantages. Available are 160 substance-specific reagent tubes identifying different agents. For each agent, a different tube must be used. Efficient use of this system demands knowledge of which CA is likely to be present in a given environment. If a tube for vesicants is used to sample the air and the CA is a nerve agent, the tube reports a false-negative result. A tube for each possible CA must be used for thorough detection.

Draegar has made this process simpler by offering a chip measurement system analyzer (CMS). The analyzer integrates an optical system for analyzing the color reaction, a flow controller, a pump system, and 10 capillaries, each capable of detecting an agent. As long as the proper chip is inserted, 10 agents can be detected and measured accurately within 20 seconds using this device. Draegar offers this device as part of an emergency response kit available to the public.

Ion mobility spectroscopy (IMS) is used in many handheld and stand-alone detection devices that can be used to scan equipment, surfaces, and people for contamination. This technology involves drawing a gaseous sample into a reaction chamber using an air pump. The air molecules then are ionized, most commonly using radioactive beta emitters such as nickel-63 or americium-241. The ionized particles then are passed through a weak electrical field toward an ion detector.

Contaminants are identified according to the time it takes to traverse the distance to the detector and the amount of electrical charge detected. The time is proportional to the mass of the molecule. The pattern is compared to a sample of clean air; if the pattern is markedly different and unique to certain types of agents, the alarm sounds. These systems are capable of detecting and distinguishing between nerve gas, mustard gas, and vesicants. Its sensitivity ranges from 0.03 mg/m³ for nerve gases such as sarin to 0.1mg/m³ for mustard gas.

IMS has certain advantages. It is less sensitive to contaminants, because it relies on a clean air sample for calibration. Thus, if an area has a certain baseline nonhazardous environmental vapor present, it is not detected. Differential ion mobility spectrometry (DMS) is a variation of IMS that measures the difference between the ion mobilities as they pass through the field to separate ions.

Improved Chemical Agent Monitor and other handheld devices

IMS is the cornerstone of many devices used today. The Finnish M86 and M90 are handheld devices that use IMS, as is the Improved Chemical Agent Monitor (ICAM). The ICAM was used extensively in the Gulf War, even attached to certain vehicles. It is a handheld device that continuously displays the concentration of nerve agents or mustard agents. The ICAM is prone to erroneous detection in enclosed spaces and areas of strong vapor concentration (eg, heavy smoke). It also can become saturated, requiring recalibration. Versions of the ICAM are available for commercial purchase and are used by many medical response teams.

The Advanced Portable Detector (APD) 2000, manufactured by Smiths Detection, is another common device that uses IMS and is sold commercially to HAZMAT response teams for domestic preparedness. This handheld device can be powered by batteries and can detect mace and pepper spray as well as nerve agents, blister agents, and hazardous compounds.

The Sabre FR also uses IMS and is manufactured by Smiths Detection. It is in use by first responders because it can use vapor or trace particle samples to detect explosives, drugs such as cocaine and heroin, as well as chemical agents.

Stand-alone detectors - M8A1, Automatic Chemical Agent Alarm, and Fixed Site/Remote Chemical Agent Detector

Many stand-alone detectors also use IMS technology. The military uses the M8A1 detector that consists of a stand-alone detector, which continuously monitors the environment for hazardous vapors and aerosols, and up to 5 alarms that can be dispersed throughout an area. The M8A1 detects nerve agents and blister agents when the concentration is 0.1 mg/m³ or greater and alarms within 1-2 minutes. M8A1 is an ideal device for protection from off-target attacks, in which a vapor is released upwind from the targets. However, it is less effective for on-target attacks, in which the CA is released in large amounts within seconds. In this situation, the alarm sounds after the personnel have been exposed. This system was used during the Gulf War and has been upgraded to the Automatic Chemical Agent Alarm (ACAA) system. The ACAA is slightly larger and has a communications interface that is useful in combat.

Smiths Detection provides a commercial version of an IMS stand-alone detector called the Centurion II. This system detects and identifies nerve and blister agents and offers superior reliability from interference. The alarm information can be transmitted via radio, satellite, or hardwiring. This system can be useful if placed in hospital wards or at victim collection sites to detect contamination.

Infrared radiation (IR) is used in several CA detectors, including long-range detectors and point detectors. Mid-IR light (frequency 4000 cm^-1 to 200 cm^-1) can be used to excite molecules, and each agent has a unique infrared pattern referred to as a fingerprint. Several different detection techniques use IR, including photoacoustic infrared spectroscopy, filter-based infrared spectroscopy, forward-looking infrared spectroscopy (FLIR), and Fourier transform spectroscopy.

Photoacoustic infrared spectroscopy

This highly selective technique is used to identify CA vapors. It usually is used in point detector devices. Modulated IR is passed through the sample. Since the CA absorbs the radiation, the temperature increases, and per Boyle law, the gas expands. The pattern of expansion or contraction depends on the modulation of the IR, which in photoacoustic spectroscopy is an audible signal. A microphone detects the modulation and alarms when it is similar to a recognizable agent.

This technique's selectivity is based on the number of wavelengths transmitted through the sample. As more wavelengths are passed, the chance of contaminants causing false alarms decreases. These devices are sensitive to environmental variables such as external vibration. Like IMS, if these devices are calibrated in the operating environment, detection should be accurate.

Filter-based infrared spectroscopy

This technology also is based on comparing the amount of energy absorbed by the sample, using several different wavelengths of infrared light. A series of filters is used to direct the beam through a predetermined path. Concentrations of each vapor component are used to compile trends and identify the vapor.

Differential absorption light detection and ranging

This infrared technology is used mainly to track CA clouds that already have been identified. Two pulses of laser are transmitted into the distance, and the reflected IR is detected. One pulse is a frequency that is known to be absorbed by the CA; the other is not known to be absorbed. The difference in the intensity of the return signal is used to determine the concentration of the cloud, while the time of return is used to determine the distance from the observers. This technique also is subject to environmental noise but has been used effectively to track CAs.

Passive infrared detection

FLIR and Fourier transform infrared (FTIR) are techniques by which IR emitted from CA vapor is detected simply. These technologies commonly are used in stand-alone detection devices that simply alarm when a CA cloud is detected. Both of these methodologies depend on the collection of infrared information; however, the processing is different.

M21 Remote Sensing Chemical Agent Alarm

The military uses the M21 Remote Sensing Chemical Agent Alarm (RSCAAL) based on passive infrared detection. It is the first fielded standoff chemical detection device. This system can detect a vapor cloud from 5 km with an 87% detection rate. The M21 RSCAAL continuously monitors a background and notes the change in spectral information if a vapor cloud obstructs the background. It automatically scans along a 60° angle, allowing the operator to monitor horizontal movement. The M21 can be set up in 10 minutes and is unaffected by low light conditions. However, the M21 is limited in that it must be stationary and can be obstructed by snow and rain.

Photo ionization detection

Gas vapors can be ionized using ultraviolet light. Photo ionization detection depends on exposing the suspect vapor to ultraviolet energy powerful enough to ionize agent molecules. Specific ranges of ultraviolet light ionize molecules in certain CAs. An ion detector then registers the amount of ionized molecules. Thus, these detectors can determine the concentration and identity of the agent. Handheld detectors produced by RAE systems and Photovac are examples of detectors that use this technology.

Flame photometry

Another technology used is flame photometry. In this technique, a flame of hydrogen is used to burn a sample of air. The color of the flame is analyzed by a photometer for concentrations of sulfur and phosphorous (key components in nerve gas and mustard). Flame photometry is highly sensitive yet is prone to false-positive results by detecting other gases that contain significant concentrations of sulfur or phosphorus but are nonhazardous.

Certain analysis algorithms can be used to make these detectors less prone to error. If gas chromatography is integrated with flame photometry, the detectors are more accurate. Gas chromatography is a technique used in laboratories to separate mixtures of compounds. It involves using a carrier gas to separate a volatilized liquid or vapor based on its passage through a column. As each solute exits the column according to its properties and the temperature of the column, a detector records an electrical signal plotted over time.

The AP2C handheld detector manufactured by Arrow Tech Inc uses this technology. Per the manufacturer, it can detect sarin at a concentration of 10 mcg/m³ in 2 seconds. Federal agencies and international agencies use this for mass screenings and for confirming decontamination of casualties.

Miniature automatic continuous agent monitoring system

The miniature automatic continuous agent monitoring system (MINICAMS) is a system based on combining gas chromatography with flame photometry. A sample vapor is drawn into the machine and exposed to a heated preconcentrator loop. As each component exudes from the column, it is exposed to flame photometry. This system enables more specific detection. A typical cycle lasts 3-5 minutes, enabling continuous monitoring of the environment.

Surface acoustic wave detection

Surface acoustic wave (SAW) chemical detectors rely on chemically selective coated piezoelectric crystals that absorb target gases. The absorption causes a change in the resonant frequency of the crystal that is measured by a microcomputer. These detectors are able to identify and measure many CAs simultaneously. These devices are produced inexpensively, making them a popular choice among civilian response units. The SAW MiniCAD mk II manufactured by Microsensor Systems Inc is a portable SAW array detector that is lightweight, battery operated, and available commercially. It is used remotely to define areas of decontamination but also can be used for active detection.

The Joint Chemical Agent Detector (JCAD) ChemSentry also uses SAW technology and is produced by BAE. It weighs approximately 2 pounds, is designed to be used by every department of the military, and is available commercially. It can be used as a personal protection detector to be carried by troops as well as to monitor ships, cargo holds, and wheeled vehicles. It uses a preconcentrator to detect low levels of a specific chemical agent requiring 20 minutes for sample collection but simultaneously monitors ambient air for larger concentrations of most chemical warfare agents.

Electrochemistry

A very selective, yet not as sensitive, detection technology uses electrochemicals. These detectors monitor a change in a chemical reaction or a change in a thin film that reacts to chemicals in the air. For example, one such detector has a monitors a solution with a known source of cholinesterase, which interacts with nerve agents. If air containing the agent mixes with the cholinesterase, the concentration of the enzyme will decrease indicating the presence and concentration of an agent. These detectors are very susceptible to changes in the environment as temperature changes can affect the reaction.

Carbon nanotube gas ionization sensors

An emerging technology that may soon be used for chemical agent detection is based on miniaturized carbon nanotube sensors. The tips of nanotubes generate high electric fields that when exposed to different gases will exhibit different electrical conductances. This difference in conductances can be used to identify gases and mixtures of gases in a similar fashion to the IMS method of detection.

Previous generations of nanotube sensors have been limited by sensitivity to changes in environmental conditions, the inability to identify gases with low energies, and poor charge transfer. One group at RPI has developed a gas ionization sensor that generates high electric fields at low voltages.^[1] Their sensors have good sensitivity and can be compact and battery powered. They have been shown to detect 1% mixtures of ammonia and argon at room temperature in less than 20 microseconds. This technology offers many advantages over flame photometry, photoionization, and other techniques.

The Cyranose 320 manufactured by Smiths Detection integrates these sensors into an array to make a compact, portable, and reliable device that is used for quality control and to detect volatile organic chemicals within one minute. It can be customized to individual use but cannot be deployed as a chemical agent detector at this time.

The Department of Homeland Security (DHS) in conjunction with several government agencies including the Interagency Board for Equipment Standardization and Interoperability (IAB) has a goal to subject existing chemical detection equipment to laboratory testing and evaluation against a specified protocol and to develop a series of documents, including national standards, user guides, and technical reports. While this multi-year process takes place, they maintain a guide that is derived from market surveys of commercially available detection equipment.

Most recently, in January 2007, this guide identified 207 detection devices available to the military and first responders. With many different detectors and technologies available, DHS recommends examining 16 factors when choosing a detection device. The table below lists these factors. The most sensitive detectors tend to be most susceptible to false-positive alarms. Thus, for most practical applications, multiple detectors are needed to verify the findings of the initial detector.

Table 1. Factors to be Examined When Choosing a Detection Device (Open Table in a new window)

Anyone who is considering purchasing chemical detection equipment (CDE) should obtain this guide, which is available online and is listed in the References.

CDE technology has advanced primarily as a result of military necessity. More recently, the need for civilian preparedness for terrorist attacks with chemical agent (CA) has been recognized. Civilian response is different from military response in many ways, and the choice of CDE must take this into account.

Key differences include the following:

• Civilian responders tend to be less experienced in chemical attacks.
• Civilian responders have less information concerning the origin and type of attack and may not recognize that it is a CA attack initially.
• Civilian responders have more stringent budget restraints and thus must use cost-effective equipment.
• Civilian responders have less latitude in incorrectly identifying a CA.
• Civilian responders are deployed primarily to provide medical care, leaving detection as a secondary goal.

In the civilian setting, EMS or other medical providers are the first to arrive (see EMS and Terrorism). Most EMS providers do not carry CDE to detect CAs and thus initially must recognize the potential threat in order to notify specialized HAZMAT response teams. These teams exist in many cities and are at a minimum equipped with pH paper and combustible gas indicators. This equipment is inadequate in identifying most CAs. Other teams now are equipped with colorimetric tubes (see Enzymatic Detection Techniques). Colorimetric tubes are much less expensive than more technical devices, such as the ICAM, and can be distributed generally.

Major cities in the United States have a Metropolitan Medical Strike Response System (MMRS) organized by the Public Health Service. These are highly specialized, fully equipped, deployable teams to combat civilian threats from weapons of mass destruction. They are primarily medical providers who provide EMS services, decontamination, detection, and treatment. The first such team was organized in 1995 in Washington, DC, and a second was organized for the 1996 Olympics in Atlanta. They are now present in 124 jurisdictions and receive over $300,000 annually through the Department of Homeland Security.

MMRS teams are often better equipped to respond to CA attacks than HAZMAT response teams. Even so, wide variability exists in the type of detection devices used. A recent study by the National Guard recognized that no standards regulate the detection devices among different civilian emergency response units. MMRS teams can employ any of the devices and technologies described above. They commonly use inexpensive CDE such as SAW detectors and enzymatic techniques such as M9 paper and the M256 kit. Some teams also use IMS devices such as the APD2000 and a modified ICAM for domestic preparedness.

An excellent source of information for first responders interested in equipment is the responder knowledge base Web site: www.rkb.us

For excellent patient education resources, visit eMedicine's Bioterrorism and Warfare Center. Also, see eMedicine's patient education articles Chemical Warfare and Personal Protective Equipment.