The ideal technology for detecting the presence of chemical agent, verifying that an agent is present, and identifying that agent would accomplish all three sufficiently quickly for threatened personnel to don appropriate
protective equipment before they are affected by the agent. Unfortunately, the current state of the technology is such that all three tasks cannot yet be accomplished within that relatively short length of time. Thus, the challenge is usually broken down into several components: individual detection, point detection, and subsequent identification and verification.
Disclaimer: this page is not intended to be an exhaustive list of all systems currently fielded by the US military. Rather, it provides a selection of systems sufficient to give an overview of detection, identification, and verification along with an indication of some of the underlying technologies.
Detection of Chemical Warfare Agents by Iindividual Soldiers Individual detection technologies provide the first warning of the presence of chemical agent. These technologies must be simple, light, and portable, so that they can be issued to many individuals, and fast so that they give an immediate warning of the presence of a chemical agent. The first warning of a chemical attack on the battlefield is often direct observation by well-trained troops of agent clouds and liquid fall out, as well as characteristic odors of certain chemical warfare agents.
Detection Paper The US Army issues M8 and M9 detection papers. These papers are impregnated with agent soluble pigments or dyes. The M8 paper gives immediate, qualitative verification of the presence of liquid V- and G-type nerve agents and H-type blister agents. The M9E1 tape, which can be worn on the uniform, detects the presence of liquid V- and G-type nerve agents and H- and L-type blister agents. However, detection papers are not as reliable as other means of detection because they depend on liquid agent contacting the surface of the paper; neither type of paper detects traces of chemical agent vapors. Some solvents and standard decontaminating solutions cause false-positive reactions by the M8 paper. Extremely high temperatures, scuffs, or certain types of organic liquids and decontaminating solution number 2 cause false-positive reactions by the M9 paper. The M9 paper does not distinguish between the types of agent involved only that an agent or agents may be present.
Detection Tubes In these systems, a small manual air pump draws air through a tube impregnated with an indicator which absorbs agent. The tube then requires the addition of a developer for verification.
Detection Kits
- The M256A1 Chemical Agent Detector Kit is a portable, disposable chemical agent detector kit that can detect and identify nerve, blister or blood agent vapors. It is typically used to determine when it is safe to unmask after a chemical agent attack. A test disk contains a glass ampoule with compounds that react with agent to give a color change. The ampoule is crushed, the activated test disk is exposed to the ambient air, and the disk is compared to a color chart to determine if agent is present.
- The M18A2 Chemical Agent Detector Kit uses both detector tubes and paper tickets to detect and classify dangerous concentrations of lethal chemical agents in the air, as well as liquid chemical agent contamination on exposed surfaces. Agents detected are: CK, H, HN-1, HN-3, CX, AC, CG, L, ethyl dichlorsarsine, methyl dichloroarsine, the G-series nerve agents, and VX. At present, there are no packaged detection kit systems for the arsenical vomiting agents, tear gases, and incapacitating agents.
All of the individual detection devices are simple and very sensitive and thus give a very rapid response. The drawback to the simplicity is that these devices generally do not identify the specific agent that is present; the drawback to the sensitivity is that these devices can give false positive readings. Therefore, separate systems are needed to verify the presence of agent and to identify the specific agent.
Point Detection Devices
The next step up in complexity and reliability comes in point detection devices. These devices also provide the first warning of the presence of chemical agent, but are generally used at a single location for a longer period of time. These technologies must be portable, but they do not need to be as light or as simple as detection device issued to individuals; the devices do not need to move as often and are operated by personnel with more specific training. The point detection devices are still required to be fast, so that they give an immediate warning of the presence of a chemical agent.
Battlefield Devices
- The hand-held Improved Chemical Agent Monitor (ICAM, also known as CAM2 TM) is based on ion mobility spectrometry(IMS). Air is drawn into the IMS unit and is ionized by a weakly radioactive source. Agent molecules in the vapor phase form low-mobility ionic clusters. These time of flight of the ionic clusters from a sample in a drift tube is measured relative to a reference cluster. A computer examines the pattern of the time(s) of flight in a sample, determines the level of chemical agent present, and indicates on a display or by an alarm the level of hazard.
The Automatic Chemical Agent Alarm (ACADA) system is another detector based on the GID-3 TM IMS. This system is a larger, man portable IMS system with a communications interface to support battlefield automation systems.
ACADA replaces the M8A1 Automatic Chemical Agent Alarm System, which was used during the 1991 Gulf War. The M8A1 is also portable chemical agent alarm based on IMS.
Long Range Stand-off Devices
The M21 Remote Sensing Chemical Agent Alarm (RSCAAL) is based on a passive infrared (IR) detector. The incoming IR signal is compared against known agent spectra; when a match is detected a display lights and an alarm sounds. The display also indicates in which of the seven fields of view (spread over a 60 degree arc) the agent was detected. This allows the operator to actually track a moving agent cloud. The M21 is capable of detecting nerve and blister agents in the vapor phase from a distance of up to 5,000 meters; however, it must have a direct line of sight to the agent cloud in order to function.
All of the point detection devices are very sensitive and thus give a very rapid response. Again, the drawback to this sensitivity is that these devices can give false positive readings. Therefore, separate systems are needed to verify the presence of agent and to identify the specific agent.
Chemical Agent Depot Systems
Two detection technologies are used at chemical warfare agent depots and demilitarization plants. The first of these systems is similar to the point detection systems, in that it is automated, rapid, and sensitive. The second system is used to verify the results obtained with the first; it requires sampling and subsequent analysis at an on-site laboratory.
- The Miniature automatic Continuous Agent Monitoring System (MINICAMS TM) is an automated near real time gas chromatograph. An air sample is drawn through a pre-concentrator loop filled with an adsorbent. Periodically, the system is switched so that a carrier gas stream flows through the pre-concentrator loop as it is heated, carrying the adsorbed sample into the gas chromatograph(GC). While the sample is analyzed on the GC, the pre-concentrator loop begins to collect the next sample. The GC separates the chemical compounds in the sample based on differential partitioning between the carrier gas and the stationary phase in the GC column. MINICAMS detects agent with a Flame Photometric Detector (FPD), which specifically detects the chemiluminescent reactions in a hydrogen/air flame of compounds containing sulfur and phosphorus. The entire cycle from sample collection to detection typically requires 3 to 5 minutes. MINICAMS is a refinement of the larger Automatic Continuous Agent Monitoring System (ACAMS) detector; ACAMS is still in use in some locations.
- Depot Area Air Monitoring System (DAAMS) is a system used to confirm the detection of agent by MINICAMS. Larger air samples are drawn continuously through the DAAMS tube, which contains a correspondingly large quantity of adsorbent. At either a pre-determined time, or when a confirmation of a MINICAMS is required, the DAAMS tube is physically transported to the laboratory, where the sample is desorbed into a laboratory gas chromatograph.
Identification and Verification
Identification and verification of chemical warfare agents can be conducted in the field, using mobile systems, or samples can be collected for subsequent laboratory analyses.
The M93A1 Fox Nuclear-Biological-Chemical Reconnaissance System (NBCRS) Vehicle
The M93A1 Fox is a self-contained mobile system equipped with the M21 Remote Sensing Chemical Agent Alarm, a passive infrared detection device, as well as with the MM-1 Mobile Mass Spectrometer.
The mobile mass spectrometer is capable of identifying and verifying chemical warfare agents in samples. The mobile instruments used in the Fox are by nature a bit less sensitive and selective than the instruments used in a fixed laboratory because they are generally limited in their size, weight, and power consumption relative to their laboratory cousins, and must be built to withstand a higher level of vibration. However, the lower sensitivity and selectivity are offset by the fact that the Fox can be driven to the site of a chemical attack, so that no time is required for the sample to be shipped from the site to the laboratory.
Sampling in the Field
The most certain method to positively identify a chemical warfare agent and to verify its presence is analysis in a state-of-the-art laboratory. Once an individual or point detection device sounds the alarm, and the appropriate protective equipment is donned, physical samples can be collected and shipped to the laboratory. In addition to its use for immediate detection, the M18A2 kit is also used to collect and forward samples of unidentified chemical agents to a laboratory for identification.
The drawback to sampling and subsequent analysis is that it takes a significant amount of time to ship a sample to the laboratory; at best, days will elapse from the time the sample is taken until the results are reported. Thus, this procedure is generally reserved for collecting intelligence about the use of chemical agents, rather than for immediate health and safety protection.
Laboratory Techniques
Analytical techniques in common use in the laboratory include:
- A gas chromatograph(GC) separates the chemical compounds in the sample based on differential partitioning between the carrier gas and the stationary phase in the GC column, then detects agent with an FPD. The underlying technology is the same as that used in MINICAMS; a laboratory GC has a longer, thinner column and operates at different temperatures. The laboratory instrument requires a longer amount of time for the analysis, but it provides a better separation of the compounds in the sample and the analysis takes place in a cleaner environment, so it is less prone to interference than MINICAMS.
- Gas chromatograph/mass spectrometry (GC/MS) uses a GC to separate the material in a sample into relatively pure chemical compounds, then uses the MS to identify the substance. The MS ionizes the compounds, and the ion then fragments; the instrument then measures the mass-to-charge ratio of the fragments. The distinctive fragmentation pattern serves as a molecular fingerprint that identifies the structure of the compound.
GC and GC/MS are used for the bulk of routine analyses of samples that may contain chemical warfare agents. These techniques afford a very low rate of false positives and false negatives, and are capable of providing definitive identification of the chemical agent that is present.
Other technologies that are used in frequently, or are currently being developed include:
- Liquid chromatograph/mass spectrometry (LC/MS) uses an LC to separate the material in a sample into relatively pure chemical compounds, then uses the MS to identify the substance. It is more sensitive than GC when less volatile substances are analyzed.
- Nuclear Magnetic Resonance(NMR) spectrometry measures the absorbance of radiofrequency energy by a sample in a magnetic field. NMR gives a spectrum that is a molecular fingerprint of the chemical compound.
- Ion chromatography(IC) separates ionic substances on an ion-exchange column; it can be used for measuring the substances produced by environmental degradation of some agents.