Personal Chemical Warfare Agent Monitors: Ion Mobility Spectrometry (IMS) Detection

Introduction

In my previous posts (here and here), I introduced the idea of “Personal Safety” equipment as part of a CBRN operator’s basic kit for most/all missions. This series builds off the ideas I’ve written about previously as part of a target-based approach to CBRN operations, see here:

• An Alternate Approach to CBRN Operations

• Following Captain Obvious: A guide to CBRN operations against obvious targets

• Don’t Break the Beaker: CBRN Operations Against Small Scale Production Facilities and Laboratories

• CBRN Operations and Industrial Scale Production/State-Sponsored Programs

• Proving the Negative and Cleaned Sites

To review, the basic “personal safety” kit for CBRN operators consists of:

• An adequate level of PPE (see the previous post for a full discussion)

• A gamma/neutron radiation monitor and dosimeter (see the last post for a full review)

• An air monitoring instrument for confined spaces

• A personal chemical agent detector/alarm (Optional, depending on mission requirements)

In this post and the next, I’m going to look at ways CBRN operators can best select and use chemical monitors, both chemical agent detectors and Multi-gas monitors for confined spaces and general air monitoring. I’ll also discuss some of the ways CBRN operators misuse this equipment and techniques to correct those deficiencies. This post looks at Chemical Warfare Agent Monitors (specifically IMS based detection). In the next post, I’m going to look at the most misunderstood, misused, and poorly trained pieces of equipment in all CBRN world: the ubiquitous multi-gas monitor.

Chemical Agent Detection

Before discussing the selection and use of chemical warfare agent (CWA) monitors, it is vital to understand the technologies behind the two most commonly used air monitoring devices in CBRN operations. While there are a variety of technologies used for chemical vapor detection, most of which I will address in later posts in this series, the most commonly used in a “personal protection role” are the following:

• Ion Mobility Spectrometry (IMS)

• Electrochemical Sensors

• Catalytic Bead Sensors (CAT).

  • NOTE: A type of Combustible Gas Indicator (CGI), a CAT is just one kind of CGI and the most common CGI found in confined space monitors.

• Photo Ionization Detectors (PID)

Some of the newer devices on the market incorporate other technologies or multiple technologies, but these are the most commonly used in personal detection/monitoring. Additionally, colorimetric and more passive devices (Colorimetric Paper, Tubes, etc.) are also sometimes used in personal protection. I am not going to talk about now but will address in later posts discussing other monitoring and detection instruments, sampling, and hotzone operations.

The first technology (IMS) is the most widely used in military chemical warfare agent (CWA) detection. The overwhelming majority of chemical agent detectors and area monitors in western military units (not just CBRN units) are IMS based. For most CBRN units in the US military, the piece of IMS based equipment they use in a personal detection role is either the M4 or M4A1 Joint Chemical Agent Detector (JCAD).

The second (electrochemical sensors) and third (CGIs/Catalytic Bead Sensors) technologies are ubiquitous in the chemical industry in a variety of general and specialized applications. The ones most familiar to the CBRN/HazMat community are the four sensors required for a confined space entry. These consist of three Electrochemical sensors, Oxygen (O2), Carbon Dioxide (CO2), and Hydrogen Sulfide (H2S), and one combustible gas indicator for Lower Explosive Limit (LEL). Many CBRN and HazMat organizations use these in combination with a Photo Ionization Detector (PID) in a single instrument. Within US military CBRN organizations, this is often a Multi-Rae or similar device.

Ion Mobility Spectrometry

Technology

As noted, the most widely used technology for the detection of Chemical Warfare Agents (CWAs) is Ion Mobility Spectrometry (IMS). The reasons for this simple, it is fast, has a low false-negative rate, and the technology involved is small, rugged, and mature. Developed and first issued to the military in the 1970s, IMS is definitely “old school.” Further, IMS devices require little power to operate, and IMS has exceptionally high sensitivity to low concentrations of some of the significant agents of concern (H-Blister and G-Nerve). Of course, any experienced CBRN operator will quickly note its most significant disadvantage: IMS has a high false-positive rate.

That last factor often leads to dismissive attitudes toward IMS based detectors in the CBRN community. That is a mistake. IMS detectors are extraordinarily useful in CBRN operations. You need to know when and how to use them! The key to understanding how to use them is understanding the way the technology works – which is quite simple. Also, users must know that the opposite of the false positive rate, a low false-negative rate, can work to your advantage if you understand when and where to use IMS. If other things point to CWA, additional tests (colorimetric, etc.) give you a positive result, and the IMS says CWA, you can have confidence in the result.

Traditional IMS works using a small air pump to draw in a sample of air near the detector. This sample then passes over an ionization source, traditionally a radiation source (usually Nickel-63 or Americium-241), that ionizes the air sample. Newer systems like the JCAD use other ionization sources, but they work the same way. These different technologies for ionizing the source include photon, corona, and flame ionization, but older IMS detectors for CWA detection use radiation because it is simpler, more rugged, and safer than other options, though the trend is away from radioactive ionization due to the need for wipe tests and regulatory licensing requirements.  

After ionization, the IMS device passes the ionized sample molecules through an ion gate and directs the ionized molecules present in the sample down an electromagnetic “drift tube” carried within a drift gas. At the back end of the tube is a Faraday plate, which detects the ions as they reach the end of the drift tube. The drift tube is the “Ion Mobility” part of the detector: ions with greater mass travel slower down the tube, while “lighter” ions move faster. By calculating the time of flight (TOF) for each ion and the intensity of its neutralization on the detector, the presence of specific sized molecules is detectable, given their known travel time and intensity (that’s the spectrometry part).

There are additional complexities related to pre-concentration of the air sample, the drift gases, tube length, temperature and pressure control, and reagent gases or dopants, none of which are necessary to understand the basic principles of operation (if you want to know more, this article offers more of the nitty-gritty science stuff, or try this one for a somewhat lighter explanation). Because the certain known CWAs fall within a certain range of masses when it comes to their molecules, their time of flight (TOF) and intensity are known. Field-portable IMS detectors work for most CWA purposes in environments otherwise clear of volatile organic compounds or other pollutants – if CWA is present, the detector alarms, if the air is clear, they do not. The problem is that because of IMS’s low selectivity (other molecules of comparable size have similar TOF/intensities), you have an incredibly low false negative, remarkably high false-positive problem with IMS. To put it another way, if it is a CWA agent (blister or nerve), the detector will almost always alarm, but it will alarm at a lot of other things too.

There are also different variants of IMS based detection: conventional Drift Tube IMS, as just described, Aspiration IMS (AIMS), and Field Asymmetric IMS (FAIMS), among others. IMS detection is also like TOF mass spectrometry, and some lab-based and newer portable instruments combine IMS detectors with a Mass Spectrometer or utilize Liquid Chromatography (LC) or Gas Chromatography (GC) to improve analytical capabilities. This latter development is important for many advanced explosive detection systems like those encountered at security checkpoints. Such combinations significantly improve selectivity and reduce the number of false positives but make for larger, more cumbersome devices poorly suited for the average military unit in the field. Further, such devices have a limit as to their current miniaturization that makes them unsuitable as personal detection devices – they are “man-portable,” not handheld. Handheld “explosives” detectors utilizing IMS have even higher false-positive rates than chemical detectors – because they have a broader range of detection. Another approach is to combine IMS with another detection technology like a Photo Ionization Detector (PID) or a Flammable Ionization Detector (FID), giving the device multiple inputs to analyze and potentially reduce false positives (or increase them depending on how they are set up).

Joint Chemical Agent Detector (JCAD)

For most military units in the US and some of its NATO allies, a personal CWA alarm is going to be a JCAD or JCAD equivalent IMS based system. Even if it isn’t something “JCAD like,” IMS is easily the most popular CWA detection system in most militaries. Do not confuse these, however, with systems like the ICAM or RAID-M 100, etc. Those IMS based “point detectors” have their uses in decontamination and specific mission profiles (like obvious missions). Likewise, JCADs are useful area monitors for area monitoring around a site (or other networked systems like AreaRAE), but that is not what I’m talking about here – same tech, different application. I’ll address those uses later, for now, I’m still talking about basic personal protective kit – something carried by CBRN operators for most or all missions.

The M4A1 Joint Chemical Agent Detector (JCAD), an IMS based detector whose fielding and development program suffered many issues going back two decades (and involving multiple contractors), finally entered service quite recently in the US military, beginning in 2016. The original M4 JCAD replaced three systems – the M22 Automatic Chemical Agent Detector and Alarm (ACADA), the M90, and M8A1 systems a few years before the M4A1 (about a decade ago, in the late 2000s). The Joint Program Executive Office – Chemical, Biological, Radiological, and Nuclear Defense (JPEO-CBRND) also proposed the M4A1 serve as a replacement for the Improved Chemical Agent Monitor (ICAM), a more traditional based radioactive IMS system, though ICAMs continue in service in many units.

Smiths Detection, the final contractor (following several others going back to the 1990s either due to contract changes or defense company mergers), now produces the M4A1. Manufacturers and developers made several claims over the years regarding the IMS technology in IMS detectors. Specifically, they often claimed their unique technology reduced the false positive problem (a claim BAE Systems made before Smiths). More recently, Smiths began marketing variants of the M4A1 as capable (with upgrades) of improved “Toxic Industrial Material” detection and even “Explosives” detection. Yet, with IMS, expanded detection does not necessarily mean better detection. Widening the range of detected ions means more false positives!

The M4A1 program replaces the original M4 JCADs with a new device using Smith’s analytical electronics and a built-in pre-concentrator. The most noticeable difference between the two (M4 and M4A1) is the replacement of the “GTH” indicator lights on the M4 (like those on the old M22 ACADA) with an LCD screen and controls. Otherwise, the two systems utilize the same mounting kits and other hardware.[1] The problem with this is easy to understand – a poorly trained operator selecting all of the monitoring options available on an M4A1 with the pre-concentrator is going to have a lot of false positives and may, over time, learn (wrongly) to ignore the system (a problem with the M4. ACADA, and all IMS predecessors).  Additionally, the M4A1 is not necessarily innovative technology – pre-concentrators existed on several previous IMS based devices, and the LCD screen is a return to developmental iterations of the M4 that worked the same way (BAE’s had one). It is more of an improvement on existing technology, to the point it can be improved. The main difference is on the analytical side, where the “electronics” reduce the false positives for some things, mainly increased sensitivity and faster signal processing. Even then, there is only so much that is possible with IMS. The technology is only capable of a certain level of specificity.

Operation and Use of IMS Detectors

While the JCAD replaced the ACADA as an “area alarm” for many units, it can also function as a point detector, though ICAMs (designed as a point detector) continue in service in some units, while non-US units and specialized CBRN teams may utilize Commercial Off the Shelf IMS or other detectors (like the Bruker RAID-M 100). The newest JCADs and systems like the RAID-M all move away from the more common radioactive ionization in older systems to non-radioactive ionization, including high energy photoionization (HEPI) and other systems. Using non-radioactive ionization sources reduces the need for regular wipe testing and radiation source licensing, eliminating a major maintenance headache for units.

The principles of IMS are the same, no matter the gimmicks, tricks, and technologies used. It is all about TOF and intensity at the Faraday plate. That means, even with tweaks like Smiths’ addition of a pre-concentrator and electronic analysis of the signals and time of flight or other tricks involving unique designs for the drift tube, dopants, ion traps, or carrier gases, you still have a false negative problem, especially when you monitor for “TICs and Explosives” – which widen the range of detected molecules based on wider TOF and intensity ranges. Further, TIC/TIM detection has a greater false negative problem than with CWA detection. Such IMS based alarms work “good enough,” they are incredibly dependable at telling you “something is here” and that something “resembles” nerve, blood, blister, “TIC/TIM,” or explosives, but that result is not definitive. It is information that allows units and individuals to act by taking protective measures until they determine why the alarm is going off. The problem is, if it goes off all the time, people start to tune it out!

Worse, poorly trained units may not comprehend that a TIC/TIM alarm does not mean their protective mask filter will protect them against the vapor present (a common mistake in regular line units and some non-specialized CBRN units.) Air-purifying respirator (APR) filters are chemical and concentration-specific, and while a standard NATO filter is effective in a lot of cases, it does not protect against all threats or concentrations. That, however, is not an equipment issue, but a training and education problem.

Older CBRN hands know the tricks to make an IMS detector alarm, the simulants used varied depending on the equipment, but much of it was readily available, from permanent markers to brake fluid. Other things (like vehicle or generator exhaust) could also set off IMS alarms like the M22 ACADA. Such problems led many in the CBRN world to discount the systems, and they earned a negative reputation, especially devices like the APD2000 and other systems marketed widely, seldom used correctly, and prone to multiple issues.

So, why use an IMS based detector? The answer is simple – if you are operating in an environment or on a mission where the threat of encountering CWA is high – you want one, especially if your initial entry is at a lower level of personal protection. It gives you a heads up you might not get otherwise. Does that mean you take it as gospel that when it goes off, it is detecting what it says it is? Nope, to quote the arms control crowd, “Trust, but verify.” That’s why understanding your mission is vital. The JCAD is excellent for mounting on vehicles, along a perimeter, or as an area alarm in a combat arms unit conducting operations against an enemy that possesses a chemical warfare capability (Russia, North Korea, Syria, etc.). Developed specifically as a personal alarm, IMS performs well when a CBRN unit operates in places where they may run across CWA – ammo bunkers, clandestine labs, CWA IED emplacements, etc.

However, IMS is not the be-all-end-all of CWA detection. It is best for “obvious missions,” to use the target-based approach to CBRN operations I’ve described elsewhere. If you need to detect something IMS can detect, its best to use an instrument designed to detect that, and if possible put it into an operating mode that detects only that. For example, most combat arms units ought not to use the explosives/TIC-TIM options in most area monitoring scenarios, unless there is a specific need to do so, or they like false positives for some silly reason. For example, when assessing potential chemical artillery rounds, a JCAD is a vital thing to have (along with other stuff like M8 paper). On the other hand, if you wander around a refinery, IMS detectors in a “TIC/TIM” mode are not going to help you, unless you enjoy constant ear-piercing alarms. Even in some clan lab scenarios, you may wish to turn it off, even if you still take it with you should the need arises to use it. Though, as a reminder, turn on all air monitoring instruments in “clear” air and “bump test” them regularly and, if possible, before operation.

An IMS system is also useful in a “general warning” role at its highest sensitivity, with pre-concentrator and “TIC/TIM” mode alerting you of toxic vapors if you are operating with no/low Personal Protective Posture – it tells you to put a mask on, or maybe consider upgrading from mask/APR to SCBA. In that role, IMS is useful in some Sensitive Site Exploitation missions where you don’t expect to find toxic vapors. It acts in a similar role to radiation monitors, as discussed in my previous post. It’s a “heads up” alarm that lets you know it is time to put a mask on and re-evaluate. It is not perfect, though, IMS needs a certain level of vapor present in the air to function. Some agents (blister, VX) have much lower volatility, and that volatility tends to decrease at lower temperatures, another factor to keep in mind when using an IMS detector in the “area,” “personal,” and “point” roles. IMS can also take some time to clear once it alarms, another issue when operating in contaminated environments.

The biggest problem for IMS and systems like the JCAD is the emergence of novel threat agents. The Russians developed “fourth-generation agents,” more generally known by their Russian name “Novichoks,” and may have ongoing CW development programs outside of the OPCW inspection regime. As used in the Salisbury, UK attack, these new agents have extremely low volatility, delayed action, and may go undetected by current technology, to include IMS. The challenge presented by such agents for the CBRN world goes well beyond the inability of current IMS detection to detect them, however, as the Russians are believed to have developed other agents beyond that known publicly due to their use in the UK, complicating all CBRN detection. However, that is a separate issue and one I’ll talk about more in a later post.[2]

I’m also going to talk more about using chemical agent detectors to assess a CBRN scene in a later post, but for now, just remember that an IMS based personal alarm is part of the basic kit any time your mission assessment includes potential CWA or other toxic vapor, or when you need early warning to upgrade PPE for any reason (If you broaden the detection to include TIC/TIM mode). A JCAD or other personal CWA detector is unnecessary for a purely radiological mission (not that some “doctrinaire” type units don’t carry them anyway). In other words, it is advisable to not standardize their use. Rather, a personal CWA alarm is good when you have an idea of the threat level, and know what you want to detect (which will determine whether you take it, and what operating mode you put it in). The best role for IMS is the one that led to its development in the first place: alerting you of a condition where you need to adopt a higher level of protection, especially airway protection.

In the next decade or so, CBRN detection in the US military is going to undergo a notable change, away from single systems based on IMS to four distinct systems under the umbrella of the “Next Generation Chemical Detector (NGCD).” The NGCD program is a massive upgrade in CBRN detection and analysis across the force and represents a major departure from past systems. The systems will offer a modular, Milspec set of systems akin to the Commercial Off-the-Shelf (COTS) systems now employed by advanced CBRN units like Civil Support Teams or Tech Escort. See here for more. JPEO-CBRND expects Initial Operational Capability in FY2023 for the Aerosol Vapor Chemical Agent Detector (AVCAD) component of the NGCD, with fielding to follow later in the decade. JPEO-CBRND projects other components (PCAD, CVCAD) to achieve IOC late in the 2020s and into the 2030s. While the new suite of systems marks a serious upgrade in US CBRN detection capabilities, it will also come with a much steeper learning curve - these systems are not “grunt proof” and will require a significantly higher degree of education, training, and sophistication for proper use. Based on the implementation of GC/MS systems in the Fox and numerous examples of their misuse in the early 2000s, I am not hopeful that the Chemical School will adequately prepare CBRN soldiers for these changes in the short term, but I expect them to eventually get it right.

Digressions aside, I want to offer a few final notes on using IMS in a personal protection role, even though I’ll be going more into depth on using detectors/monitors in a later post. Operators should carry individual IMS monitors like the JCAD as close to the input of any Air Purifying Respirator as possible (usually mouth/filter level) but need to adjust their position if using a Powered Air Purifying Respirator (PAPR). Most CBRN units attach them at a chest level, but this may not be the best place when wearing a PAPR mounted on the back or at the waist.

Many of IMS devices like the M4A1 can also function as area monitors. In that role, for instance, an operator who is working around CWA may wish to detach the device and place it somewhere downwind, for example, instead of monitoring themselves for something they already know to be present, monitoring for unintentional releases produced by their operation.

In the point detection/identification role, operators need to take care to avoid overloading their IMS as they may take time to “clear,” especially if they are using a pre-concentrator. To avoid creating clearance problems during operations, bring the agent to the monitor, rather than the monitor to the agent if there is a significant quantity of agent present (especially visible liquid). In those cases, an operator may wish to take a “wipe sample” or a swab sample and hold it near enough to the device input to obtain a result (without touching/contaminating the device). That way, they can then remove the sample from proximity to the IMS input and allow the device to clear without overloading it and creating internal contamination or filter problems.

IMS, like all air monitoring instruments, can suffer degraded performance or even damage in different environmental conditions. Moisture is never good for any air monitoring instrument, and air pressure, humidity, and temperature all factor in when detecting toxic vapors in air, both in the ways they affect the instruments and the way they affect the agent. CWAs do not volatilize equally. Some, like mustard, don’t volatilize well at all, especially at lower temperatures. Others, like Sarin, volatilize quickly, especially at elevated temperatures. A few CWA agents fall somewhere in between (VX, for example). You have to know when and where to use air monitors and know about agent behavior, no matter if you are using IMS or some other detection equipment. Further, you need to take the weather into account. For example, I’ve seen “evaluating organizations” (US Army North/Fifth Army, cough, cough…) instruct units to put out IMS area detection and turn it on in heavy rain for “evaluation purposes,” thus deadlining all of a unit’s equipment. Even if you use covers or other devices, drenching rain will toast any air monitor eventually. Don’t do that, please. (As a side note, if you don’t know the “dixie cup” trick for protecting an air monitor input from (light) rain, I’m going to explain it in my next post, so stay tuned.)

Finally, IMS is useful in CBRN operations where operators suspect CWA contamination, to conduct both “smart decon” (that focuses on removing contamination) and in more traditional gross decon methods to verify completeness of the decontamination process. Decon units may use IMS detection on both ends of a decon line, but in CBRN operations with limited time or resources due to operational constraints, a CBRN operator can also use their CWA monitor to check for contamination after exiting a hotzone where CWAs were present or suspected.  IMS detectors allow operators to determine what they might need to abandon/destroy/burn on-site, help identify areas to avoid cross-contamination during PPE removal and areas to target with more limited decon efforts (wipes, etc.).

Summary

Personal IMS based chemical agent monitors make sense for many CBRN missions (and some CBRNe missions as well). However, IMS technology suffers from some inherent limitations, particularly as it relates to the false-positive problem. Offsetting those limitations is the low false-negative advantage. Understanding how, when, and where to use IMS based detection is a critical skill for CBRN operators, and one I’ll discuss again in a later post.

The use of IMS as a personal protection device is most important in traditional battlefield operations where there is the potential for CWA use and in CBRN operations where the likelihood of encountering CWA is reasonable, but not necessarily expected, allowing operators to increase their Personal Protective Equipment Posture/MOPP Level accordingly. IMS detection is also useful as a “point detection” source to obtain initial identification or confirm what other instrumentation or indicators suggest.

Despite its issues, IMS remains a critical technology in CBRN operations, and until something better comes along, it will remain the predominant CWA detection technology across different CBRN units worldwide. It does have significant limitations, though, and requires additional verification in the event of an alarm. Further, it has both “general” and “specific” detection and identification capabilities that vary in their utility. Lastly, IMS may or may not detect all CWA the same or as well as it did in the past, especially as evidence grows of novel forms of CWA (like Novichoks), an increasing concern going forward until newer detection equipment enters service. Even if IMS has lower false negatives than some other forms of detection, it still has false negatives.

In my next post, I’ll dig into multi-gas monitors. Multi-gas monitors are the most common air-monitoring devices in CBRN and HazMat operations, but also arguably the least understood and most often misused. So, that post will be a fun one that keeps close to the title of this series “I don’t think you are doing that right…”

Until then, if your CWA monitor does alarm, remember: Keep calm and decon!

Sources

Ion-mobility Spectrometry at Popflock (Note: While this article draws pretty heavily from Wikipedia, it is still pretty accurate and useful, and easier to read than some of what is on the Ion-mobility spectrometry Wikipedia page. While both aren’t as bad as some stuff at Wikipedia, the usual “this is a wikipedia article beware” cautions apply).

Makinen, Marko A., Osmo A. Anttalainen, & Mika E. T. Silanpaa, "Ion Mobility Spectrometry and Its Applications in the Detection of Chemical Warfare Agents," in Analytical Chemistry 82 (2010): 9564-9600.

JPEO-CBRND Page on New Detectors

US Army Weapons Systems Handbook 2018, pages 28, 176-177, 234-235, 278-279

Smiths Detection JCAD M4A1/LCD 3.3

G.A. Eiceman, Z. Karpas, H.H. Hill, Jr. Ion Mobility Spectrometry, 3rd Edition (Routledge, 2016)

W. Alexander Donal & James Prell, Advances in Ion Mobility-Mass Spectrometry: Fundamentals, Instrumentation, and Applications, Volume 83 of Comprehensive Analytical Chemistry (Elsevier, 2019)

Larry A. Viehland, Gaseous Ion Mobility, Diffusion, and Reaction (Springer, 2018)

NOTES:

[1] It is worth noting that the original version of the JCAD developed by BAE systems in the 1990s and early 2000s used an LCD screen and controls as well. The M4 as eventually fielded late in the 2000s/early 2010s went back to an indicator system like that of the ACADA and ICAM. We’ve now come full circle as the M4A1 while operationally different, looks quite similar in use to the original designs. The M4 (and its predecessor) also suffers some issues in VX detection, a problem the M4A1 remedies to some degree.

[2] The revelations regarding Novichoks in the 1990s were generally ignored due to a desire by the OPCW and other governments to keep a lid on the issue and push ahead with the Chemical Warfare Convention treaty despite the evidence the Russians continued to work on chemical warfare. If you want to know more, you can read the very idiosyncratic book by Vil S. Mirzayanov, though the original disclosures date from 1992, when Andrei Zheleznyakov, a Soviet CW scientist, fatally exposed himself to the agent by accident and revealed it to a Russian newspaper in 1992.