Decision-making in CWA response

CarolinaFireJournal - Chris Wrenn
Chris Wrenn
01/11/2010 -

In responses to releases of Chemical Warfare Agent (CWA) there may not be one technology or one “answer” that is correct. The responder must take into account all of the clues present to conclude the presence or absence of CWAs and take appropriate action. Understanding what the clues are and how to layer them to make a decision is critical to successful CWA response.


(This is part two in a three-part series on gas detection.)

Biological detection

A nerve agent will kill other species too, and dosage is dependent on the size and the metabolism of the animal. Smaller animals with fast metabolisms will be affected faster than large animals with slower metabolisms. Insects, amphibians, reptiles, birds and small mammals will all be affected by nerve agents before humans. However, humans are biological indicators for large animals like horses and elephants. Because of its low vapor pressure and high vapor density, nerve agents will not stay aerosolized, meaning they will quickly fall to the ground, affecting ground dwelling and grazing species first.

Nerve agent symptoms

There are two major mnemonics used to remember human (and animal) nerve agent symptoms: DUMBBELLS and SLUDGEM. Each captures many of the same symptoms somewhat differently.


D - Diarrhea (Diaphoresis-excessive sweating)

U - Urination (peeing)

M - Miosis (constriction of the pupil of the eye)

B - Bronchospasm (difficulty breathing)

B - Bradycardia (slow heart beat)

E - Excite skeletal muscle and CNS emesis (vomiting)

L - Lacrimation (tearing)

L - Lethargy (fatigue)

S - Salivation (excessive drooling)


S - salivation (excessive drooling)

L - lacrimation (tearing)

U - urination

D - defecation / diarrhea

G - GI upset (cramps)

E - emesis (vomiting)

M - muscle (twitching, spasm, “bag of worms” )

Severity of symptoms is dose dependant

  • Nose:  runny nose (Rhinorrhea)
  • Airways:  tightness in chest, difficulty breathing, wheezing (Dyspnea)
  • GI Tract:  nausea, vomiting, diarrhea
  • Glands:  increase of secretions sweat, nasal, salivary, bronchial
  • Skeletal:  muscle twitching
  • Central Nervous System (CNS):  confusion, agitation, forgetfulness, insomnia, irritability, impaired judgment, seizures, coma
  • Eyes: pinpoint pupils (Miosis )

“The eyes may be the window to the soul, but they also can serve as an agent alarm,” (i.e. miosis) (Brad Rowland, DPG)

CWA Accessibility

Abandoned munitions and lab materials at military or research facilities can provide easy access to CWAs. The number one way to dispose of chemical munitions up until the last few years, was to bury and forget them.Because of this, we have lost track of some. CWAs can be stolen from poorly maintained regulated stockpiles.  CWAs can be obtained from former war zones. Terrorists in Iraq and Afghanistan have used CWAs as IEDs, either intentionally or inadvertently. Finally, Aum Shinrikyo has twice demonstrated that they can make and disperse Sarin and it can be expected that others can and will follow Shinrikyo’s example.

Dissemination is the key

If one were to solely look at CWAs chemical characteristics they would not appear that threatening. While they are very toxic, they don’t want to move and “chase” you as gases like chlorine and ammonia can, and will do. The key to successful deployment of CWAs is dissemination, which is a fancy name for the technique used to spread the CWAs around.  There are four disseminations techniques and they can provide a clue as to the nature of the attack/event:

1. Explosive Dissemination

  • The military has honed their skills on using low level explosive (dispersant) charges to disseminate chemicals.  A CWA shell is lofted into the air by its propellant charge.  When it reaches the proper altitude, a secondary “dispersant” charge is detonated to turn the heavy liquid into a mist or a spray that spreads out over the opposing military.
  • Big explosions burn up chemical like a fuel-air bomb, but small ones spread it effectively.  So if witnesses/victims talk of hearing a “pop” without a fireball that is a good sign of a dispersant charge.  If they speak of a big boom or whoomp followed by a fireball it is highly probable that the explosion consumed the CWA.

2. Pneumatic Dissemination

  • Can be as simple as garden sprayers.  Shinrikyo’s first strike was against judges in Masumoto, Japan using a sprayer that killed seven.

3. Mechanical Action Dissemination

  • Plastic bags inside paper bags or boxes that were poked with sharpened umbrella tips in Tokyo proved to be a poor dissemination method. This seems to indicate that their intent may have been to create more of a distraction than to kill large numbers of people.
  • Glass bottles dropped from above may be relatively effective.

4. Chemical Reaction Dissemination

Cyanide tablets plus acid = gas

Dissemination is the key to killing a lot of people. With proper dissemination, Tokyo could have been the first 9/11 type event with thousands of fatalities. Poking holes in plastic bags using sharpened umbrellas was not effective in killing large numbers of people, but it did create panic amongst thousands.

Why are survey sensors

Survey sensors or “sniffers” are one of the best tools to quickly identify if something is out there and where it is located. On their own, survey sensors will not tell you what that “something” is, but they can often quickly, within less than three to 10 seconds, tell you where it is coming from and give you a quick idea of how much is there. “Classification” and “Identification” devices may be too slow to “sniff.”  

PIDs and FIDs

A PID will provide faster “sniffing” for the location of CWA than most CWA detectors because it not only responds faster but it will display below the alarm threshold so that concentration gradients can be “seen.”   CWA detectors often require more time to detect, therefore when sampling, the user often must check for potential contamination slowly and methodically, much like when checking for alpha radiation contamination. Coupled with clues (like chemical pools, clouds, dead animals, victims, placards and waybills, etc.) that provide identification of a chemical, some survey sensors like Photoionization Detectors and Flame Ionization Detectors (PIDs & FIDs) can quickly tell you how much is there when the proper scaling factors (Correction Factors) are used.


  • Relatively inexpensive to purchase
  • Can detect CWAs in air
  • Fast response time
  • Store well
  • Inexpensive to use at less than $0.25 per hour for PID and less than$1 per hour for FID


  • PIDs and FIDs are non-specific

M9 tape

M9 is a “dumb” survey technique. M9 tape is a simple colorimetric technology.  It is designed to be taped to personnel (on boots and the bottom of pant legs) and to vehicle bumpers. It only indicates red as a positive response and is best used with a classification technology. 


  • Simple
  • Stores well (keep cool)
  • Inexpensive at less than $7 for a 10m roll


  • A liquid sample is required
  • Red color change can’t be read with night vision filters (red) on flashlights
  • Many organics will provide positive response,  including cleaning solvents, ammonia, some petroleum products and even high temperatures.

Locate THEN classify

A PID in the hands of a person trained in identifying CWA signs and symptoms may provide faster screening in a decon line than a CWA detector because no handheld CWA detector can detect below miosis levels. You can see it in their eyes before you can detect it.  Locate first, then classify. 

CWA classification

Classification will typically take more time than location. Classifiers will typically come up with an answer quicker on real agent than on cross-sensitive chemicals.  There are two fundamental types of CWA classification techniques, chemical color change technologies (colorimetrics) and direct reading devices. Properly used in conjunction with each other and the other clues at a scene, these technologies can provide a very high degree of confidence.

M8 paper

M8 Paper is one of the simplest means of classifying CWAs. Some have called it “pH paper” for CWA. Detection is based upon solubility of dyes in CWA. Nerve indicates yellow, Blister indicates red and VX indicates green. 


  • Simple
  • Stores well (when kept cool)
  • Inexpensive at less than $5 a book


  • A liquid sample is required
  • Many organics will also dissolve the dyes including cleaning solvents, ammonia, some petroleum products and even high temperatures.

M256A1 kit 

The M256A1 kit is an organic chemistry set on a paper card to provide classification of nerve, blister and blood agent gas, vapors and liquids (an undocumented feature of the M256A1 kit is that drops of chemical samples can be put on the sample pads for faster response than waiting for an airborne sample). The test process takes 12 to 25 minutes and the instructions are complicated (and hard to read die to the dark green packaging material). It is counter-intuitive that the G series indication is a lack of color change where the other pads do change colors. Most colorimetric techniques make a positive color change in the presence of the target chemical. 


  • Cheapest way into vapor detection of CWAs ($140 per kit)
  • Can do liquids too
  • Stores well (keep cool)


  • 15 to 25 minute test time
  • Complicated instructions
  • “Trainer” kits are only differentiated from the real thing by a blue band around the dark olive green package. It is very hard to see.
  • Interferants: some smokes, high temperatures and petroleum products
  • Per use cost of $140 is high if multiple samples are required

Colorimetric tubes

Often referred to as “Draeger” tubes after the German manufacturer, a colorimetric tube is a glass tube filled with a silica substrate coated with reagent that will produce a color change when exposed to the chemical of interest. The user draws a predetermined sample through the tube and reads the scale like reading an old glass thermometer. The tube is calibrated at the factory and this calibration is printed on the side of the tube as a scale. Calibration is typically valid for operation life of tube (two years).  


  • Proven technology
  • Factory calibrated (no expensive calibration gas required)
  • Relatively inexpensive vapor detection technique ($2 to $10 per sample)


  • Snap Shots,” non-continuous, no alarms can result in sampling error
  • Respond in minutes rather than seconds
  • 15 to 25 percent accuracy Piston/Bellows style
  • Readings subject to interpretation
  • Does not store well, tubes expire and large stock is expensive to keep up to date (keep cool)

Traditional “Closed Loop” IMS

Ion Mobility Spectroscopy (IMS) uses a radiation source (ionizing and non-ionizing) to break down a sample into ions that then travel down a magnetic drift tube to generate a characteristic spectra or “picture.” This picture is matched up against pictures in the detector’s library to provide a positive identification. One simplistic way to look at IMS is “ion distillation.”   In traditional closed loop IMS the ion cell is separated from ambient air by a membrane to keep contaminants from affecting the signal.

Clean air, provided by a sieve pack, keeps the inside of the ion cell perfectly clean.  Sometimes chemical dopants are also used to keep contaminant under control. For example, acetone is used by one manufacturer to help absorb moisture. Membranes, sieve packs and dopants are expensive consumables that have to be periodically replaced (typically annually depending on use). Sometimes change out is predictable but they can fail unpredictably when presented with gross contaminants. The membrane slows response time, especially on VX, and also slows recovery when the detector is exposed to high chemical concentrations. Some closed loop IMS CWA detectors need to be “exercised” or run once a day/week/month or else they will not work when an emergency comes.  To “exercise” a detector, you turn it on, wait for it to stabilize, challenge it with simulant and then wait for it to clear.  This process can take over an hour.


  • Sensitive instrument good for vapor detection
  • Military proven technology
  • Quick response time
  • Good detection of class (i.e. G vs. H)


  • False positives to many common urban chemicals
  • Small to none TIC capability until $20-30K detectors
  • Some use radioactive sources that require NRC license and periodic wipe testing
  • Unpredictable maintenance intervals, if the sieve gets chemically contaminated it will not work
  • Membranes slow response time
  • Stores poorly, must be exercised
  • Can be expensive to maintain lifetime costs of +$2 per hour of use

Open loop or
“aspirated” IMS

The open-loop Ion Mobility Spectroscopy (IMS) sensor uses a Nuclear Regulatory Commission (NRC) exempt Am241 (Americium) ionization source. As safe as a smoke detector, it doesn’t require periodic nuclear wipe tests like Ni63 in some other IMS products. The IMS sensor is open to the environment, no membrane or sieve pack is used to maintain cleanliness in the sensor. Because of this the open loop IMS can provide much faster response and clearing times than closed loop IMS.  Life-cycle costs and logistical footprint are much less than those of traditional IMS and flame-spectrophotometer based devices because it doesn’t require costly membranes and sieves to keep the sensor clean and it doesn’t use expensive hydrogen gas. 


  • Sensitive instrument good for vapor detection
  • Military proven technology
  • Quick response time
  • Good detection of class (i.e. G vs. H)
  • Good TIC capability (~20)
  • As safe as a smoke detector
  • Predictable service intervals
  • Stores well, no need to exercised
  • Inexpensive to maintain, lifetime costs ~$0.33 per hour of use


  • False positives to many common urban chemicals (typically shown as a “Chemical Threat” alarm)

Surface acoustical wave (SAW)

SAW sensors convert acoustic waves to electrical signals by exploiting the piezoelectric effect of certain materials. Their use for CWA detection originated in the US Naval Research Labs.  A waveform (sound) is generated on a quartz substrate. The substrate is coated with a polymer that has an affinity with the chemical to be detected. When the target chemical bonds with the polymer coating, the wave form frequency changes (tone changes) indicating that the target chemical is present.  Selectivity comes from the choice of the polymer coating.  Simplified, a SAW is essentially a polymer (“paint” ) on a quartz substrate; the chemical of interest is absorbed into the paint and changes the tone. 

While an elegant solution, the problem with SAWs is chemical contamination of their polymer coatings. Consider a handprint by a light switch on the wall.  You clean the handprint (but if you have small children) it comes back. Eventually you no longer can clean the handprint and you have to repaint. As the paint (polymer) in a SAW absorbs chemical, some of that chemical (either target or interferant) is left behind.  As chemical is left behind the baseline signal rises. Eventually the baseline signal rises to the point that it equals the signal level and you cannot detect anymore and you need a new sensor and SAW sensors are expensive to replace.  


  • Very specific vapor detector
  • Proven technology
  • Stores well (assuming no contaminants in the air)


  • Some common vapors (like alcohols) may ruin the polymer coating
  • While specific, often don’t alarm until IDLH levels
  • Unpredictable end of life
  • Lifetime costs can be significantly higher than IMS based products ($2.40 per hour of use)

Flame Spectrophotometry

Flame Spectrophotometry detectors use a colorless hydrogen flame to burn the sample. Chemicals produce characteristic electromagnetic spectra (colors) when they burn. The detector looks for the spectra (colors) that are specific to sulfur and phosphorous compounds that are a defining characteristic of blister and nerve agents.  It quantifies by the intensity of the color. The  brighter the color the more chemical is present. It is very sensitive and quick to respond to chemicals that contain sulfur (blister) and phosphorous (nerve). However, this sensitivity to sulfur and phosphorous compounds can lead to cross-sensitivity and false alarms. Product manuals warn against locating near exhausts which can produce sulfur dioxide as a by-product of the combustion process and give a false positive for blister. Also, phosphorous isn’t just in organophosphates. One common use for phosphorous is a whitener in detergents. So if one doesn’t rinse their wash thoroughly a Flame Spectrophotometry detector could improperly identify detergent residue as nerve.


  • Military proven technology
  • Quick response time
  • Stores well, no memory affect


  • EXPENSIVE to purchase
  • False positives to exhausts, fuel spills and detergent
  • Does not measure TICs (unless they have Sulfur or Phosphorous in them)
  • Run time constrained by hydrogen size to 12 hours per cylinder (at $100 per cylinder)
  • Long term operations can be hindered by the requirement for hydrogen gas
  • Hydrogen gas is difficult to ship by air which hinders air deployment of this technology (hydrogen fill station costs $75K)
  • $9+ per hour to run

Orthogonal detectors

“Orthogonal” means to look at something from many different angles and orthogonal detectors do this by using a variety of sensors rather than just one type to come to a conclusion. Each sensor has its strengths and weaknesses.  “Sensor fusion” takes advantage of this by utilizing the strengths of a number of sensors to come to a final conclusion. Advanced signal processing is used to match the pattern from the sensor array to a library of compounds. By using multiple sensors the goal is to increase sensitivity while reducing false alarms. Another way of looking at this is that redundancy is built into the detector. 


  • Less false alarms
  • More chemicals detected than just a short CWA list
  • Great when they cost less or the same as the sum of the various detectors that they replace


  • Can be very expensive
  • Can be larger and heavier
  • Their value is questionable when they cost much more than the sum of the detection technologies they include

CWA classifiers can be fooled

CWA classification techniques were designed for the battlefield environment and do not always take into account cross-sensitivities from common chemicals found in the urban environment.  Low vapor pressure for most CWAs complicates classification because other low vapor pressure chemicals can fool the algorithms. This is not a condemnation of CWA classifiers, just a realization that multiple confirmational techniques may be required in CWA response.  CWA classifiers tend to take longer to come up with a solution when presented with simulants than if presented with the real thing. 

CWA simulants/cross-sensitivities for classifiers

  • Brake Fluid (nerve on some IMS)
  • Anti-Freeze (blister on some IMS)
  • Anything with Methyl salicylate (oil of wintergreen) including:  Skoal, Wintergreen Altoids, Peppermint Oil, Mennen “Speed Stick,” “Deep Heat,” Ben Gay, (blister on some IMS)
  • Detergent residue on clothing due to the phosphorous in “whiteners” (nerve-Flame Spectrophotometry)
  • Sulfur compounds in fuel products or exhaust (blister-Flame Spectrophotometry)
  • Fingernail polish remover (nerve-M8)
  • Cleaners that containing esters including:  “Super Gleam” glass cleaner, ACE Brand window cleaner, “Spray-9” industrial cleaner, (nerve on some IMS)
  • Real toxic materials (chemically similar to nerve)
  • Parathion (nerve)
  • DMMP:  Dimethyl Methyl Phosphonate (nerve)
  • TEP: Triethyl Phosphate (nerve)
  • Sevin (nerve)

(The last installment in the spring issue will discuss CWA identification.)

Christopher Wrenn is the Sr. Director of Sales and Marketing for Environics USA a provider of sophisticated gas and vapor detection solutions for the military, 1st responder, safety and homeland security markets. He has been a featured speaker at more than 20 international conferences including the American Chemical Society’s annual conference, NATO’s advanced research workshop and Jane’s Defense Weekly WMD conference.
Comments & Ratings

Issue 32.4 | Fall 2018

Past Issue Archives