Decision-making in CWA response

CarolinaFireJournal - Chris Wrenn
Chris Wrenn
04/26/2010 -

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

In responses to release 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.


CWA Identification

After a chemical has been located and classified in some special situations it is necessary to identify it. Speciation (typically spectroscopy) technologies allow us to identify chemicals so that additional actions can be taken. “Spectroscopy” is the study of how electromagnetic radiation interacts with the atoms and molecules:



  • “Infrared” or FTIR spectroscopy is the study of how infrared light is absorbed by the bonds between atoms that form molecules

  • “Raman” spectroscopy is the study of how laser light interacts with the bonds between atoms that form molecules

  • Mass Spectroscopy ionizes pure chemical peaks, produced by a gas chromatograph, which breaks down into characteristic and identifiable pieces; this spectral “fingerprint” is unique to a particular chemical and can be matched to a library.

    Essentially spectroscopy is the science of taking a “picture” and matching that picture to another known “picture” in a library. Once a spectra is acquired the system software can perform a search analysis for the “unknown” in question.

FTIR Spectroscopy

In Fourier Transform Infrared (FTIR) spectroscopy, infrared (IR) radiation is passed through a sample. Wavelengths of IR light that a chemical absorbs determines what that chemical is — fingerprint. Each molecular structure has a unique combination of atoms and produces a unique infrared spectrum — identification = qualitative.

When FTIR is used for gas/vapor measurement, thanks to the Beer-Lambert Law the amount of IR that is absorbed (intensity) determines how much chemical is there — concentration = quantitative.

FTIR is a proven technology for chemical identification used for over 50 years in applications from laboratories to law enforcement and industry.

FTIR can be used to identify some solids, pastes and liquids including CWAs. FTIR can also be used to identify some gases and vapors including CWAs. FTIR analyzers are typically fast acting and easy to use. Their ability to handle mixtures varies with vendor, although some products will not be able to see a component in a mixture if it accounts for 10 percent or less of the mixture. They typically have the advantage of low lifetime costs but they can be expensive — $10’s of thousands to purchase. 


  • Can identify many solids, liquids, pastes, gases & vapors

  • Relatively easy to use

  • Low calibration and logistical requirements

  • Stores well


  • Either solids or gases not both

  • Some difficulty with mixtures

  • Some are heavy and bulky

  • Very expensive to purchase

Raman Spectroscopy

In Raman Spectroscopy a laser light source is beamed into a substance. The laser light photons excite the electrons in the sample substance and the electrons reemit photons as they return to their base state. The frequency of the reemitted photons is shifted up or down in comparison with the original laser light and this compound specific characteristic is called the Raman Effect. It is named for one of its discoverers Sir C.V. Raman who won the Nobel Peace Prize in physics for the discovery in 1930.

Raman can be used to identify some solids, pastes and liquids including CWAs. Raman cannot, measure gases and vapors. However, while Raman cannot detect gases and vapors it is included because due to the low vapor pressure of CWAs, there may be liquid samples present for analysis. Some Raman products have the same issue with mixtures as FTIR and may not be able to see a component if it makes up 10 percent or less of the mixture.


  • Can identify many solids, liquids, pastes without sample handling or preparation

  • Raman can penetrate many containers

  • Relatively easy to use

  • Stores well

  • Low calibration and logistical requirements


  • Cannot do gases or vapors

  • Very expensive — around $30K — to purchase

Gas Chromatography/Mass Spectroscopy

GC/MS is the combination of two technologies to help identify gases or vapors:

Gas Chromatography (GC): separates high boiling from low boiling chemicals — low vapor pressure from high vapor pressure — and puts them into “peaks” that represent their characteristic travel time through a chromatography column — a small very small capillary tube. High boiling — low vapor pressure — compounds have longer retention time in the capillary than low boiling — high vapor pressure — compounds. The resulting graph is called a “chromatogram” which shows a series of peaks representing different chemicals separated by the time that each takes through the column. 

Mass Spectroscopy (MS): ionizes these pure chemical peaks which break down into characteristic and identifiable pieces. This spectral “fingerprint” is unique to a particular chemical and can be matched to a spectral library. In the Ionizer a corona discharge ionizes the peaks into ions. In the Quadrupole Rods the ions are electronically filtered and separated before they reach the detector, which measures their response. 

Some portable GC/MS have a survey mode in addition to the GC/MS mode. In this survey mode the GC is by-passed and the sample is drawn directly into the MS. This gives quicker response time of about two minutes versus the 15-25 minute process time for GC/MS mode. Survey mode can analyze relatively pure samples to 10’s of ppm but had difficulty with mixtures and providing low levels of sensitivity.

In GC/MS mode the GC separates each chemical into peaks and then each peak is further separated into ions for identification by the MS. This mode is most useful for separating mixtures and has high sensitivity (10’s of ppb) but it takes much longer, 15-25 minutes per sample. 


  • The “Gold Standard” of gas detection

  • Very accurate

  • Very specific


  •  Very expensive to purchase ($60-$100K)

  • “Snap Shots,” non-continuous (MS can run continuous)

  • Respond in minutes rather than seconds (~2 min in survey ~20 min in GC/MS mode)

  • Very complicated & training intensive

  • Very heavy and bulky

  • Doesn’t store well (NEG vacuum pumps prefer constant rather than intermittent use)

  • ~$35/hr to use

Life Cycle Costs and Sustainability

When purchasing expensive detection technologies for CWA response one should consider not only the cost of acquisition, but also the cost of ownership. Some products need expensive consumables or services which can mean very expensive hourly run-rate costs. Some products have unusual logistics demands — like requiring unusual gases to operate — that may not be readily available during a national emergency. Some products may not store well — requiring weekly/monthly “exercising.” Some may need a long time to “warm up” — as long as an hour or two — after extended periods of storage. When looking to purchase, make sure you know the entire story or you could be surprised!

In addition to purchase cost, look for products that have low cost of ownership — if all else is equal. Look for products that have multiple uses. This allows operators to become familiar with their performance across a wide range of applications. Single use products like CWA only detection technologies tend to get underutilized and users quickly use their aptitude when they are not frequently using a detection technology.

Integrating Our Gas Detection Technologies

Every technology has its strengths and weakness.  In the following chart there are three continuums. The top line moves from broadband detection to very specific gaseous detection. The second line is a metaphoric line and the lowest line represents speed of detection. A PID can locate contamination in seconds. Metaphorically speaking the PID can get to the right state in seconds. An IMS product can classify in 10’s of seconds. Metaphorically speaking it can get to the right town in 20-30 seconds. A GC/MS can identify a gas/vapor in 15-25 minutes. Metaphorically speaking it can identify the correct “address” in 15-25 minutes. So a PID can be used to find contamination while an IMS can classify it.  While classification is adequate for making antidote decisions in the field it isn’t good enough for evidence and a GC/MS, Raman or FTIR analysis of the sample provides more solid identification.

Putting It All Together

In the circle diagram, each circle represents whether or not a particular technique/clue is providing a positive response. By overlaying multiple techniques we can zoom in on the solution just like a detective uses multiple clues to solve a crime. Use multiple techniques until you feel comfortable with the solution.


Physical Clues

  • Any signs of dissemination techniques?

  • What is going on with the weather or indoor environment?

  • Are there any physical clues?

Biological clues

  • Are there any dead animals or ones that display SLUDGEM/DUMBBELLS type symptoms?

  • Are there any human victims displaying SLUDGEM/DUMBBELLS symptoms?

Location devices

  • Using PID, FID, M9 are there any areas of higher concentrations?

Classification devices

  • What are the color change technologies telling you?

  • What is your CWA detection technology(s) telling you?

Identification devices

  • Verify the above clues with an identification technology

In the future represented by the old TV show Star Trek, one of the characters, Mr. Spock, used a “tricorder” to analyze unknown environments. But even in this future the tricorder was given to the smartest guy on the spaceship. In present day CWA response we must be smart in coming to decisions using not only the high-tech detection technologies that we are provided with, but also the clues that we can see with our own eyes.

Christopher Wrenn is the Sr. Director of Sales and Marketing for Environics. He has written numerous articles, papers and book chapters on gas detection in HazMat and industrial safety applications.
Comments & Ratings

  5/24/2013 12:42:01 AM

New Comment 
Hello Anupbhai!A really great locigal article. I would like to ask you following: I am an Engineer (B.E. civil engineering) with M.Tech. in Project Management and presently working in an EPC firm as a Project Planning & Scheduling Manager. I have about 6 years of experience in the same field. I am 31 years. I wanted to add some professional certifications further and shortlisted some courses like PMP (Project management professional), CWA etc. I was impressed with the kind of syllabus ICWAI was having. My question is: 1. Do you feel that having CWA qualifications will help me rapidly grow in my career of Project Management (may be very senior position in large EPC firm like L&T/Siemens or something like that) 2. Whether with CWA certification, can i go in to field of Infrastructure financing (which i have natural inclination a bit) in the firm like IL&FS/IDFC. What are the chances of going in these kind of field? 3. Overall, do u feel that CWA will be very different qualifications to mykind of profile and i should look forward to another qualifications/certifications OR do u feel it will be most complementary certification to my kind of profile??Awaiting your reply before i take my final call.RegardsAwaiting your frank and neutral reply.

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