OPTIMIZING THE PERFORMANCE OF AUTOMATED MONITORING SYSTEMS FOR AIRBORNE TOXIC CHEMICALS. Dr. Gary D. Sides August 5, 2014

Transcription

1 OPTIMIZING THE PERFORMANCE OF AUTOMATED MONITORING SYSTEMS FOR AIRBORNE TOXIC CHEMICALS Dr. Gary D. Sides August 5,

2 Topics Introduction Evolution of automated air monitoring systems for chemical agents Derivatization methods successfully employed Improved understanding of a mature detector 2

3 U.S. Stockpile of Chemical Weapons In 1994, the US stockpile of chemical weapons was formally declared in response to the U.S. signing the Chemical Weapons Convention in The US stockpile consisted of a total of 31,000 tons of sarin (GB), mustard (HD), and agent VX and small quantities of Lewisite (L) and tabun (GA). As of 2014, only about 3,135 tons of the US stockpile remains to be destroyed: 2,611 tons of HD at Pueblo Chemical Depot 306 tons of GB, 127 tons of VX, and 91 tons of HD at Bluegrass Army Depot 3

4 Examples of activities at disposal sites requiring the protection of workers, the general public, and the environment 4

5 Primary Roles of Chemical Agent Monitoring* To detect chemical agent and sound an alarm if concentrations greater than the applicable airborne exposure limit are reported as the result of the failure of a system, operation, or process To provide an early warning of a problem that may result in the detection of agent outside engineering controls before the applicable airborne exposure limit is exceeded (by the use of monitoring trends) To ensure the use of appropriate PPE (personal protective equipment) for the area in which workers will be located (based on monitoring conducted prior to entry) *Also ensures that site personnel will be able to take appropriate actions immediately, in the event of the detection of agent to ensure the protection of workers, the general public, and the environment. 5

6 Airborne Exposure Limits (AELs) mg/m 3 GPL WPL STEL SEL IDLH GB VX HD GB (Sarin) VX HD (Mustard) 6

7 Airborne Exposure Limits (AELs) parts per trillion by volume* GPL WPL STEL** SEL IDLH GB VX HD , ,000 *To meet quality requirements, air monitoring methods must be capable of monitoring concentrations as low as 0.2 AEL. **Also, known as the Vapor Screening Limit (VSL), when used to clear decontaminated items. 7

8 8 AUTOMATED AIR MONITORING SYSTEMS

9 Automatic Continuous Air Monitoring System (ACAMS) Automated monitoring system based on: Collection of the chemical agent of interest using an internal solid-sorbent tube Courtesy of Meadoworks, Inc., Rupert, West Virginia Separation of the agent from other chemicals using, capillary gas chromatography Detection using a flame photometric detector (FPD) ß time The ACAMS reports the chemical agent concentration once every 5 min. 9

10 ACAMS a well proven, mature technology First developed for use at the CAMDS disposal site, Deseret Chemical Depot (DCD), in 1980 Used at the JACADS chemical agent disposal site, Johnston Atoll, Used at other agent disposal sites (ANCDF, PBCDF, TOCDF, and UMCDF),

11 Previous Generations Automatic Continuous Air Monitoring System (ACAMS) Developed by Dr. Sides at Southern Research Institute ( ) Used at five incinerator-based agent disposal sites (CMA) 65 pounds, 1.7 cu. ft., twelve (12) circuit boards, complex wiring Complex GC-based sampling and analytical system Miniature Automatic Continuous Air Monitoring System (MINICAMS ) Developed by Dr. Sides, founder of CMS Research Corporation ( ) Used at four alternative technologies agent disposal sites (ACWA) 18 pounds, 0.9 cu. ft., six (6) through-hole circuit boards, complex wiring Moderately complex GC-based sampling and analytical system MINICAMS is a registered trademark of CMS Research Corporation, Pelham, Alabama 11

12 Air Alert A third generation air monitoring system from Gary Sides Flexible sampling and analytical platform with space for expansion Sampling and analytical components plug-in for ease of replacement Readily reconfigured for various applications (removable module) Only two surface-mount circuit boards Only six simple wiring harnesses Lower cost of manufacturing Reduced weight (13 pounds) 0.7 cubic feet 12

13 Air Alert with an FPD Sampling and analytical module with a flame photometric detector (FPD) Detection of sulfur- and phosphorus-containing organic chemicals 13

14 Air Alert with a CSD Sampling and analytical module with a chlorine selective detector (CSD) Detection of chlorine-containing organic chemicals 14

15 Air Alert Data Acquisition System 15

16 16 DERIVATIZATION AND THE DETECTION OF AIRBORNE AGENT VX

17 Determination of Agent VX O H 3 C - P - S - CH 2CH 2 - N OCH 2CH 3 CH(CH 3) CH(CH 3) 15-min STEL concentration is less than one part per trillion VX vapor pressure is about mmhg at 20 C VX is a polar molecule and difficult to transport through sample tubing O H 3 C - P - S - CH 2CH 2 - N CH(CH 3) 2 O + AgF H 3 C - P - F + Ag - S - CH 2 CH 2 - N CH(CH 3) 2 OCH 2CH 3 CH(CH 3) 2 OCH 2 CH 3 CH(CH 3) 2 B. Saville, The Concerted Action of Fluoride and Silver Ions on Diethyl Ethylphosphonothiolate in Aqueous Solution, J. Chem. Soc., 1961,

18 Determination of Agent VX O H 3 C - P - S - CH 2CH 2 - N CH(CH 3) 2 O + AgF H 3 C - P - F + Ag - S - CH 2 CH 2 - N CH(CH 3) 2 OCH 2CH 3 CH(CH 3) 2 OCH 2 CH 3 VX G-analog of VX CH(CH 3) 2 18

19 Determination of GA (Tabun) O O N P O CN AgNO 3 KF N P O F + AgCN GA Fluorotabun (FT) GB GA VX 19

20 20 DERIVATIZATION, A DETECTOR CHANGE, AND AIRBORNE LEWISITE I

21 Goal of the Initial Development of a Lewisite Monitoring System at CMS Research in the Mid 1990s Develop the ability to monitor for Lewisite 1 at its 15-min STEL concentration (0.003 mg/m 3 or 3 ng/l) using a modified MINICAMS. Cl As Cl Cl Volatility (mg/m 3 ): Lewisite 1 20 C Mustard (HD) 20 C Challenges: Reactive (hydrolysis) and thermally labile, Lewisite 1 cannot be thermally desorbed from a porous polymer sorbent bed Thermally labile, Lewisite 1 is difficult to determine by GC MINICAMS in early 1990s was configured only with a flame photometric detector (S or P) 21

22 Lewisite 1 Normally Derivatized Prior to Determination by Gas Chromatography Reaction with British Anti-Lewisite (2,3-dimercapto-1-propanol) Cl As Cl Cl + HS HS OH Cl As S S OH + 2 HCl Reaction with 1,2-ethanedithiol (EDT) in solution to form LD Cl As Cl Cl + HS HS Cl As S S + 2 HCl Challenge: Near-real-time derivatization (gas phase or on a substrate) 22

23 Typical FPD-MINICAMS Chromatogram for a Lewisite Challenge (with EDT in gas phase) Cl As S S Chromatogram courtesy of Sandra Macon, CMS Field Products (OICO) 23

24 FPD-MINICAMS Chromatogram for a Lewisite Challenge (with a higher EDT concentration) Cl As S S Chromatogram courtesy of Sandra Macon, CMS Field Products (OICO) 24

25 OICO s Halogen Selective Detector (XSD), Developed in 1995, Adapted to MINICAMS Cl As S S Selective for chlorine MDL < 0.1 ng chlorine Supplied EDT (200 ppmv in nitrogen) from a compressed gas cylinder 25

26 Chromatogram for a Lewisite Challenge Obtained Using an XSD-MINICAMS Cl As S S 26 Chromatogram courtesy of Sandra Macon, CMS Field Products (OICO)

27 27 IMPROVED UNDERSTANDING OF A MATURE DETECTOR

28 Halogen Selective Detector (XSD) Response assumed linear for the concentration ranges of interest Data quality objectives (DQOs) passed but with some issues DQOs could not be met reliably when concentration range of interest was increased 28

29 OICO Applications Note for the XSD Response linear and through origin (0,0) only at low masses Response non-linear at higher masses OICO Applications Note , entitled Using the Halogen Specific Detector (XSD TM ) as an Alternative to the ELCD in USEPA Methods 29

30 OICO Notes on Operation of the XSD September 2, 1994 Dr. Rich Simon, Developer of the XSD at OICO Langmuir adsorption model H = α (VSL) 1 + β (VSL) where α and β are constants and H is the peak height *For a sample flow rate of 450 ml/min and sample period of 3 min 30

31 Dale Coulson s Patent

32 SRI Instruments (Las Vegas, Nevada) Licensed Dale Coulson s Detector Sold as the Dry Electrolytic Conductivity Detector (DELCD) Response linear and through origin (0,0) only at low masses Response non-linear at higher masses Data from Xiaojing Li (2009) Data from Xiaojing Li (2009) 32

33 Accounting for Non-Linearity of the XSD Langmuir response can be approximated over the concentration range of interest using a standard feature of the MINICAMS software Concn = (Peak Height/CAL Height) 1/n Data quality objectives were then easily met 33

34 To Optimize Instrument Performance Constant development and improvement in hardware and embedded code required Willingness to consider derivatization methods important Willingness to question current practices (assumptions) important 34