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Soldier Protective Clothing and Equipment: Feasibility of Chemical Testing Using a Fully Articulated Robotic Mannequin
3
Design Challenge: Mannequin Under-Ensemble Sensing
This chapter mainly discusses the following two PETMAN design challenges:
3.2.4 The study will determine the feasibility of designing a PETMAN system with an integrated under-ensemble sampling system that will allow for the collection of agent breakthrough data in real time (1-second increments).
3.2.6 The study will determine the feasibility of designing a PETMAN system capable of operating in fixed environmental chamber conditions (T) and a range of environmental chamber conditions (O) as defined in 3.3.6.1-3.3.6.5.
The design, fit, or size of the protective garment will influence chemical-agent penetration. When worn, clothing is subjected to pressure differentials across the garment due to breathing, wind, or the bellows effect created by body movement, which may force chemical-warfare agent (CWA) or toxic industrial chemicals (TICs) vapor or aerosol through the clothing fabric and closures. Bending and moving stresses clothing, particularly over the joints. To determine penetration of chemical-protective ensembles by chemical vapor or aerosol, it is necessary to test the entire suit system, including seams, closures, and areas of transition with other protective equipment, that is, at the ankles, waist, wrists, and neck. In addition, aspects of the PETMAN tests such as the environmental conditions of the test chamber will also impact CWA penetration through the soldier IPE.
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Soldier Protective Clothing and Equipment: Feasibility of Chemical Testing Using a Fully Articulated Robotic Mannequin
In addition to the two design challenges given above, consideration will also be given to the PETMAN design challenge concerning mannequin support, which also impacts the feasibility of CWA sampling technologies:
3.2.1 The study will determine the feasibility of designing a PETMAN system to be tethered (T) or free standing/self-contained (O). A tethered PETMAN system design must not compromise the integrity of the individual protection ensemble equipment being tested on the PETMAN system. If a tethered design is selected the design must also minimize the impact to the whole ensemble operation.
RELEVANT PETMAN REQUIREMENTS
The relevant PETMAN requirements (Box 3.1) and various technologies for the detection of CWAs for potential use in the PETMAN mannequin are discussed below.
Other Considerations
Some conditions in addition to the PETMAN system design challenges and requirements designated above should also apply to ensure proper functioning of the sensor technology in the context of all other PETMAN requirements.
The technology should be:
Unaffected by perspiration (water vapor) beneath the garment ensemble
Unaffected by any potential interferents from garment material or residual decontamination cleanser and chemicals off-gassing
Packaged in a durable device that can withstand rough handling and repeated use
Portable enough to be conveniently placed in different locations on the test mannequin and beneath the protective garment
Unaffected by “false-positive” readings (for example, readings that result from residual volatile additives in the protective-garment material, decontamination chemicals and cleansers, or from moisture interference)
Currently available in a usable product form
Have minimal impact on internal airflow within the suit
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BOX 3.1
Relevant PETMAN Requirements
3.3.2 The PETMAN system shall be capable of operation for twelve (12) hours prior to requiring operational maintenance, three (3) months prior to preventive maintenance and six (6) months prior to calibration. (T) The PETMAN system shall be capable of operation for twenty-four (24) hours prior to requiring operational maintenance, six (6) months prior to preventive maintenance and twelve (12) months prior to calibration. (O) Operational maintenance is defined as the required maintenance procedures to prepare the PETMAN system for each test trial, for example, filling a perspiration reservoir, changing agent samplers or decontamination before the next trial. Preventive maintenance is defined as a maintenance event performed prior to a failure in order to prevent its occurrence.
3.3.5 The PETMAN system shall be compatible with current under ensemble chemical breakthrough sampling technologies, procedures, and equipment as defined in Test Operations Procedure (TOP) 10-2-022, Chemical Vapor and Aerosol System-Level Testing of Chemical/Biological Protective Suits (T) and designed to enable integration with real-time (1-second increments) sampling technologies, procedures, and equipment (O). At a minimum, sampling locations shall be the same as those defined in TOP 10-2-022 (see Figure 3.1 and Table 3.1).
3.3.6 The PETMAN system operation shall not be affected by the following chamber environmental conditions.
3.3.6.1 Temperature: 90°F ± 2°F (T); −25°F to 125°F ± 1°F, measured every 5 minutes (O)
3.3.6.2 Relative Humidity: 80% ± 3% (T); 0-100% ± 1%, measured every 5 minutes (O)
3.3.6.3 Wind speed: 0-10 mph ± 10% (T); 0-161 mph ± 2 mph (O)
3.3.6.4 Pressure: 0.25 iwg chamber vacuum maintained ± 2%
3.3.6.5 Liquid and vapor chemical agents including all nerve and vesicant agents, as well as the chemical simulants, triethylphosphate and methyl salicylate.
3.3.12 The PETMAN system shall utilize as many common commercially available parts and/or components as possible.
3.3.13 The PETMAN system shall record the following system parameters over time: skin temperature, respiration rate, perspiration rate, and total mass (in nanograms) of chemical vapor that penetrates/permeates through the protective ensemble. The PETMAN system shall record the start and stop time of each motion in 1 second increments.
NOTE: T=threshold and O=objective
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FIGURE 3.1 Sampling locations for the Passive Absorbent Devices (PADs) for Man-in-Simulant Test (MIST); Chemical Vapor and Aerosol System-Level testing of chemical/biological protective suits.
SOURCE: U.S. Army Developmental Test Command Test Operations Procedure (TOP) 10-2-022. December 14, 2005. Chemical Vapor and Aerosol System-Level Testing of Chemical/Biological Protective Suits. DTIC AD No. ADA440290.
CURRENT DETECTION TECHNOLOGIES
A chemical sensor uses chemical (and possibly biologic) reactions to detect and quantify a specific analyte. Such devices are usually self-contained and have a sorptive surface that interacts chemically with the analyte of interest (commonly a polymeric membrane or coating that contains a specific low-molecular-weight “doping agent”), a transducer that detects the chemical event occurring between the surface and the analyte, and supporting electronics or software that amplifies and reports the output signal
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TABLE 3.1 Passive Absorptive Device (PAD) Placement Location Descriptions; Individual Protective Equipment for Selectively Permeable Membrane Materials Man-in-Simulant Test, as Shown in Figure 3.1
Position Numbera
Description
P21
Scalp
P22
Left Ear
P24
Chin
P25, PD25b
Nape
P26
Armpit
P27
Inner Upper Arm
P28
Outer Upper Arm
P29
Forearm, Volar
P30
Mid Back
P31
Abdomen
P32, PD32b
Buttocks
P33, PD33b
Groin
P34
Crotch/Scrotum
P35
Inner Thigh
P36, PD36b
Inner Shin
P37
Blank Transport Sample for Quality Control (QC)
P38
Spike Transport Sample for QC
Don
Dress Area
Doff
Undress Area
P90
Nose Cup
P91c
Mask
P92
Glove (Hand)
P93
Boot (Foot)
aSee Figure 3.1.
bIndicates duplicate PSD at these locations.
cPSD placed in transport case to monitor cross-contamination.
SOURCE: U.S. Army Developmental Test Command Test Operations Procedure (TOP) 10-2-022. 14 December 2005. Chemical Vapor and Aerosol System-Level Testing of Chemical/ Biological Protective Suits. DTIC AD No. ADA440290.
from the transducer. The sorptive material is probably the most critical component of the sensor in terms of determining the sensitivity and selectivity, regardless of the transducer.1
1
Grate, J. W., and D. A. Nelson. 2003. Sorptive Polymeric Materials and Photopatterned Films for Gas Phase Chemical Microsensors. Proceedings of the IEEE 91(6):881-889.
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TABLE 3.2 Overview of Technologies Currently Available for Detection of CWAs, TICs, and TIMs
Technology
Principle
Chemicapacitor technology
An array of polymer-filled chemically sensitive capacitors, detects the presence of vapors in the air. A single 2 × 5-mm chip has the potential to contain an array of up to eight capacitors. A more detailed discussion is presented below.
Electrochemical sensors
These sensors operate by reacting with the gas or vapor of interest and producing an electric signal that is proportional to the gas or vapor concentration.
Fiber-optics-based sensor
A polymer-, porphyrin-, or enzyme-treated substrate is subjected to a specified range of light. The response of the detection system to the nonabsorbed radiation determines the types and amounts of chemical agents present. A more detailed discussion is presented below.
Flame-ionization detector (FID)
A FID is an ion detector that uses an air-hydrogen flame to produce ions. As components elute from the gas chromatograph’s column, they pass through the flame and are burned, producing ions. The ions produce an electric current, which is the signal output of the detector. The greater the concentration of the component, the more ions are produced and the greater the current.
Many technologies exist for detecting CWAs, TICs and TIMs, and have been reviewed extensively elsewhere.2 A list of some potential detection technologies for PETMAN is given in Table 3.2 and evaluated in Table 3.3. Three of these detection transducers at various stages of
2
See the following reviews and others for more information on chemical and biological sensing technologies: Dadik, O., W. H. Land, Jr., and J. Wang. 2003. Targeting Chemical and Biological Warfare Agents at the Molecular Level. Electroanalysis 15(14):1149-1159; Seto, Y., M. Kanamori-Kataoka, K. Tsuge, I. Ohsawa, K. Matsushita, H. Sekiguchi, T. Itoi, K., Y. Sano, and S. Yamashiro. 2005. Sensing Technology for Chemical-Warfare Agents and Its Evaluation Using Authentic Agents. Sensors and Actuators, B: Chemical 108:193-197; Sun, Y., and K. Y. Ong. Detection Technologies for Chemical Warfare Agents and Toxic Vapors, CRC Press (2004).
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Technology
Principle
Ion-mobility spectrometer (IMS)
A radioactive source is used to ionize the target gas; the resulting ions are directed into a drift chamber where they are separated by mass and charge. The amount of ions of each mass or charge collected determines the amount and type of gas or vapor molecules present.
Passive adsorptive devices (PADs)
PADS technology uses packets of Tenax® that adsorb the agent simulant methyl salicylate. Afterward, the simulant is desorbed from the Tenax and quantified. This technique is currently used in the Man-in-Siumulant-Test.
Photoionization detector (PID)
A PID uses an ion detector having high-energy photons, typically in the UV range, to produce ions. As components elute from the gas-chromatograph column, they are bombarded by high-energy photons and are ionized. The ions produce an electric current, which is the signal output of the detector. The greater the concentration of the component, the more ions are produced and the greater the current.
Surface acoustic wave (SAW)
Detection is based on the change in the propagation of an acoustic wave over a piezoelectric substrate treated with a polymeric coating. A more detailed discussion is presented below.
development—chemicapacitor, fiber-optics, and surface acoustical wave (SAW)—were chosen as illustrative examples for evaluating the feasibility of the PETMAN requirements in more detail. The chemicapacitor technology is commercially available but not widely used, fiber-optics based is not commercially available but has the potential to be developed with the next year, and SAW based is commercially available and widely used in many application areas. In Tables 3.4 through 3.6 the three technologies and the current passive absorptive devices (PADs) currently used in the MIST are compared based on how they all address the PETMAN requirements.
Chemicapacitor Detection Technology
Chemicapacitor sensors measure the change in dielectric constant of selectively adsorbing materials such as a polymer or single-walled carbon
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TABLE 3.3 Ratings of Detection Technology for Various Characteristics (L = little or no capability, M = medium capability, H = highest capability or most desirable)
Chemicapacitor
Electrochemical
Fiber-Optics
FID
IMS
PADs
PID
SAW
Range of CWAs detected
H
L
H
L
H
Unknown
M
H
Range of TICs detected
L
M
H
L
M
Unknown
M
L
Selectivity for agents detected
H
M
H
L
L
Unknown
L
H
Sensitivity to CWAs
H
L
M-H (depends on system)
L
H
Unknown
L
H
Relative size or footprint (smaller is more desirable)
M
L
H
L
L
H
L
M
Start-up time (shortest time is most desirable)
H
M
H
M
M
H
M
M
Response time (≤ 1 s is most desirable)
M
M
H
M
M
L
M
M
Potential for wireless power source
Yes
Yes
Yes
Yes
Yes
Not powered
Yes
Yes
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TABLE 3.4 Comparison of Various Detection Technologies with PADs in Meeting Threshold PETMAN Program Requirements
Requirement
Chemicapacitor
Fiber Optics
PADs
SAW
Commercialized
Yes
No
No
Yes
Can be placed at all sampling locations defined in TOP 10-2-022 (see Section 3.3.5)
Yes
Yes
Yes
Yes
Capable of detecting specified agents—nerve agent GB and vesicant HD—and their simulants, triethyl phosphate and methyl salicylate, respectively (see Section 3.3.6)
Yesa
Yes
Yes
Yes
Capable of detecting nanogram levels of agent or simulant penetration or permeation
Yes
Yes
Not applicable
Yes
Capable of operating for 12 hours before requiring operational maintenance, three months before preventive maintenance, and six months before to calibration (see Section 3.3.2)
Yesb
Yes
Not applicable
Yes
Compatible with current under-ensemble chemical-breakthrough sampling technologies, procedures, and equipment as defined in TOP 10-2-022 (see Section 3.3.5)
Yes
Yes
Yes
Yes
Operational at (not affected by) a temperature of 90 ± 2°F (see Section 3.3.6.1)
Yes
Yes
Yes
Yes
aLimits of detection have to be determined or confirmed.
bLong-term testing has yet to be performed.
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TABLE 3.5 Comparison of Various Detection Technologies to Meet Objective PETMAN Program Requirements
Requirement
Chemicapacitor
Fiber Optics
PADs
SAW
Powered in such a manner that it does not require tethering to a power source, for example, battery-powered and wireless (see Section 3.2.1)
Yes
Yes
Yes
Yes
Capable of operating for 24 h before requiring operational maintenance, 6 months before preventive maintenance, and 12 months before calibration (see Section 3.3.2)
Yesa
Yes
Not applicable
Yes
Able to detect and report agent or simulant permeation or penetration in real time in 1 second increments (see Section 3.3.5)
Yes
Yes
No
No
Operational at (not affected by) temperatures of −25 to 125 ± 1°F (see Section 3.3.6.1); note, however, that if a mannequin skin that evolves metabolic heat is developed, a temperature of −25°F may not be reached
Unknown (known to operate at 32-125°F)
Unknown
Unknown
Unknown (known to operate at 14-104°F)
aLong-term testing has yet to be performed.
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TABLE 3.6 Comparison of Various Detection Technologies to Address “Other Considerations” for the PETMAN Program
Consideration
Chemicapacitor
Fiber Optics
PADs
SAW
Immune to potential effects of perspiration or water vapor beneath garment ensemble to be tested
Yes
Likelya
Yes
Yes
Immune to potential interferents from off-gassing from polymers (from which garments may be made), decontamination chemicals, and cleansers
Yes
Likelya
Possibly no
Yes
Packaged in durable device that can withstand rough handling and repeated use
Yes
Yes
Yes
Yes
Portable enough to be conveniently placed in different location on test mannequin and beneath garment?
Yes
Yes
Yes
Yesb
Results in “false-positive” reading for test agents (GB, HD, or simulants)
Noc
Noc
Unknown
No
aAdditional testing must be performed to confirm that sensor is not affected by perspiration or water vapor or by components that may off-gas from protective garment.
bAdditional development work will be necessary to reduce “footprint” and profile of device.
cAdditional testing must be performed to confirm that no “false-positive” readings occur.
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nanotube,3 and are capable of detecting organic vapors, 4 and inorganic gases—including CWAs and TICS.5 Early sensors measured capacitive humidity.6 Current commercially available chemicapacitor sensor arrays contain 8 to 16 sensors on a 2 × 5-mm chip, which allows for a small, portable detector package (with electronics measuring about 2.5 × 2 × 1 in.).7 Key characteristics of chemicapacitor sensing based on the references cited are given below.
Dynamic Range and Detection Limit: Sensitivity to most VOCs is in the low parts per million (ppm) range. Limits vary with the vapor pressure of the target analyte.
Response Time: The mass-transfer limitations of the thick chemoselective dielectric material (~1 μm) may cause a sensor to appear slower than it is. Under optimal conditions in the laboratory, the chemicapacitors demonstrate a response time of less than 1 s and a recovery time of 1-2 s after exposure to many vapors.
Response over Temperatures and Humidities: Chemicapacitor sensors have been tested over a temperature range of 32-125°F and over the full range of relative humidity (0-100% noncondensing). As in all polymer-based technologies, sensitivity is a function of the temperature and vapor pressure of the target.
Fiber-Optics-Based Detection Technology
Fiber-optics-based chemical agent detection uses optical spectroscopy to detect chemicals absorbed to an active polymer-, porphyrin-, or enzyme-treated substrate.8 Optical signals pass to a detector by way of
3
Snow, E. S., F. K. Perkins, E. J. Houser, S. C. Badescu, and T. L. Reinecke. 2005. Chemical Detection with a Single-Walled Carbon Nanotube Capacitor. Science 307(5717):1942-1945.
4
Patel, S. V., T. E. Mlsna, B. Fruhberger, E. Klaassen, A. Cemalovic, and D. R. Baselt. 2003. Chemicapacitive Microsensors for Volatile Organic Compound Detection. Sensors and Actuators, B: Chemical 96(3):541-553.
5
Mlsna, T. E., S. Cemalovic, M. Warburton, S. T. Hobson, D. A. Mlsna, and S. V. Patel. 2006. Chemicapacitive Microsensors for Chemical Warfare Agent and Toxic Industrial Chemical Detection. Sensors and Actuators, B: Chemical 116(1-2):192-201.
6
Delapierre, G., H. Grange, B. Chambaz, and L. Destannes. 1983. Polymer-Based Capacitive Humidity Sensor: Characteristics and Experimental Results. Sensors and Actuators 4:97-104.
7
Seacoast Science, Inc.: http://www.seacoastscience.com/Downloads/Seacoast_White_Paper_DEC%202006.pdf, accessed August 28, 2007.
8
Wolfbeis, O. S. 2004. Fiber-Optic Chemical Sensors and Biosensors. Analytical Chemistry. 76(12):3269-3283.
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a single or bundle of optic fibers. The response of the detection system to the nonabsorbed radiation determines the types and amounts of chemical agents present. A key flexibility in the use of optical systems is the ability to incorporate optical fibers into the sensor system and allow one or more central sensor systems with fibers running to multiple locations in the mannequin.
These systems are used in variety of ways. The committee heard talks about two different fiber-optics-based chemical agent sensing approaches (see Appendix D). One way is with multiple chemical coatings (sensors) on bundled fibers that have differential partitioning of the target analyte.9 Another way uses a single fiber interacting with a solid-state substrate.10 Bundled fiber sensors can be constructed with thousands of fibers allowing the use of hundreds of coating replicates, which improve signal-to-noise ratios. In addition, a single coating can be placed over all the fibers in a bundle to improve sensitivity and reaction time. Key characteristics of fiber-optic sensing based on the references cited are given below.
Dynamic Range and Detection Limit: Some fiber-optics-based technologies can measure from 25 ng to over 1 μg of gas, but this can vary with the fiber-optics system.
Response Time: Under optimal conditions in the laboratory, the fiber-optics-based system has a response time of less than 1 s.
False-Positive Readings: Preliminary laboratory testing suggests the absence of false-positive readings. Additional laboratory testing is needed.
Response over Temperatures and Humidities: Preliminary laboratory testing suggests that fiber-optics-based systems can operate over a range of temperatures and humidities. Additional laboratory testing is needed.
9
Albert, K. J., and D. R. Walt. 2003. Information Coding in Artificial Olfaction Multisensor Arrays. Analytical Chemistry 75(16):4161-4167; Epstein, J. R., M. Lee, and D. R. Walt. 2002. High-Density Fiber-Optic Genosensor Microsphere Array Capable of Zeptomole Detection Limits. Analytical Chemistry 74(8):1836-1840; Walt, D. R. 2000. Molecular Biology: Bead-based Fiber-Optic Arrays. Science 287(5452):451-452.
10
White, B. J., and H. J. Harmon. 2005. Enzyme-Based Detection of Sarin (GB) Using Planar Waveguide Absorbance Spectroscopy. Sensor Letters 3(1-4):36-41; White, B. J., J. A. Legako, and H. J. Harmon. 2003. Extended Lifetime of Reagentless Detector for Multiple Inhibitors of Acetylcholinesterase. Biosensors and Bioelectronics 18(5-6):729-734; Legako, J. A., B. J. White, and H. J. Harmon. 2003. Detection of Cyanide Using Immobilized Porphyrin and Myoglobin Surfaces. Sensors and Actuators, B: Chemical 91(1-3):128-132; White, B. J., J. A. Legako, and H .J. Harmon. 2003. Spectrophotometric Detection of Cholinesterase Inhibitors with an Integrated Acetyl-/Butyrylcholinesterase Surface Sensors and Actuators, B: Chemical 89(1-2):107-111.
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Surface Acoustic Wave (SAW) Sensors
SAW sensors are a mature technology first described in the 1970s.11 Many advances in this technology have been made since then.12 SAW chemical sensors are based on the change in the propagation of an acoustic wave over a piezoelectric substrate treated with a polymer coating. The polymer coatings or films are selected so that each will have a different chemical affinity for CWAs and TICs. In operation, SAW sensors are typically used in conjunction with a sample preconcentrator. Key characteristics of SAW technology based on the cited references are presented below.
Dynamic Range and Detection Limit: The dynamic range of a typical SAW chemical sensor is 5-6 orders of magnitude, measuring from about 1 pg to 1 μg of vapor. However, it depends on the vapor being measured. Nerve agents, such as GB, can usually be detected at less than 1 mg/m3, whereas the detection limit for HD is about 1-2 mg/m3.
Response Time: The time for the sensor to respond to mass changes in the selective polymer coating is usually less than 1 ms. In typical vapor-sensing applications, however, it is more likely that the response time will be determined by the time needed for the preconcentrator to obtain the sample, then for the vapor to be transported to the polymer-coating surface and for equilibrium to be established. The true response time could be greater than 10 s (with currently available systems).
False-Positive Readings: SAW devices are effective and reliable for detection of very small amounts of CWAs, such as GB and HD. SAW devices are typically not subject to false alarms due to the presence of other compounds in the sample stream. A preliminary separations stage and careful experimental procedure design should minimize the risk of false positives due to garment off-gassing or residual decontamination chemicals. If designed properly, a SAW detector can be used to detect CWAs effectively in a variety of environmental conditions.
Response Over Temperatures and Humidities: Although the polymer coatings used in SAW sensors can change physically when the devices are exposed to conditions outside the operating-temperature range, testing has
11
H. Wohltjen, and R. Dessy. 1979. Surface Acoustic Wave Probe for Chemical Analysis I. Introduction and Instrument Design. Analytical Chemistry 51(9):1458-1475.
12
See the following reviews for more information: Grate, J. W. 2000. Acoustic Wave Microsensor Arrays for Vapor Sensing. Chemical Reviews 10(7):2627-2648; Smith, J. P., and V. Hinson-Smith. 2006. Product Review: The New Era of SAW Devices. Analytical Chemistry, June 1, pp. 3505-3507.
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confirmed that SAW sensors can maintain their accuracy in temperatures of 14-104°F. The various polymer coatings used in the SAW devices have various sensitivities to humidity, so a concentrator can be incorporated into the design to permit moisture to bypass the detectors while vapors of interest are analyzed.
DESIGN CHALLENGES AND HOW THEY MAY BE ADDRESSED
Although the technologies cited above have the ability to detect CWAs, meeting most of or all the requirements cited in Tables 3.5 through 3.7, several design challenges are related to their adaptation or incorporation into the PETMAN system. Those challenges are categorized as associated with optimization or tailoring of the basic sensing technologies for this application or with incorporation into a mobile PETMAN mannequin. The challenges are discussed below.
Challenges Associated with Validation and Optimization for the PETMAN System
The sensor systems that need to be validated and optimized for use in the PETMAN system have several aspects, such as size, time response, “recovery time,” and hysteresis.
Size (“Footprint” and Profile): Obviously, some sensor technologies have a smaller footprint and profile than others. The “footprint” and thickness or volume should be minimized so that they do not interfere with the operation of the PETMAN or the “natural” movement of the garment. The PAD sampler is 1.5 × 1.25 × 1/8 inches. Current SAW devices are 3.5 × 2 × 1.2 inches and chemicapacitor devices are about 2.5 × 1.5 × 0.5 inches. However, the sensing component in these devices is only a fraction of the size, so it may be possible to separate the location where the analyte-coating interaction occurs (the sensor) from the electronics that power the unit to minimize the size of the devices. Fiber-optic sensors are likely to be much smaller and may be easier to incorporate into the PETMAN system.
Effects of Humidity: Testing is needed to ensure that the detector is not affected by condensed moisture (for example, associated with perspiration).
Time of Response: It is estimated that SAW sensors can make readings every 10 s or more. That meets the threshold requirement (T), but additional SAW sensor development may be required if the stated objective (O) of a reading every 1 s is to be achieved. The chemicapacitor and fiber-optics-based sensors are expected to have response times of 1 s or less. If a
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preconcentrator or an initial separation stage is required, this time required for analysis could increase.
Effects of Temperature: The SAW sensor will provide an accurate estimate of the amount of agent present over a temperature range of 14-104°F. Testing will have to be performed to determine the influence of temperature on the performance of the fiber-optics-based and chemicapacitor sensors. If the stated PETMAN objective requirement of 125°F is to be achieved, a major R&D effort for sensor-coatings could be necessary.
Reversible Response of Sensors: Developers of chemicapacitor and SAW detection technologies have stated that their technologies are reversible, that is, the sensing units will detect a drop in the concentration of CWAs. But some fiber-optics-based detection systems may not be able to detect a drop in the concentration of agent (after exposure to a higher concentration), and further development may be necessary to overcome that deficiency.
Hysteresis: Additional testing will be necessary to assess how many times the coatings of the various sensors can be used. Alternatively, it may be more feasible simply to replace “coated component” parts, such as those used with the fiber-optics-based systems, after each test.
Challenges Associated with Incorporation into the PETMAN
A number of design considerations are related to physical incorporation of detection technology into the PETMAN system, for example, mounting, location, robustness, and power source.
Mounting of Sensor on PETMAN: It will be a challenge to provide an unobtrusive package that can be mounted at multiple points (50 or more locations) on the mannequin body. The fiber-optics-based sensors appear to be small enough to be mounted in a nearly flush package (less than 0.1 inch high) or possibly woven in a manner similar to the Georgia Institute of Technology adaptive and responsive textile structure (ARTS) fabric system. (See Chapter 5 for a description of this technology.) If SAW or chemicapacitor technology is used, however, the mannequin may require recessed areas to accommodate and minimize the profile of the individual sensing devices.
Resistance to Shock and Vibration: To ensure that a sensor’s response is not affected by exposure to shock and vibration, it may be necessary to envelop it in an inert damping polymeric material, such as silicone sponge.
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If so, damping should not interfere with agent flow to the sensor or with the sensor’s response to the agent.
Powering (Wireless vs Hard Wiring or Tethering of Sensing Units): Multiple options are available for powering the sensor technology. For example, if internal wiring can be made available, a socket capable of receiving a standard dual-in-line package (DIP) could be built into the skin of the mannequin and even recessed to allow a flush surface. The wires under the skin could connect to a readout circuit elsewhere on the body and thereby connect to a wireless interface.The sensor chip could be tethered to the readout circuit via a flexible printed-circuit cable (also called laminated flat flexible cables). The sensor package would be less than 0.1 inch high, and the circuit board could be in a part of the mannequin where it would not interfere with movement. Flexible wiring (less than 0.04 in. thick) would connect to a readout circuit elsewhere on the body and thereby connect to a wireless interface.
Protection from Condensed Moisture or Perspiration: It may be necessary to protect (by design or positioning) the sensors from direct exposure to or contact with condensed water associated with perspiration. Again, interference with agent flow or sensor response must be ensured.
Airflow Across Sensing Units: Sampling analysis may require that air containing an analyte be pulled into and across a sensor’s interaction surface. For example, a fiber-optics-based system may passively absorb and detect the presence of an agent, whereas a SAW or chemicapacitor sensor may require a sample to be pulled into its detection system. If the latter is the required, provisions must be made for creating airflow.
Decontamination or Replacement of Sensors: If it is necessary to decontaminate or replace a sensor or sensor component after each test, provisions must be made for easy access.
Signal Interference: If the system is wireless, it must be ensured that transmitted signals from other components of the PETMAN do not interfere with sensor signals.
COST-BENEFIT ANALYSIS AND TRADE-OFFS
The chemicapacitor, fiber-optics-based, and SAW technologies have the potential to meet the cited requirements for the detection of CWA penetration in the PETMAN system. It is likely that all the sensor technologies will require additional validation, optimization, and modification.
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The hurdles faced by organizations in developing and commercializing a new sensor can be formidable (Table 3.7). For example, although SAW and chemicapacitor technologies have matured to the point where commercially available detection systems are available, their current footprints and profiles may have to be reduced to be practical for PETMAN application. Although preliminary testing of fiber-optics-based technology suggests that it has great potential for this application, additional laboratory validation and modification for successful incorporation into the PETMAN system will be necessary.
It is difficult to accurately estimate the costs associated with the development and optimization of technologies for the PETMAN application. However, the cost to equip a PETMAN with a fiber-optics-based system (a finished product, excluding development and optimization costs) should be relative low, possibly less than $5,000.13 If a SAW or chemicapacitor system is used, the product cost after development could exceed $10,000.14
FEASIBILITY AND POTENTIAL ALTERNATIVES
When assessing the feasibility of a given technology, the following were considered:
Availability and reliability of the technology
Ability to meet the PETMAN requirements, outlined in Tables 3.5 through 3.7
Likelihood of overcoming the design challenges associated with the adaptation of the technology and its incorporation into the PETMAN system
Time to develop and optimize
Cost
Maintenance
The three example technologies discussed—chemicapacitor, fiber-optics-based, and SAW—have the potential to meet the cited requirements for the detection of CWA penetration or permeation in the PETMAN. However, further study, optimization, and design challenges must be addressed before any of those technologies can be effectively used in the PETMAN mannequin application.
Alternatively, the PADs currently used in the MIST system for the cumulative detection of methyl salicylate may be adapted for this appli-
13
Based on presentations by Harmon and Walt in Appendix D.
14
Based on currently available chemical sensor systems from Mine Safety Appliances, Seacoast Science, and others.
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TABLE 3.7 Commercialization of a New Sensor
Phase
Estimated Time to Complete (months)
Estimated Investment ($ millions)
Milestone
1
12-36
—
Laboratory prototype
2
4-6
0.3-0.5
Development and commercialization plan
3
6-10
0.5 -1
Final design
4
6-10
0.5-1
Manufacturing prototype
5
4-6
0.5-1
First production run
6
2-4
0.2-0.5
Market release
Total
22-36
2-4
SOURCE: Taylor, R. F., and J. S. Schultz, eds. 1996. Handbook of Chemical and Biological Sensors, Institute of Physics Publishing, Philadelphia, Table 23.9, p. 573.
cation. Although it is low in cost and could be adapted for the detection of CWAs, the desired advances associated with the PETMAN application—such as detection of penetration or permeation of the garment in 1-s increments—would not be realized. On the basis of consideration of the material presented, the following conclusions were made:
Conclusion 3-1: Both the PADs currently used and the real-time sensors identified have the potential to achieve the PETMAN threshold requirements. The real-time sensors identified also have the potential to achieve the objective requirements of PETMAN. However, several design challenges exist for adapting or incorporating any of these sampling systems into the PETMAN. These challenges include:
Mounting of the sensor onto the mannequin
Resistance to shock and vibration
Powering of the sensor units (wireless versus hard wiring or tethering of sensing units):
Protection from condensed moisture (perspiration)
Airflow across the sensing units
Decontamination and/or replacement of the sensors
Signal Interference
Recommendation 3-1: The existing set of PETMAN performance requirements and the additional criteria identified and described in this chapter should be used for the selection and evaluation of sensors for the PETMAN system.
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Conclusion 3-2: If the PETMAN must operate in the environmental chamber at 125°F (an objective level requirement), a major R&D effort for sensor-coatings could be necessary.
Conclusion 3-3: The hurdles faced by organizations in developing and commercializing a new sensor can be formidable. The cost associated with the development and optimization of technologies for the PETMAN application could be millions of dollars, and the product cost after development could range anywhere from a few thousand dollars to more than $10,000.