Approaches Toward Chemical Wide-Area Decontamination
Neil Hawbaker, Stefanie Smallwood, Jill Ruth, Janlyn Eikenberg, Michael Chesebrough, Lawrence Procell, Kevin Morrissey
The release of a chemical warfare agent (CWA) at staging facilities such as Airports and Seaports of Disembarkation (APODs/SPODs) can hinder operations until the hazard is mitigated. A chemical-wide area decontamination (CWAD) procedure is required to more rapidly mitigate this hazard and will enable forces to maintain operational tempo. However, decontamination of large areas requires a decontaminant which is inexpensive, easily sourced, readily applied, and effective on multiple highly heterogeneous surfaces. Moreover, laboratory studies of asphalt, concrete and soil are complicated by intrinsic variability in the materials making extraction and analysis of performance difficult. In order to overcome traditional challenges faced in testing these types of materials, experiments were performed using smaller coupons, specifically designed to give higher reproducibility and throughput compared to real-world samples. Several decontamination approaches were compared including traditional formulations using standard oxidants, hydrolysis based decontaminants using basic aqueous glycol mixtures, and barrier polymers typically used for trapping volatile organic compounds. Initial studies focused on determining which chemistries and approaches proved the most effective at reducing residual agent. These studies will guide formulation efforts aimed at providing an effective and logistically feasible procedure for CWAD.
Approach and Rationale
1. Standard Oxidant Chemistries
Bleaches, Pool Cleaners
i.e. HTH, Dichlor, Oxone
2. Aircraft Deicer Formulations
Formulated in propylene glycol mix
Permeation, agent solubility
3. High Temperature Hydrolysis
Basic decontaminants applied hot
Reactivity, solubility, permeation
4. Barrier Decontaminants
Sprayable polymer barriers
Limits offgassing, contact hazard
Figure 1. Contamination Mitigation Strategy and Decontamination Approaches for Wide Area Decontamination
The interdependent contamination mitigation (ICM) strategy aims to use several technologies in conjunction to effectively mitigate a CBRN threat. For a large scale wide area decontamination, we aim to explore both polymeric barrier technologies and traditional reactive decontaminants as a means to prepare, respond, and recover from a CBRN event. Initial studies focused on exploring reactive decontaminant formulations through measuring the residual agent post-decontamination. In order to reduce extraction and throughput issues, small panels of calcium sulfoaluminate (CSA) concrete and bitumen roofing shingles were prepared as representative concrete and asphalt samples. An initial set of reactive decontaminants were selected based on bulk availability, logistics, and solubility in decontaminant solution. Reactive decontaminants tested were either standard aqueous oxidants, oxidants formulated in aircraft deicer (propylene glycol) or alkaline solutions applied at a high temperature (40°C).
Figure 2. Reactive decontaminants and materials utilized for an initial decontaminant screen.
Methods for Initial Screening
An initial screen of the selected decontaminants was performed on asphalt and concrete using VX and HD. A 2’’ panel was contaminated with 5µL of agent, and aged for 24 hours. Decontaminant was applied, and then quenched after 4 hours with sodium thiosulfate. Panels were then extracted and the extracts analyzed for residual agent.
Figure 3. Procedure for initial decontaminant reactivity screening.
Results: Reactive Decontamination of Concrete
The initial results show that a large number of decontaminants chemistries effectively remove HD from concrete. For VX, several decontaminants give ~90% efficacy, while ammonium and sodium persulfate proved highly effective.
Figure 4. Residual contaminant after decontamination procedure for HD and VX. Lower numbers indicate better performance.
As simply aging the panel did lead to a substantial reduction in the mass of HD, the log reduction versus the weathering control is a useful analysis metric. A summary of these results is provided in Figure 5. Aqueous decontaminants (blue) proved more effective then the deicer formulations(orange), likely due to the decreased decontaminant solubility. A formulation of KOH applied at 40ׄ°C proved effective but small amounts (5%) of the toxic byproduct EA2192 were detected for VX.
from Weathering Control
Figure 5. Log Reduction versus weathering controls for HD and VX.
Results: Reactive Decontamination of Asphalt Sheets
Initial results demonstrate that decontamination of asphalt sheets is substantially more difficult than decontamination of concrete. Oxone was moderately effective at removing VX from contaminated asphalt sheets and poorly effective at removing HD.
Figure 6. Residual contaminant after decontamination procedure for HD and VX on asphalt sheets
High decontaminant efficacy for both HD and VX on concrete indicates that many decontaminant solutions are highly reactive. Therefore the lack in efficacy on asphalt sheets cannot be attributed to poor reactivity, but rather poor accessibility to the agent entrained within the asphalt panel. The difficulty in decontaminating asphalt is two fold. Firstly both bitumen and the agents are non-polar, allowing for VX and HD to readily soak into the bitumen layer of asphalt. Secondly bitumen ishydrophobic, preventing decontaminant penetration into the material. This can be see in Figure 7, where ammonium persulfate, a highly reactive decontaminated, fails to penetrate into the asphalt.
Figure 7. Images of asphalt sheet with decontaminant solution.
Reactive decontaminants are effective on concrete surfaces. These results demonstrated there aremultiple potential reactive decontaminants which could prove useful for decontamination of HD on concrete. Moreover, several decontaminants gave moderate to good efficacy for decontamination of VX on concrete, particularly ammonium and sodium persulfate. The efficacy of reactive decontaminants on concrete can be attributed to several factors:
- Decontaminant can readily permeate into the material and interact with entrained agent
- Concrete is intrinsically basic, and may act as a basic catalyst and/or activator for several chemistries
- For HD, evaporation from concrete decreases the starting challenge.
Reactive decontaminants cannot access agent entrained in bitumen sheets. Despite the promising reactivity of several decontaminants on concrete, very few decontaminants provided adequate efficacy on the bitumen sheets. This is entirely due to poor mass transport: the aqueous decontaminant solution cannot access the agent entrained within the material. Although these are roofing tile coupons, the principle component, bitumen, is common to any asphalt surface, regardless of the aggregate. For asphalt surfaces, the decontaminant formulations must be adapted to overcome these mass transport issues. Alternatively, the use of barrier technologies may prove to be a better strategy for hazard mitigation on asphalt surfaces.
Future Directions: Barrier Polymers
Another hazard mitigation strategy is the use of barrier chemicals to create a polymer barrier which locks in chemical agent and prevents vapor and contact exposure to unprotected personnel. A variety of polymer chemistries used in soil stabilization, site remediation, and dust suppression have been identified as potential candidates. Current efforts focus on determining how effective these polymers are at reducing the contact and vapor hazard of a contaminated surface. These chemicals may provide an alternative to reactive decontaminant technologies.
Figure 8. A variety of polymer protectant chemicals selected for study.
Future Directions: Rollover Contact Testing
The ability to pass through a contaminated area without the need for thorough decontamination of all vehicles and equipment is important. The purpose of this experiment is to determine whether a wide area decontaminant is needed to reduce the contact hazard posed to vehicles traveling through a contaminated area. The contact hazard posed by a vehicle rollover can be assessed using a short-duration, high- pressure contact of a panel with a styrene-butadiene rubber (SBR) sampler. Current work focuses on developing a way to measure that contact hazard. Through using an arbor press with a rubber sampler, we aim to simulate that rollover event and to measure the approximate contact transfer to that material.
Figure 8. (left) Figure from ref 1. (right) Arbor Press Design
Future Directions: Vapor Offgassing
Analysis of the post-decontamination vapor hazard is a key goal for analysis of decontaminant performance for both the reactive and barrier decontaminant technologies. However, no studies have attempted to utilize the vapor microchamber and solid sorbent tube system to analyze vapor off-gassing from concrete and asphalt. In order to design an effective pull schedule for the vapor test, a vapor screening test has been performed to provide an initial estimate of the vapor concentration profile. This is the first step in analysis of the post-decontamination vapor hazard for both barrier and reactive decontaminant systems.
Figure 7. Vapor profile for HD on steel, bitumen and concrete.
This research was funded and supported by the Defense Threat Reduction Agency (DTRA)/Joint Science and Technology Office (JSTO) under project CB10662. The authors thank Drs. Charles Bass and Glenn Lawson (DTRA JSTO) for their support and helpful discussions. The views expressed in this abstract are those of the authors and do not necessarily reflect the official policy or position of the Department of Defense or the U.S. Government.