Developing Health-Based Pre-Planning Clearance Goals for Airport Remediation Following Chemical Terrorist Attack: Introduction and Key Assessment Considerations

Figures & data

Table 1 Response and recovery phases to a chemical terrorist attack. Current assessment focus is on developing guidelines to direct Remediation/Cleanup and Restoration/Re-occupancy decisions and activities.^a

Response and recovery
		Remediation/Cleanup^b,c
Notification	First response	Characterization	Decontamination	Clearance	Restoration/Reoccupancy
Receive information on chemical incident Identification of suspect release sites Notification of appropriate agencies	Initial threat assessment HazMat and emergency actions Forensic investigation Public health actions Initial environmental sampling Determine agent type and concentration Risk communication	Detailed characterization of CWA or TIC Characterization of affected site Site containment Prompt source reduction Continue risk communication Characterization, environmental sampling and analysis Initial risk assessment Clearance goals	Decontamination strategy Remediation Action Plan Worker health and safety Site preparation Continued source reduction Waste disposal Decontamination of sites, items, or both Verification of decontamination parameters	Clearance environmental sampling and analysis Clearance decision	Renovation Reoccupation decision Potential long-term environmental and public health monitoring
^aDerived from Figure 1–1 in DHS (2009a); ^bWithin 24 hours post-release, full operation restored to all 3 Tokyo (Japan) subway lines in which nerve agent GB had been released by chemical terrorists on March 20, 1995; phased operations allowed full-service restoration on 2 subway lines within 10 hours post-release (Komiya and Kamakura 1995; Lillibridge 1995; Tu 2002, 2007; Ember 1995); ^cWithin 16 days post-release, full re-occupancy of all homes and businesses previously evacuated following 70-ton chlorine release from overturned train tank car in Graniteville, SC, on January 6, 2005; phased operations allowed re-occupancy of certain residences within 6 days post (Mitchell et al. 2005).

Table 2a Chemical and physical properties of CWAs and TICs.

Properties of CWAs and CAS	Tabun^a (GA)	Sarin^b (GB)	Soman^c (GD)	Cyclosarin^d (GF)	VX^e	Sulfur Mustard^f (HD)
number	77-81-6	107-44-8	96-64-0	329-99-7	50782-69-9	505-60-2
Chemical structure
Corrosivity
• pH	Nonaqueous	Nonaqueous^h	Nonaqueous	Nonaqueous	Nonaqueous	Nonaqueous
• Steel corrosion (inches per year)^g	4.08 × E^−4 @ 65°C	Stabilized GB can be stored in steel for ≤10 y @ 20–5°C	1.2 × E^−4 @ 65°C	6.36 × E^−4 @ 65°C	High-purity VX stable in steel	1.2 × E^−3 @ 65°C
Ignitability
• Flash point °C (F)	78 (172.4)^i	>138 (280.4)^j	121 (249.8)^j	94 (201.2)^j	159 (318.2)^j	105 (221)^g,i
• Oxidizer	No	No	No	No	No	No
Reactivity
• Violent reaction with H2O?	No^i	No^i	No^i	No^i	No^i	No^i
• Hazardous quantities of toxic gases, fumes, or vapors generated when mixed with H2O?	No^k	No^k	No^l	No^g	No^l	No^i
• Reactive –S2 or –CN bearing waste?	Potential^k,m	No^k,n	No^n	No^n	No^g	No^i
• NFPA rating (0 to 4)	1^i	1^i	1^i	1^i	1^i	1^i
Boiling point °C (F)	245 (473)^j	158 (316.4)^j	198 (388.4)^j	239 (462.2)^j	298 (568.4)^j	218 (424.4)^o,j
Melting point °C (F)	−50 (−58)^j	−56 (−68.8)^j	−42 (−43.6)^j	−12 (10) freezes at −30 (−22)^g,j	−39 (−38.2) calculated^j	14.45 (58.01)^g
Molecular weight	162.13^j	140.10^j	182.178^j	180.2^j	267.37^j	159.08^j,p
Physical state	Liquid (colorless to brown)^j	Liquid (colorless)^j	Liquid (colorless)^j	Liquid^j	Liquid (oily, amber-colored)^j	Liquid or crystal (colorless, oily liquid or yellow prisms)^p,j
Specific gravity (g/mL)	1.07 @ 25°C^j	1.10 @ 20°C^j	1.02 @ 25°C^j	1.13 @ 20°C^j	1.01 @ 20°C^j	1.27 @ 25°C^g
Vapor density (air = 1)^j	5.63	4.86	6.33	6.2	9.2	5.4
Vapor pressure (mm Hg)^j	0.037 @ 20°C	2.10 @ 20°C	0.40 @ 25°C	0.044 @ 25°C	0.0007 @ 20°C	0.072 @ 20°C
Volatility (mg/m^3 at 25°C)	497^g	18700^g	3930^g	898^g	12.6^g	906^g
Water solubility (g agent/g H2O)	7.2g/100g @ 20°C^g	Miscible^g	2.1g/100g @ 20°C^g	3.7g/100g @ 20°C^g	3.0g/100g @ 25°C^o	0.92g/100g @ 22°C^g practically insoluble

Table 2b Chemical and physical properties of CWAs and TICs.

Properties of TICs And CAS number	Hydrogen Cyanide (AC) 74-90-8	Cyanogen Chloride (CK) 506-77-4	Phosgene (CG) 75-44-5
Chemical Structure	H-CN	CN-Cl
Corrosivity
• pH	N/A	N/A	N/A
• Steel corrosion (inches per year)^q	< 0.002 @ 25, 50 75, and 100°C	< 0.02 @ 25°C	<0.002 @ 25°C (when dry); >0.05 @ 25°C (when containing 10% H2O)
Ignitability
• Flash Point °C (F)^g	−18 (−0.4)	Nonflammable	Nonflammable
• Oxidizer	No	No	No
Reactivity
• Violent reaction with H2O?	No^g,r	No^s	No^s
• Hazardous quantities of toxic gases, fumes, or vapors generated when mixed with H2O?	Potential^g,t	Potential^u,v	Potential^g,w
• Reactive –S2 or –CN bearing waste?	Potential^x	Potential^u,v	No^s
• NFPA rating (0 to 4)	2^y	2^s	1^y
Boiling point °C (F)	25.6 (78.08)^z	12.8 (55)^g,z	8.2 (46.76)^z
Melting point °C (F)	−13.4 (7.88)^z	−6.9 (19.58)^g,z	−128 (198.4)^z
Molecular weight	27.03^z	61.48^g	98.92^z
Physical state	Liquid or gas (bluish liquid or colorless gas)^z	Liquid or gas (colorless)^g,k	Gas^z
Specific gravity (g/mL)	0.68 @ 25°C^g	1.19 @ 20°C^p	1.38 @ 20°C^l
Vapor density (air = 1)	0.941^z	2^p	3.4^z
Vapor pressure (mm Hg)	746 @ 25°C^g	1010 @ 20°C^u	1215 @ 20°C^z
Volatility (mg/m^3 at 25°C)	1.08 × 10^6 g	2.62 × 10^6 g	7.46 × 10^6 g
Water solubility (g agent/g H2O)	Miscible^g	71.4g/1200g @ 20°C^g	Limited solubility in water^g
^aEthyl N, N-dimethylphosphoroamidocyanidate; ^bIsopropyl methylphosphonofluoridate; ^cPinacolyl methylphosphonofluoridate; ^dO-cyclohexyl methylphosphonofluoridate; ^eO-ethyl-S-(di-isopropylaminoethyl) methyl phosphonothiolate; ^fBis-(2-chloroethyl) sulfide; ^gfrom DA (2005a); ^hSarin hydrolyzes to yield decomposition products that include hydrogen fluoride and methylphosphonic acid (Talmage et al. 2007a,b).; ^iU.S. Army Edgewood Chemical Biological Center (ECBC 2008); ^jNational Research Council, Committee on Toxicology (NRC/COT 2003); available at www.nap.edu; ^kO’Neil et al. (2001); ^lClark (1989); ^mWaste will require monitoring to determine potential reactivity. When undiluted GA liquid is treated with high-pH chlorine decontaminant solutions, cyanogen chloride may be generated as an intermediate. Any resulting CK concentrations depend on reaction temperature, reaction yield, and other variables (Columbia University Press 2001–2007); ^nDoes not contain –CN anion, or nitrogen or sulfur (needed to form cyanide and sulfide-bearing compounds, respectively); ^oNational Library of Medicine, Specialized Information. Services, available at http://www.sis.nlm.nih.gov/enviro/chemicalwarfare.html; ^pNational Library of Medicine, Toxicology Data Network, ToxNet, available at http://toxnet.nlm.nih.gov/; ^qHamner (1974); ^rUnstabilized or impure hydrogen cyanide can polymerize violently, especially at elevated temperatures (≥50°C) in a closed vessel with generation of gaseous products that can result in pressure rupture to a storage vessel. The conditions are unlikely under the current release scenario. Long storage can degrade stabilizers and lead to container rupture. See Aaron (1996); ^sNIOSH Emergency Response Safety and Health Database, Emergency Response Card; available at www.cdc.gov/niosh/ershdb; ^tDepends on agent concentration and solution pH. As HCN vapor reacts with plain water, it disproportionates into ions (H30^+ and CN^−) that form an acidic solution. HCN is not very water-soluble and cannot disproportionate in acidic waters. Thus, cyanide-bearing fumes would not be evolved. In high concentrations, HCN can begin to cyclize and form dark-colored and (violently) unstable compounds. This is a problem in closed vessels (see footnote r). ^uLewis (2000); ^vDepends on agent concentration and solution pH. If water were introduced as mixed with a decontamination agent which is normally caustic and contains some oxidant, gases, fumes, or vapors may not be an issue. Water of a basic pH will capture cyanide and not release cyanide. If basic solution containing cyanide is acidified, HCN or HCl could evolve, depending on solution pH; ^wDepends on agent concentration and reaction chemistry of solution. Decomposition of phosgene in water yields HCl and CO2. Although HCl is soluble in water up to 30% (after which HCl in water is saturated and could evolve), presence of the CO2 reaction product will tend to reduce HCl solubility in water; ^xWaste will require monitoring to determine potential reactivity. Although hydrogen cyanide (HCN) does not react to liberate dangerous quantities of toxic gas when exposed to pH conditions between 2 and 12.5, undilute HCN is, in and of itself, a lethal cyanide-bearing gas; ^yNFPA (1994); ^zNational Research Council, Committee on Toxicology (NRC/COT 2002); available at www.nap.edu.

Table 3 Properties of principal CWA degradation products (commercial compounds are provided for comparison).

Degradation product^a (formula; CAS number)	Parent CWA	Persistence^b	Acute toxicity (oral LD50) (mg/kg)	Toxicity rating^c	Vapor pressure^d (mm Hg)	Water solubility^d (mg/L)
MPA (solid) (CH5O3P; 993-13-5)	GB, GD, GF, VX hydrolysis	High	5000 (rat) >5000 (mouse)^a	Slightly toxic (#2)	2 × 10^−6	> 1.0 × 10^6
EMPA (liquid) (C3H9PO3; 1832-53-7)	VX hydrolysis	Moderate	Considered similar to IMPA^a	Slightly toxic (#2)	3.6 × 10^−4	1.8 × 10^5
EA 2192 (solid) (C9H22NPO2S; 73207-98-4)	VX hydrolysis (pH 7–10)	Moderate	0.630 (rat)^a	Supertoxic (#6)	Not detectable; 5.1 × 10^−6 (est.)	Infinitely soluble
IMPA (liquid) (C4H11PO3; 1832-54-8)	GB hydrolysis	High	6070–7650 (rat) 5620–6550 (mouse)^a	Slightly toxic (#2)	1.2 × 10^−2 (est.)	5.0 × 10^4
Thiodiglycol (liquid) (C4H10O2S; 111-48-8)	HD hydrolysis	Moderate	6610 (rat)^a	Slightly toxic (#2)	2 ×10^−5	Miscible
Aspirin (50-78-2)	Not applicable	__	50–500^e	Very toxic (#4)^e	2.5 × 10^−5 (calc.)	4.6 × 10^3
Table salt (NaCl; 7647-14-5)	Not applicable	__	3750 (rat)^e	Moderately toxic (#3)^e	1.0 at 865°C	3.6 × 10^5
Saccharin (soluble) (128-44-9)	Not applicable	__	5000–15000^e	Slightly toxic (#2)^e	Sublimes in vacuum	4.3 × 10^3
^aDegradation products selected on the basis of environmental persistence, toxicity, or both from Talmage et al. (2007a, Table 1, Ch. 4); Munro et al. (1999); Reddy et al. (2005); Capacio et al. (2008, Table 19.2, Ch. 19);
^bPersistence ranking based on chemical/physical properties and degradation data/estimates; mod = weeks to months, high = months to years (Talmage et al. 2007a).
^cKlaassen et al. (1986, Table 2–2, p. 13);
^dMunro et al. (1999); Howard and Meylan (1997); Michel et al. (1962); Rosenblatt et al. (1995); Hazardous Substances Data Bank, U.S. National Library of Medicine, Bethesda, available at www.toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?index.html;
^eGosselin et al. (1984).

Figure 1 Non-persistent compound: Decontamination and clearance verification.

Figure 2 Persistent compound: Decontamination and clearance verification.

Figure 3 Effects of natural attenuation only (e.g., no active decontamination) on persistence of liquid GB spike on indoor airport surfaces; 1 μl droplet (containing 910 μg GB) (Love et al. 2009; Love et al. in review). The percent of GB remaining is depicted relative to the amount of GB initially applied to the surface. (a) Short-term persistence (within 1 week). (b) Longer-term persistence (within 1 year).

Figure 5 Effects of natural attenuation only (e.g., no active decontamination) on persistence of liquid VX spike on indoor airport surfaces; 1 μl droplet (containing 990 μg VX) (Love et al. 2009; Love et al. in review). The percent of VX remaining is depicted relative to the amount of VX initially applied to the surface. (a) Short-term persistence (within 1 week). (b) Longer-term persistence (within 1 year).

Figure 4 Effects of natural attenuation only (e.g., no active decontamination) on persistence of liquid HD spike on indoor airport surfaces; 1 μl droplet (containing 790 μg HD) (Love et al. 2009; Love et al. in review). The percent of HD remaining is depicted relative to the amount of HD initially applied to the surface. (a) Short-term persistence (within 1 week). (b) Longer-term persistence (within 1 year).

Table 4 Half-lives of liquid VX and HD in hydrolysis or oxidation solutions with estimated agent remaining after 48 hour degradation (initial unit concentration of 1.0 mg/cm²).

CWAs in	Half-life	Estimated agent remaining after 48 hr degradation for an initial unit
solution	(minutes)	concentration (1.0 mg/cm^2)
VX Hydrolysis
1.25M NaOH	1.8^a	<4.23E-304 (mg VX/cm^2)^b
0.25M NaOH	10.8^a	5.53E-81 (mg VX/cm^2)
0.1M NaOH	31^a	1.09E-28 (mg VX/cm^2)
0.01M NaOH	198^a	4.19E-05 (mg VX/cm^2)
0.001M NaOH	1248^a	2.02E-01 (mg VX/cm^2)
Pure Water	3600^a	5.74E-01 (mg VX/cm^2)
Unbuffered Water	4680^c	6.53E-01 (mg VX/cm^2)
Sulfur mustard (HD) Oxidation
>20% H202	≤2^d	< 4.23E-304 (mg HD/cm^2)^b
^aYang et al. 1994; ^bThis value represents limit of software computational capability; actual value is less; ^cYang 1999; ^d Wagner and Yang 2002.

Figure 6 2-day hydrolysis degradation of liquid VX in NaOH solutions and water (half-life determinations from experimental data of Yang et al. 1994 and Yang 1999 applied to a unit concentration).

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