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News :: Miscellaneous |
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CDC Proposes Reduced Exposure Limits For VX Nerve Gas |
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by ML
(No verified email address) |
11 Jan 2002
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The Centers for Disease Control has proposed reduced environmental exposure limits for VX nerve gas. Some 1,700 tons of VX nerve gas is stored at the Newport Army Ammunition Depot, approximately 50 miles east of Urbana, IL, where it is awaiting disposal. |
The Centers for Disease Control has proposed reduced environmental exposure limits for VX nerve gas. Some 1,700 tons of VX nerve gas is stored at the Newport Army Ammunition Depot, approximately 50 miles east of Urbana, IL, where it is awaiting disposal.
The aftermath of Sept. 11 has brought increased security to Newport, but residents near the depot just across the state line in Indiana are eager to have the gas gone. Delays in construction mean that the first actual disposal of VX, one of the most toxic substances known, is years away.
Army units have augmented the regular depot guard force, which was authorized to use deadly force against intruders or other threats to the depot even before the events of sept. 11. It is said that the VX canisters, large metal cylinders holding several tons each of VX, will be moved to a more secure facility on the depot. The cylinders have been housed in above-ground metal warehouses.
The attacks of Sept. 11 have made clear that these buildings provide no protection against such a strike. Airspace around the depot has been restricted and there are rumors that anti-aircraft weapons are part of the Army deployment, although this has not been confirmed. Even so, there is no sure defense against suicidal terrorism. The cylinders are likely being moved to separate earthen-bermed bunkers on the depot which will provide some increased protection, but storage conditions of higher humidity may result in increased corrosion of the cylinders and increase the possibilities of leaks.
With all this going on, the Centers for Disease Control has proposed lowering the environmental and occupational exposure levels for those working around VX. The proposal is part of a larger look at exposure level hazards for all of the U.S. chemical warfare agents, which are all due to eventually be destroyed as part of the provisions of Chemical Weapons Convention. For more information, follow this link:
http://www.clw.org/coalition/poison/poison.htm
Several points about the CDC’s proposal should be made. The first is will this proposal be adopted or will the Army oppose these lower limits of occupational and environmental exposure?
Another is that the level of toxicity of VX had to be estimated because of a lack of accurate scientific data on VX. What the CDC has done is developed a model that indicates that VX is 36 times as potent as another one of the U.S. chemical agents, GB.
The final point is that, given this level of toxicity, there is no current technology to accurately measure such a small level in the environment. The CDC suggests some stop-gap measures to deal with this problem until better technology becomes available. If one is a worker, guard, or nearby resident, this cannot be reassuring. The author is glad that he resides upwind from Newport and hopes that these weapons of mass destruction are quickly disposed of in a safe manner.
Below is a relevant excerpt form the entire CDC document, available at the Cryptome website:
http://cryptome.org/cdc010802.txt
3.
Airborne Exposure Limits for VX Since the toxicity data for VX are inadequate, CDC proposes derivation of the VX WPL, STEL, and GPL from the calculated exposure limits for GB, using a relative potency of 12 compared to GB and application of a modifying factor of 3 for the incomplete VX data set. This approach, which effectively results in a relative potency of 36, is the same as that recently proposed by the EPA NAC/AEGL committee (20).
CDC proposes that the WPL for VX should be decreased to 1 x 10-\6\ mg/m\3\ (a factor of 10 lower compared to the current value and the U.S. Army's recommendation). Additionally, CDC proposes VX STEL of 4 x 10-\6\ mg/m\3\. CDC proposes a VX GPL of 6 x 10-\7\ mg/m\3\, expressed as a 24-hour time-weighted average. The VX GPL, derived from the GB GPL to which the relative potency of 12 and a modifying factor of 3 was applied, was initially calculated as 3 x 10-\8\ mg/m\3\. However, currently available monitoring methods are unable to reliably detect VX at this concentration. CDC believes that reliable monitoring is a crucial aspect for implementing the exposure limits and therefore proposes to increase the GPL to a concentration that can reliably be monitored. The CDC proposes 6 x 10-\7\ mg/m\3\ for the VX GPL, a value that is both protective and technically feasible to monitor.
The proposed VX GPL of 6 x 10-\7\ mg/m\3\, used in conjunction with the existing perimeter montoring programs, will be protective because long-term releases of VX are unlikely. Routine maintenance and monitoring procedures implemented for worker safety near the potential sources of releases (where concentrations potentially would be higher than at the perimeter) prevent long-term releases. At demilitarization sites, perimeter monitoring results for 12-hour samples are typically available within 72 hours. Detections of chemical agent above the action level result in (1) an investigation to determine the source of the vapor and (2) corrective action to eliminate the source. In the derivation of the GPL in accordance with EPA methodology, the exposure period of the critical study is adjusted for a continuous 7-day exposure for the general population. The perimeter monitoring results at demilitarization sites are obtained within 72 hours (3 days) following sampling. To correct the assumption of continuous exposure for 7 days, a factor of 3 days potential exposure per 7 days was applied to the calculated VX GPL of 3 x 10-\8\ mg/m\3\. Additionally, in the derivation of the GPL, an uncertainty factor of 10 was applied to extrapolate from sub- chronic to chronic exposures. Since a chronic exposure is unlikely, this extrapolation would not be needed. These calculations result in adjusting the initially calculated VX GPL of 3 x 10-\10\ mg/ m\3\ to 6 x 10-\7\ and support the conclusion that the proposed GPL of 6 x 10-\7\ is protective of human health. This adjustment of the VX GPL was made in acknowledgment of the technical limitations of current air monitoring methods, while assuring that the GPL would be protective of public health.
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The expert group members did not object to the Army-proposed IDLH values for VX (0.01 mg/m\3\), although there was little specific discussion among the panel. In accordance with relative potency approach used for WPL and GPL (potency factor of 12 with a modifying factor of 3), CDC proposes a VX IDLH of 0.003 mg/m\3\.
4.
Proposed Implementation of the VX GPL Current data suggest that air monitoring at the proposed VX GPL concentration is on the fringe of technical feasibility for current methods. CDC investigated this issue with representatives from NIOSH, the U.S. Army, and other independent consultants. CDC representatives heard compelling evidence that current VX air monitoring methods may need further development. At the proposed VX GPL, the mass of other ambient organic materials normally found in the air (background chemicals) will greatly exceed the mass of VX to be measured. These background materials cause analytical problems in discerning and quantifying VX.
Halting disposal until improved monitoring methodology can be developed presents at least three grave problems:
a. There is greater cumulative risk from continued storage compared to continued disposal under the existing exposure limits.
b. The desired level of sensitivity and selectivity may not be easily attainable.
c. The United States has treaty obligations to complete the disposal within a specified time.
Inasmuch as delay in disposal presents an unacceptable risk to public health and safety, CDC proposes the following interim measures regarding monitoring at the proposed VX GPL:
a. CDC proposes a multifaceted research program to look at commercially available systems that have the potential to improve air monitoring at the proposed VX GPL. Further, CDC recommends that the Army use one or more Ph.D.-level analytical chemist(s) who have air monitoring experience to direct this program.
b. CDC proposes suspension of the 20% action level for the VX GPL until the monitoring methodology can be improved.
c. For all demilitarization sites handling VX, CDC proposes that all qualitative responses above a 3:1 signal-to-noise ratio for VX from perimeter stations be evaluated (i.e., those that are below the limit of quantification for VX). When VX is qualitatively detected, action should be taken to investigate the possible sources of these responses.
Reference: |
See also:
http://www.cryptome.org/
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