Persistent agents

HL is a persistent agent depending on pH and moisture and has been known to remain active for up to 3 years in soil. 

For military purposes, unmodified carbamate nerve agents are classified as extremely persistent. Agents have negligible vapor pressure and they will not evaporate. Depending on the size of the individual particles and on any encapsulation or coatings applied to the particles, they can be reaerosolized by ground traffic or strong winds. 

Persistent Agent Chemical agents that do not hydrolyze or volatilize readily, such as VX and HD. At the time of release, this agent can produce casualties for an extended period of time up to several days. Usually, it has a low evaporation rate. Since its vapor is heavier than air, its vapor cloud will hug the ground and accumulate in low areas. It is an inhalation hazard, but extreme care should be taken to avoid skin contact as well. 

DETAILS - VX, like most other nerve gases, originated from insecticide research, which in this case, was done in Britain in the late 1950 s. Unlike Sarin, VX is a persistent agent - meaning it can stay on target... 

We had to reckon with the British, in the defence of their homeland. .. using every weapon and all means available... that might hold out even the slightest hope of success. We had to allow for the possibility of our troops being attacked... with non-persistent agents... as well as with vesicants.40... 

The Division has undertaken to supply and maintain the non-persistent agent sampling equipment. To mention only a few of the most important items, it has supplied over one hundred recording milliammeters of the Esterline-Angus and General Electric types, 46 Dickinson meters,... 

Evidently, ANA (first described by G.J. Friou et al. in 1957) belong to the natural autoantibodies which are continuously stimulated by a still unknown mechanism (possibly a persisting agent) in certain diseases. However, this antibody phenomenon is inconsistent and neither organ- nor disease-specific. ANA can be visualized by immunofluorescence in cryostat tissue sections of the rat liver and rat kidney as a homogeneous (s. fig. 5.10), speckled (s. fig. 5.11), circular or nuclear fluorescence pattern. This allows conclusions to be drawn as to the specificity of antinuclear antibodies and in some cases as to the nature of the underlying disease as well. 

VX is absorbed through the skin and respiratory system. Because it is nonvolatile, it may remain in place for weeks after dispersion and cause casualties. Thus, it is classified as a persistent agent. Although VX does not pose a major inhalation hazard in usual circumstances, by the inhalation route it is estimated to be 10 times as toxic as sarin. It is hydrolyzed by the enzyme organophosphorus (OP) hydrolase. 

Sulfur Vesicants are persistent agents and, under proper conditions, remain hazardous in soils for several years. Thickened agents last significantly longer. 

Arsenical Vesicants are persistent agents. However, agent vapors rapidly react with high humidity to lose most of their vesicant properties. Limited solubility slows the hydrolysis of liquid agents. 

Choking Agents are nonpersistent. Cold weather may decrease the rate of volatilization of any liquids present and increase persistency. Agents absorbed into porous powders may be significantly more persistent than normal. Decomposition products from the breakdown of some Choking Agents can pose a persistent hazard. 

Persistency is an expression of the duration of effectiveness of a chemical agent. This is dependent on the physical and chemical properties of the agent, weather, methods of dissemination, and conditions of the terrain. Under battlefield conditions, non-persistent agents generally lose their effectiveness approximately 10 to 15 minutes after deployment. See also Relative Persistency. 

The fate of HD in the environment is determined by its chemical and physical properties. Observations of persistence and degradation products from both field and laboratory studies support the characterization of HD as a persistent agent. As noted, sulfur mustard is a liquid at ambient temperatures the vapor pressure is low (0.11 mmHg at 25°C), but sufficient for mustard to be in the air immediately surrounding droplets of the liquid. The primary dissipation mechanism for HD from soil is evaporation. Sulfur mustard vapor is 5.5 times heavier than air, and evaporation or volatilization from surfaces or soils is projected to require days at temperatures above its freezing point (Puzderliski, 1980). Below its... 

Non-persistent agents, such as sarin, soman and tabun, disperse rapidly after release and present an immediate short duration inhalational hazard but may be made persistent by a thickening agent , such as ethyl methacrylate. In contrast, persistent agents, such as VX, continue to be a contact hazard and may be absorbed through the skin or can vaporize over a prolonged period to produce an inhalation hazard. 

Phosgene can be disseminated by aircraft, from pressurized containers and by bombs and shells. The gas is rapidly dispersed by the wind although, as it is heavier than air, it tends to accumulate in low-lying areas and dangerous concentrations may occur in cellars and trenches. Despite this, phosgene is classified as a non-persistent agent likely to be used to kill and incapacitate rather than to deny access to ground. 

Collect and identify fallout or persistent agents, BW and CW, from soil, in water, on surfaces of objects, and in and around buildings. 

Chemical Hazard Prediction Ground Burst Non-Persistent Agent... 

Chemical Hazard Prediction Air Burst Persistent Agent Type B Attack Windspeed. .10 kmph... 

Nerve agent VX is a persistent agent which presents both a vapor and a percutaneous threat. VX is not very volatile, so it presents much less vapor hazard than GA and GB however, it is 100 times more toxic by the percutaneous route. Therefore, if VX is aerosolized due to an explosive release, it presents a percutaneous downwind hazard. Thermal decomposition rates of VX are 1.5 hours at 200°C (392°F), 4 minutes at 250°C (482°F), and 36 seconds at 295°C (563°F). In practical terms, a toxic dose of VX is more likely to result from skin rather than respiratory exposure however, all nerve agents are sufficiently volatile to pose an inhalation hazard. At agent concentrations of 30 mg/m3 or greater, median lethal inhalation doses can be attained in a few minutes. 

Type A Non-persistent agents, such as G-agents, create a vapor hazard. 

Type B Persistent agents such as V-agents contaminate surfaces. 

A. Persistent agents continue to present a hazard for considerable periods (days) after delivery by remaining as a contact hazard, or by slowly vaporizing to produce a hazard by inhalation. 

Used against poorly-armed and trained insurgents, the imperial powers rapidly learnt that gas was a devastating weapon. Persistent agents like mustard could make favourite ambush positions untenable for weeks. Tear gas and smoke weapons, especially if used from the air, forced the enemy into the open where he could be more easily picked off. By 1925 the French and Spanish were employing poison gas in Morocco, and it had become clear that chemical warfare had found a new role, as a tool by which major powers could police rebellious territories. 

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