Medical Aspects of Chemical Warfare (2008) - The Black Vault

History of the Chemical Threatthey present an immediate but short-lived threat. Theseagents are referred to as “nonpersistent” because theyvaporize rapidly after delivery. Alternatively, agentssuch as VX and sulfur mustard tend to fall largely indroplets with less vaporization and remain on exposedsurfaces for at least 24 hours. These agents are called“persistent.”Wind is an important consideration in determiningthe distribution of an agent cloud. As in any fluidsolidinterface, the earth’s surface exerts a drag onwind currents. Under a moving cloud, volatile agentconcentrations can be expected to mix more slowly atthe surface and increase in concentration with height.Vegetation further exacerbates this drag and increasesthe height of the protective layer in which agent concentrationis low.Formulation is also used to manipulate the fate ofan agent. Soman, VX, lewisite, and sulfur mustard canbe mixed with thickeners of high molecular weight toincrease droplet size and thereby decrease primaryvaporization. Such additives are generally used topromote efficient agent deposition on the target site.Thickeners can also increase agent persistence andmay hamper decontamination efforts. Adding silicapowder to sulfur mustard (“dusty mustard”) canpropel the agent in a dust cloud. Stabilizers increaseagent shelf life.Nonpersistent AgentsTable 4-3Comparative Volatility of ChemicalWarfare AgentsAgent volatility (mg/m 3 ) at 25°CHydrogen cyanide (HCN) 1,000,000Sarin (GB) 22,000Soman (GD) 3,900Sulfur mustard 900Tabun (GA) 610Cyclosarin (GF) 580VX 10VR (“Russian VX”) 9Data source: US Departments of the Army, Navy, and Air Force.Potential Military Chemical/Biological Agents and Compounds.Washington, DC: Headquarters, DA, DN, DAF; December 12,1990. Field Manual 3-9. Naval Facility Command P-467. Air ForceRegulation 355-7.In tactical use, the threat of nonpersistent, volatileagents, such as HCN or sarin, is greatest to the respiratorysystems of unprotected soldiers. A sudden,heavy bombardment of these agents may affect manycasualties if unmasked soldiers are caught by surprise.When used against an unprotected force, nonpersistentagents are particularly effective in generating casualties,thereby creating breakthrough points in enemyfront lines. Iraq successfully used nonpersistent nerveagent in counterattacks against Iranian forces during1988. 81 Nonpersistent agents can be used to slow enemyadvancement by forcing the enemy to wear protectiveequipment. They can also circumvent an enemy’s protectionagainst conventional high-explosive munitionsand may be used in night attacks to harass troops.Persistent AgentsGiven favorable weather conditions, the use ofpersistent agents such as mustard and VX may pose athreat for many days. Such agents can deny or interferewith enemy occupation of terrain or equipment useand could be used defensively to protect vulnerableflanks. However, although persistent agents can slowenemy movement, they can also hamper the movementof friendly forces through a contaminated area.Delayed casualties may occur even among protectedtroops operating in a contaminated area for an extendedperiod. Hence, persistent agents, which canlinger as coatings or in puddles for weeks, may not bethe agents of choice when occupation of territory byfriendly forces is imminent.Chemical land mines that disperse persistent agentmay be used in conjunction with military barrier systemsto complicate breaching or clearing the barriers.The mines are typically based on high-explosive minedesigns, with several pounds of agent substituted formost of the explosive charge. High-explosive landmines cause contaminated open wounds, primarily onlower extremities, that must be properly decontaminated;decontamination could be more difficult whenpersistent agents are used.Sulfur mustard, a blistering agent, tends to linger onskin, promoting percutaneous absorption, and offers strategicbenefits besides those considered above. It was usedvery effectively both during World War I and the Iran-IraqWar to generate thousands of casualties. Although deathsamong unprotected sulfur mustard exposure victimsare relatively few, mustard casualties can overwhelmmedical treatment facilities. 87 Survivors of other agentexposures stabilize relatively quickly, but mustard lesionsdemand months of medical care. This was the fateof many thousands of unprepared or poorly equippedIranian recruits exposed to sulfur mustard agent.Underscoring the importance of ambient tempera-135