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This is the training version of the Rule of Thumb Sheets related to chemical agent releases. Three pages are covered here:
The Rules of Thumb, as the name suggests, are not intended to be rigourously applied; every situation will be different, and the individual will need to use judgement. It is hoped, however, that the Rules of Thumb may provide some guidance for making the right decisions.
In this training version, the rules of thumb are accompanied by further information and explanatory notes giving the rationale for the rule which are in some cases not presented on the handout versions of the Rules of Thumb. An External Resources section is also provided which includes links to some possibly useful external resources that give further information on certain topics.
A note on terminology: In the Rules of Thumbs documents the term agent cloud is used throughout to refer to either a cloud or a plume of a chemical agent. Purists may object, but cloud conveys the meaning perfectly clearly in context.
Indicators of Chemical Attack Include:
In the environment
- Some chemicals will quickly kill off plant life, so unusual patterns of dead grass, flowers, etc. may indicate dissemination of chemical warfare agents.
- Chemical agents may kill or drive off insects - nerve agents may act sufficiently rapidly that large numbers of dead insects may be seen on the ground.
- Chemicals that injure humans will usually affect animals, although sometimes in different ways and at different speeds than humans. If groups of animals seem to be dying at the same time without obvious cause, this suggests a chemical attack.
Casualties
- Chemicals tend to affect people at roughly the same time, so release of a chemical agent will tend to produce a group of casualties at locations near the release. An exception to this is the mustard agents. Due to the latent period between exposure and appearance of symptoms for mustard casualties, it is possible that casualties would appear at separated locations to which they had travelled after exposure, possibly over a period of several hours.
- Chemicals used to poison food or drink will affect only those eating or drinking the tainted materials; the rapid action of most poisons will tend to produce casualties at/near the dining location without affecting those (e.g., servers, cashiers, etc.) who don't eat.- Chemicals disseminated as vapors or aerosols will tend to move with the wind if outside, producing a sequential appearance of casualties on exposure to a chemical agent.
- Chemicals disseminated as vapors or aerosols inside a structure will affect those entering the structure.
Other
- Not usually reliable, as incidents involving casualties usually involve diverse odors, but some agents do have distinctive odors. If possible, simulants should be obtained to allow familiarization.
- no rain or watering going on
- There would ordinarily be no reason for a crop duster to appear over a residential area or for a lawn service to be firing up their sprayers in a parking lot.
- The liquids or solids may be a chemical agent.- Remember in any incident involving an explosive device that there may be additional devices set for later times to injure responders.
- You will simply become another casualty- In the Tokyo Subway attack, deputy station masters Kazumasa Takahashi and Tsuneo Hishinuma soaked up the liquid with newspapers and actually picked up at least one of the sarin-containing bags and put it into a plastic bag. Their heroic actions undoubtedly saved many lives by confining at least some of the agent, but cost them their lives. Should you find yourself in a position where you wish to act to confine the agent, consider covering the agent with something ready to hand that is relatively absorbent and/or vapor resistant, such as a blanket or rain coat, so that you do not come into direct contact with the agent, and do not linger after you have done so.
- The agent will be at least partly confined inside the structure.- if you can't get out directly and have choices, moving up (without passing through the cloud) and putting closed doors between you and the release point are usually good options.
In a Building
- While few buildings are airtight, exchange of air between the interior and exterior of buildings, especially modern buildings, tends to be slow, and so there will generally be a lag in the build-up of the concentration of an externally released agent inside a building.- Locking doors may produce a better seal, but will block access for rescuers and for others outside.
- Tape, such duct tape, can be used to produce a better seal around doors and windows.
- Try to shelter in a room with a telephone so you can contact assistance.
- Most chemical agents are heavier than air.
- This provides an additional barrier to any agent that does penetrate the building.
Inside a car or other vehicle
- The agent cloud will tend to move with the wind.- Remember the wind may shift - do not stop immediately upwind.
- Most chemical agents are heavier than air.
- The agent cloud will tend to move with the wind.- Remember the wind may shift - do not stop immediately upwind.
- Most chemical agents are heavier than air.
- While few buildings are airtight, exchange of air between the interior and exterior of buildings, especially modern buildings, tends to be slow, and so there will generally be a lag in the build-up of the concentration of an externally released agent inside a building.
- while you may not be able to move faster than the cloud, the further you move from the release point the lower the concentration of agent will become as it is diluted by the air.- If you have to move at an angle to the wind direction, try to move in a direction that will take you toward the nearest edge of the cloud.
- If you don't know where the cloud edge is, pick a direction and always move in the same direction (if possible) anytime you must move at an angle to the wind direction.
- Be sure you know what direction the wind is moving, as buildings and geography may interact with the winds to produce localized air movements. Knowing the actual wind direction is important for determining isolation distances and evacuation routes.
- Chemical agents may travel upwind for short distances along building walls as a result of eddies.- Chemical agent clouds will tend to travel down streets oriented parallel to the wind direction, but they will also be channeled along side streets, where they may move at right angles to the wind direction or even upwind.
- Under some conditions, buildings may channel the main cloud at an angle to the wind direction for a substantial distance.
- Buildings may create areas (areas of dead air or vortices and eddies) in which substantial concentrations of agent vapors may be collected.
- Most chemical agents are heavier than air.
- recesses can produce dead spaces in which vapors can accumulate
- Most chemical agents are liquids or solids at ambient temperatures, but will also continue to produce hazardous vapors and often will be contact hazards after they have settled out. They will be a more localized hazard, but they will still be a hazard.- Cold temperatures and rain will cause agents to settle more rapidly. Depending on the agent and how hard it is raining, runoff from the rain may also present a hazard (very heavy rain can remove agent effectively; many agents are effectively hydrolyzed when dissolved, although some agents dissolve poorly, and very heavy rain can both dissolve and hydrolyze and rapidly dilute agents - it is a bad idea to count on this, however).
- Don't leave people in buildings once they can be safely evacuated.- Don't assume interiors are safe because the agent outside has blown away.
CLOSING NOTES
Hydrogen cyanide, with a vapor density of 0.94 relative to air, is an important exception to the general statement that most chemical agents are heavier than air. Its vapor density is sufficiently close to that of air, however, that other factors - convection, wind currents, etc.- will usually be more important in estimating where a cloud will travel.
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Cloud Movement
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