A chemical threat is fear of a release of poisonous vapors, aerosols, liquids, and solids being dispensed into the air or water ways which would have a toxic effect on people, animals, and/or plants.
Chemical agent or chemical poisons are primarily used in war, terrorism and riot control. These kinds of chemical threats are very real and are often dispensed through bombs or via some type of projectile. They can also be sprayed from aircraft, boats, and vehicles or shot out of some type of weapon.
Several things you should keep in mind about chemical threats:
Chemical warfare agents are substances intended for use in military operations to kill, seriously injure or incapacitate people because of its physiological effects. Excluded from this definition are riot control agents, herbicides, smoke, and flame.
Top 3 agents used for chemical terrorism:
The nerve agents are a group of particularly toxic chemical warfare agents. They were developed just before and during World War II and are related chemically to the organophosphorus insecticides. The principle agents in this group are tabun, sarin and methylphosphonothioic acid.
Blister or Vesicant Agents
Blister or vesicant agents are likely to be used both to produce casualties and to force opposing troops to wear full protective equipment thus degrading fighting efficiency, rather than to kill, although exposure to such agents can be fatal. Blister agents can be thickened in order to contaminate terrain, ships, aircraft, vehicles or equipment with a persistent hazard.
Vesicants burn and blister the skin or any other part of the body they contact. They act on the eyes, mucous membranes, lungs, skin and blood-forming organs. They damage the respiratory tract when inhaled and cause vomiting and diarrhea when ingested. Types of vesicant agents are sulfur mustard and nitrogen mustard.
"Chemical agents which attack lung tissue, primarily causing pulmonary edema, are classed as lung damaging agents", according to the Federation of American Scientists.(http://www.fas.org/programs/bio/chemweapons/cwagents.html#b04) On that page, they state that the types of choking agents are phosgene, diphosgene, chloropicrin and chlorine.
Depending upon the type of chemical, it can either have an immediate effect (seconds to minutes) or a delayed effect (2-48 hours).
Signs of a chemical release include people having difficulty breathing, experiencing eye irritation, losing coordination, becoming nauseated, or having a burning sensation in the nose, throat, and lungs.
Also, the presence of many dead insects or birds may indicate a chemical agent release.
In most cases, the authorities will ask you to shelter-in-place if a suspected chemical threat is imminent. When this happens, you will be asked to remain in your home or office. To be safe, you need to do the following immediately:
To minimize health issues, a person must be decontaminated within minutes of exposure to a chemical agent. Until told to do so by the authorities, stay inside where it is safe. Even if it appears that others need help, do not go outside the safety of a facility or place of shelter.
Anyone who has been affected by any kind of chemical must seek professional medical help. If it is not possible to get to a medical professional immediately, read the procedures below to learn how to decontaminate yourself. It is critical that this be done as soon as possible. If anyone else has been exposed to a chemical threat or directly come in contact with a chemical, they should follow the same procedure or you should help them if you can.
Federation of American Scientists - Types of Chemical Weapons
FEMA - Chemical Attacks