Should I purchase a gas mask as protection?
No. A mask would only protect you if you were wearing it when a chemical attack occurs. A release of a chemical agent is most likely to be done without anyone knowing it ahead of time. Masks that are not properly fitted will NOT give you adequate protection. Protective masks do not fit small children. There are reports of accidental suffocation when people have worn masks incorrectly.

Should I keep a stockpile of water?
You can live only a few days without water, so it is very important that you create an emergency supply of safe water. One gallon of safe water per person per day is the bare minimum for survival. Most surplus stores can sell you inexpensive, 50-gallon plastic drums. Properly chlorinated tap water can be safely stored for up to three months. Water purification tablets are also readily available from many surplus and camping supply stores.

What are the signs of a chemical attack?
Many chemical agents cannot be seen or smelled. Observe the following rule of thumb: If a single person is on the ground, choking or seizing, this individual is probably having a heart attack or some type of seizure. However, if several people are down, coughing, vomiting, or seizing, they could be reacting to the presence of a toxic substance. Leave the area immediately, call 911, and tell the dispatcher a hazardous gas may be present.

What should I do during a chemical attack?

If the attack occurs indoors:

Exit the building immediately. Avoid puddles of liquid. Once outside, if you were directly exposed to a toxic substance, discarding your modesty and shedding your clothes could save your life. Taking off your outer clothing can remove roughly 80 percent of the contamination hazard. Look for a nearby fountain, pool, or other source of water to quickly and thoroughly rinse any skin that may have been exposed (e.g., jump in a pool). Water alone is an effective decontaminant. Try to remain calm. 

If the attack occurs outdoors:
Birds and other small animals would very quickly be overcome by a poison gas, so if birds and insects are dropping from the sky, this is an indication of a possible chemical attack. The most important thing is to get a physical barrier between you and the toxic cloud. Get indoors quickly, into a building or a car. Shut all windows and doors and turn off the air conditioner or heater. Plug any air drafts around doors or windows. Call 911 and notify authorities that a hazardous gas may be present. The wind will carry the toxic hazard away within a relatively short period of time. Stay indoors, and turn on the television or radio for news. Authorities will notify you when it is safe to go outside. If you are at home, put your clothes in a plastic bag and take a shower to remove any contamination to which you may have been exposed.