Federal government emergency management authorities would probably counsel people to shelter-in-place if there was a terrorist act such as a chemical attack.
The reason behind remaining put and locating protection where you happen to be will be based upon whether the chemical is anticipated to dissipate quickly, there isn't time for you to evacuate, or chemical toxins could quickly overtake you unless you find protection immediately.
Always keep a written backup of your prescription medications and orders for professional medical products and supplies with you, a record of all prescription drugs, products and items you use (as well as over-the-counter OTC) as well as an electronic backup on a flash drive, even if you're not computer literate.
Further, remember that after a severe disaster, your prescription drugs or consumable healthcare products may not be easily obtained; therefore, talk to your doctor about creating an emergency medical supply. You should also call and discuss your emergency medical plan with your current insurance company to aid you in acquiring and having enough prescription medication and supplies in reserve just in case you have to stay in an emergency shelter unexpectedly or, for an extended period of time.
If you have the ability to acquire an emergency supply, be certain to set up a system for rotating your supply so it is always up-to-date. If however, you are not able to acquire an emergency supply, be certain to always fill prescription medications on the first day available to get your refill, not the last day.