Chemical weapons are categorized as nerve, blood, blister and incapacitating agents. No matter what the agent is or its concentration, evacuation from the area of attack is always advisable unless you are properly equipped with an appropriate breathing device and protective clothing or have access to collective protection.

Possible signs of chemical threat:

• Many people suffering from watery eyes, twitching, choking, difficulty breathing or losing coordination
• Many sick or dead birds, fish or small animals
• Sprays, vapors or droplets of oily film on surfaces Low-lying clouds, dust, suspended, possibly colored, particles or fog unrelated to the weather

If you see signs of chemical attack:

• Take immediate action to protect yourself and report this incident
• Quickly try to define the impacted area or where the chemical is coming from
• Do not attempt to enter the area without proper training or equipment
• If the chemical is inside the building where you are, get out of the building without passing through the contaminated area, if possible
• If outside, attempt to move upwind of the chemical plume
• If in a car, shut off outside air intake vents and roll up windows if no gas has entered vehicle
  

From the Anti-Terrorism Handbook, California Office of Homeland Security