When a chemical agent is released, the correct response is immediate movement away from the source. Unlike nuclear events where shelter-in-place is typically the primary response, chemical attacks require rapid evacuation in most circumstances. Getting distance from the release point — in the right direction — is the most protective action available.
The Core Rule: Move Upwind
Most chemical agents are denser than air. They flow along the ground and move downwind. Moving upwind takes you against the agent's direction of travel — away from the concentration zone.
Determine wind direction:
- Feel which direction the wind is coming from on your face
- Observe movement of trees, flags, or smoke
- In many coastal and urban environments, daytime breezes are predictable (sea breeze, building corridor effects)
Move in the direction the wind is coming from — not the direction it is going.
⚠️ If wind direction is unknown or changing, move away from the apparent source of the release and towards higher ground. Most dense chemical agents settle in low areas — ravines, underpasses, basements.
Direction and Distance
Lateral and Upwind
Moving perpendicular to the wind direction (laterally) and then upwind takes you out of the contamination plume most quickly. The plume is directional — you can exit it by moving sideways as well as upwind.
Elevated Ground
Agents denser than air (chlorine, VX, some blister agents) concentrate in low areas. Moving to higher ground reduces your concentration exposure.
Away From Enclosed Spaces
Avoid sheltering in underpasses, subway stations, basements, or low-lying enclosed areas during an outdoor chemical release — these spaces trap dense agents and may have higher concentrations than the open air.
What to Do While Moving
- Cover your respiratory system — improvised mask, N95 respirator, or a held cloth if nothing else is available.
- Cover exposed skin — pull sleeves down, wrap scarves around the neck, use any available barrier.
- Move at a steady, deliberate pace — running increases breathing rate and therefore inhalation dose. Brisk walking while protecting your airway is better than sprinting while gasping.
- Do not stop to help others until you are clear of the plume — otherwise you become a secondary casualty.
- Avoid touching surfaces in the contaminated area — contaminated ground, vehicles, and structures transfer agent to hands and clothing.
When to Shelter in Place Instead
Shelter-in-place is preferable when:
- The chemical cloud has already passed your location and you are not in it
- Outdoor movement would require passing through a higher-concentration area
- The release is outdoors and you are in a well-sealed indoor space upwind
- Official guidance specifically instructs shelter-in-place
If sheltering:
- Move to an interior room on an upper floor (for dense agents) or any interior room with few openings.
- Close and seal all windows, doors, and ventilation openings.
- Turn off air conditioning and heating systems.
- Improvised sealing with wet towels at door bases and tape at window gaps.
- Monitor official broadcasts for when it is safe to exit.
After Evacuating From the Plume
Once you are clear of the immediate contamination:
1. Decontaminate Before Entering Buildings
If you passed through contaminated air or touched contaminated surfaces:
- Remove outer clothing — this removes 80% of contamination. Bag it; do not carry it with you.
- Flush exposed skin and eyes with large amounts of clean water.
- Do not enter vehicles, homes, or public buildings until you have removed outer clothing.
- Contaminated clothing brought inside transfers agent to indoor surfaces.
2. Report Your Location to Emergency Services
Call emergency services and:
- Give your location
- Describe your symptoms
- State which direction you came from
- Describe what you observed (smell, casualties, visible cloud or liquid)
This information helps emergency responders map the affected area and direct others.
3. Do Not Return to the Area
Even after visible clouds have dispersed:
- Persistent agents (VX, mustard) remain on surfaces for hours to days
- Liquids that appear to be water may be dissolved agents
- Official decontamination and clearance is required before the area is safe
Special Situations
In a Vehicle
If you are in a vehicle near a chemical release:
- Drive away — upwind if possible, or out of the area by any available route.
- Close all windows and vents; turn off ventilation.
- Do not stop to check on casualties in the contaminated area.
- Drive until you have clearly cleared the area, then stop and follow standard decontamination steps.
In a Building in the Plume Path
If a cloud is moving toward your building:
- Assess: is evacuating now going to take you through the plume, or away from it?
- If away from it — evacuate immediately.
- If through it — shelter in place, seal the room, monitor.
- If the building is already contaminated — the priority becomes getting to fresh air outside the contaminated zone as quickly as possible.
Quick Reference
| Action | Detail |
|---|
| Primary response | Move upwind and to higher ground immediately |
| While moving | Cover airway; cover skin; brisk walk, not sprint |
| Dense agents | Avoid low areas; move to elevation |
| Shelter instead if | Already past you; moving would go through higher concentration |
| Shelter steps | Seal all openings; turn off ventilation; upper floor or interior |
| After evacuating | Remove outer clothing; flush skin/eyes; report to emergency services |
| Do not return | Until official clearance — persistent agents remain on surfaces |