How do you shelter in place during a chemical release?

Short answer. When told to shelter in place for a chemical release, go indoors, close and lock windows and doors, turn off fans, air conditioning and the furnace, and seal a room on the highest floor possible with few or no windows ¹. Stay there until officials give the "all clear" ¹. The EPA says this is most likely no more than a few hours ³.

When is sheltering in place the right call?

Authorities can ask you to evacuate, to shelter in place, or to protect your breathing ³. The EPA describes sheltering in place as "a good action to take if there is a short release or small amount of hazardous material in the air" ³. It also notes that studies show "even poorly sealed buildings give some protection," and that "staying inside is safer than trying to outrun a release" ³.

The decision is not yours to guess: follow the instruction in the official alert. Emergency services work out which area may be affected, using modelling and monitoring, and give information about what happened ⁵. If you are told to evacuate, leave; if you are told to stay, stay.

A real case shows why the instruction matters. In April 2019, at least 500 gallons (1,893 L) of anhydrous ammonia leaked from two tanks towed by a farm tractor in Lake County, Illinois ⁸. Residents within a 1-mile radius were ordered to shelter in place and told by reverse 9-1-1 to remain indoors, close all doors and windows and shut off heating, ventilation and air conditioning ⁸. Of 48 residents surveyed, 33 (69%) stayed home until the order was lifted ⁸. In total, 83 people were evaluated at six hospitals, 14 were hospitalized and no one died ⁸.

What are the steps, in order?

1. Get inside a solid building now. If you are outdoors, go into a building, but not the building where the release happened ⁵. Cars and other vehicles may not be airtight enough to protect you ¹; the UK government says vehicles and tents do not give sufficient protection ⁵.
2. Close and lock all exterior doors and windows ¹². Close vents and the fireplace damper ¹². The UK government adds trickle vents in window frames ⁵.
3. Turn off anything that pulls outside air in: fans, air conditioners and the furnace ¹. Ready.gov also gives the option of setting ventilation systems to 100 percent recirculation so that no outside air is drawn into the building ².
4. Go to your shelter room (see the next section) with your phone and charger ¹.
5. Seal the room. Tape around the door, cover windows with plastic sheeting, and tape over vents, window air conditioners, bathroom and kitchen exhaust fans, and stove and dryer vents ¹². The CDC suggests pre-cutting plastic sheets 2 to 4 mil thick to fit your windows ¹. With no plastic on hand, push towels, sheets or clothing into vents and under the door ¹.
6. Stay informed. Follow radio, TV, mobile alerts or a news app ¹. Contact someone outside the area to say where you are and that you are safe ¹.
7. If gas or vapors may have entered, take shallow breaths through a cloth or towel ²; the EPA says a wet cloth over the nose and mouth "will act as a filter and offer some protection" ³. Avoid food or water that may be contaminated ².
8. Do not go outside, even to help others, until authorities say it is safe ².

Which room should you choose?

The CDC asks for a room that you can seal off, that is large, that has a water source, that has no or few windows, that is as far as possible from the outside, and that sits on the highest floor possible ¹. Ready.gov says to identify an above-ground shelter room with as few openings as possible ².

A basement does not fit these criteria: US chemical guidance points to above-ground rooms, on the highest floor possible ¹². Plan the room before an emergency, with tape, scissors, towels and pre-cut plastic stored nearby ¹.

How is this different from sheltering from radiation?

The two instructions sound the same ("go inside, stay inside") but the best room is opposite.

For radiation, Ready.gov says to "remain in the most protective location (basement or center of a large building) for the first 24 hours" ⁴. There, the aim is to "put as many walls between you and the outside" as possible, and radiation levels drop rapidly during the first 24 hours ⁴. For a chemical release, the aim is to keep outside air out of the room, which is why US chemical guidance calls for a sealed room on the highest floor possible ¹². If an alert does not say which hazard it is, follow its wording exactly.

What do official alerts mean?

In the United States, Wireless Emergency Alerts come in five types: National Alerts, Imminent Threat Alerts, Public Safety Alerts, AMBER Alerts and opt-in test messages ⁶. National Alerts are "only sent during a national emergency" ⁶. Imminent Threat Alerts cover current or emerging threats such as natural or human-made disasters and extreme weather, and Public Safety Alerts are "less severe than imminent threat alerts" ⁶. Each alert shows its type, time, required action and issuing agency; FEMA's advice is to follow the action it recommends ⁶. Messages can be up to 360 characters on phones and networks that support it, and alerting authorities must also include a 90-character version ⁶.

On radio and TV, the Emergency Alert System uses event codes defined in federal rules; the ones linked to this topic are optional state and local codes ⁷:

The code only names the event ⁷; listen to the full broadcast for the action to take.

What official agencies recommend

• CDC (United States): seal a large room with water, few windows, on the highest floor possible; turn off fan, air conditioner and furnace; tape the door and cover windows with 2-4 mil plastic; wait for the "all clear" ¹.
• Ready.gov / FEMA (United States): above-ground shelter room with few openings; seal with duct tape and plastic sheeting; turn off ventilation or set it to 100 percent recirculation; do not go outside until authorities say it is safe ².
• EPA (United States): shelter for short or small releases; close doors and windows; turn off heating, cooling and ventilation; do not use fireplaces; most likely no more than a few hours ³.
• UK Government: "Go in, stay in, tune in"; close doors, windows and vents, including trickle vents; turn off equipment that brings outside air in; sheltering "may be required for a number of hours depending on the circumstances" ⁵. If you were caught outside, removing outer clothing "can remove around 90% of the contamination" ⁵.

Where they differ: the CDC and Ready.gov tell households to seal a room with plastic and tape ¹², while the UK page focuses on closing openings and switching off ventilation, without plastic sheeting ⁵. On vehicles, the CDC and the UK say they may not protect you ¹⁵, while the EPA lists getting into your car as an option if you are caught outside ³. On duration, the EPA expects a few hours ³, the CDC warns it could stretch to a few days or longer ¹, and the UK gives no fixed figure ⁵.

Frequently asked questions

Should I go to the basement during a chemical spill?

No. US guidance calls for an above-ground room, on the highest floor possible ¹². The basement is the advice for radiation, not chemicals ⁴.

Can I shelter in my car?

A building is better. The CDC warns that vehicles may not be airtight enough and tells people outside to find a shelter instead ¹, and the UK says vehicles do not provide sufficient protection ⁵. The EPA mentions getting into your car if you are outside, with windows closed and outside ventilation off ³.

How long will I have to stay inside?

Most likely no more than a few hours, according to the EPA ³, but the CDC says it may be a few hours, possibly a few days, or longer ¹. Stay until police, fire or local officials give the "all clear" ¹.

What do I do when the order is lifted?

Follow local officials' guidance when going outside ¹. If you may have been exposed, go to a medical facility for screening as soon as it is safe ².

Should I pick my children up from school?

Do not go outside during the order, even to help others ². Call or text to check in and follow the instructions officials give for your area ¹².

Make your household plan before you need it

Choosing the room, storing tape and pre-cut plastic, and agreeing on who contacts whom are decisions to make before an alert ¹. The Phaenyx personal plan helps you write those decisions down for your home and your country's official guidance. Build your Phaenyx plan.

Sources

1. U.S. Centers for Disease Control and Prevention (CDC) — What to Do to Shelter in Place for a Chemical Emergency — https://www.cdc.gov/chemical-emergencies/response/shelter-in-place.html (accessed 2026-10-20)
2. Ready.gov (FEMA) — Chemicals and Hazardous Materials Incidents — https://www.ready.gov/chemicals (accessed 2026-10-20)
3. U.S. Environmental Protection Agency (EPA) — Appendix L: What to Do in a Chemical Emergency — https://www.epa.gov/system/files/documents/2022-01/appendix-l-what-to-do-in-a-chemical-emergency.pdf (accessed 2026-10-20)
4. Ready.gov (FEMA) — Radiation Emergencies — https://www.ready.gov/radiation (accessed 2026-10-20)
5. UK Government (GOV.UK) — What to do in a chemical emergency — https://www.gov.uk/government/publications/chemical-emergencies-information-for-the-public/what-to-do-in-a-chemical-emergency (accessed 2026-10-20)
6. Federal Emergency Management Agency (FEMA) — Wireless Emergency Alerts — https://www.fema.gov/emergency-managers/practitioners/integrated-public-alert-warning-system/public/wireless-emergency-alerts (accessed 2026-10-20)
7. U.S. Code of Federal Regulations, via Cornell LII — 47 CFR § 11.31 EAS protocol — https://www.law.cornell.edu/cfr/text/47/11.31 (accessed 2026-10-20)
8. CDC MMWR — Anhydrous Ammonia Chemical Release — Lake County, Illinois, April 2019 (2020;69(4):109-113) — https://pmc.ncbi.nlm.nih.gov/articles/PMC7004403/ (accessed 2026-10-20)