Should you evacuate or shelter after a nuclear blast?
Shelter first. Federal guidance says to get inside the nearest sturdy building, stay there for at least 24 hours, and leave only when officials tell you to or your building is on fire or collapsing.
Driving away feels like the safe choice, but in the first hours it usually is not. FEMA’s planning guidance calls sheltering “one of the most, if not the most, important protective action” people can take in the first few hours after a nuclear explosion, because it protects against blast, heat, radiation, fallout, and smoke (FEMA Planning Guidance, ch. 3). The rest of this page covers when that default changes.
Why officials say shelter first
Fallout is most dangerous in the first hours. FEMA says fallout gives off over half of its energy in the first hour and then keeps decaying quickly, which is why sheltering during the first few hours, up to 24, is a critical protective measure (FEMA Planning Guidance, sec. 1.5). It also warns that in those first hours, lethal radiation levels may be present even tens of miles from ground zero, including where fallout is not visible (sec. 3.3).
A car gives you little protection. FEMA states that “cars and other vehicles are not adequate shelters because they lack dense shielding material” (FEMA Planning Guidance, sec. 3.2). A person stuck in traffic during the first hours is exposed in a way a person in a basement is not.
Sheltering also keeps roads open. FEMA says sheltering “reduces the strain on response organizations and transportation infrastructure” so responders can reach the incident and carry out the evacuations that are critical (ch. 3), and that self-evacuees “may clog transportation arteries, hindering the overall response” (FEMA Planning Guidance, sec. 3.6).
The default: get inside, stay inside, stay tuned
After a detonation, federal planning guidance tells officials to instruct everyone within 50 miles to get inside the nearest building that is not threatened by fire or collapse, stay there, and tune in for more information (FEMA 72-Hour Guidance, Tactic 1).
- Get inside. Brick or concrete multi-story buildings and basements are best, but CDC says “being inside any building is safer than being outside” (CDC, Get Inside). Go to the basement or the middle of the building, away from the walls and roof.
- Stay inside. Ready.gov says sheltering usually lasts at least 24 hours (Ready.gov). CDC says staying inside for at least 24 hours can protect your household until it is safe to leave the area (CDC, Stay Inside).
- Stay tuned. Follow instructions from emergency officials. Ready.gov advises having several ways to receive emergency alerts (Ready.gov).
Do not go out to collect family members. CDC says: “Stay where you are! Going outside to get loved ones could expose you and them to dangerous levels of radiation” (CDC, Get Inside). Agree on this with your household now, so no one is tempted to drive across town.
When to leave your shelter right away
FEMA’s guidance gives priority to immediate threats over longer-term ones. Its example: “even in the DRZ people should leave a burning building,” because the risk of delayed radiation effects is lower than the risk of dying in a fire (FEMA Planning Guidance, ch. 3). (The DRZ, or dangerous radiation zone, is FEMA’s term for the area with the highest fallout levels.)
The template alerts FEMA wrote for officials say the same thing in plain terms: stay inside “unless officials provide other instructions, or your building is threatened by fire or collapse” (FEMA 72-Hour Guidance, Table 2). FEMA’s guidance also names medical emergencies among the reasons a shelter may become unsafe.
If your shelter is poor
Not every building protects well. FEMA says vehicles and single-story wood frame houses without basements “provide limited shielding and should not be considered adequate shelter,” while houses with basements, large multi-story buildings, parking garages, and tunnels can generally cut fallout doses by a factor of 10 or more (FEMA Planning Guidance, sec. 3.2).
FEMA gives specific timing for moving from a poor shelter to a better one nearby:
- Near the detonation, there will be 10 minutes or more before fallout arrives, enough time to find adequate protection (FEMA Planning Guidance, ch. 2). In many areas farther away, FEMA says fallout will arrive an hour or more after the detonation.
- When an adequate shelter is within 15 minutes of travel, people in a poor shelter should stay there no longer than 30 minutes after the detonation before moving (FEMA Planning Guidance, sec. 3.3).
- People in a somewhat better shelter should stay for an hour or two before moving to a nearby adequate shelter.
That move is a short walk or drive to a stronger building, not an evacuation. FEMA’s own example is moving from a single-family home to a commercial building such as a hotel. Ideally you move away from ground zero.
If you get a warning before a detonation
FEMA notes that a ballistic missile attack may leave officials only 15 to 30 minutes between warning and detonation (FEMA 72-Hour Guidance, Tactic 1). That is not enough time to drive out of a metro area. The template warning tells people to get inside a basement or central room of a sturdy building now and stay away from windows and doors. Ready.gov adds that if you are outside when a detonation happens, lie face down to protect exposed skin from heat and flying debris, then go inside the nearest building once the shockwave has passed (Ready.gov).
When and how evacuation happens
Sheltering is short term. FEMA says initial sheltering should be followed by staged, facilitated evacuation for people in fallout-affected areas, and that evacuations “should occur only after appropriate paths have been identified and cleared” (FEMA Planning Guidance, sec. 3.5). Unless there is a fire or another immediate threat, FEMA says no evacuation should be attempted until basic information on where the fallout went is available.
What that means for your household:
- Wait for the instruction. Ready.gov: “If advised to evacuate, listen for information about routes, shelters, and procedures” (Ready.gov). In the most contaminated areas, FEMA’s guidance tells officials to prepare people to evacuate in 12 to 24 hours, once radiation levels drop (FEMA 72-Hour Guidance, Table 6).
- Expect a direction, not just an order. FEMA says officials can often reduce the dose people receive with lateral evacuation, traveling at right angles to the fallout path and away from its centerline (FEMA Planning Guidance, sec. 3.5). Driving straight away from the blast can mean driving along the fallout path.
- You may not need to evacuate at all. FEMA lists people outside the dangerous radiation zone who have even minimally protective shelter, including single-story houses without basements, as a low priority for evacuation, and says officials may simply lift the shelter order for areas clearly outside the hazard zones.
- Do not return early. Ready.gov: if you have evacuated, do not return until local authorities say it is safe (Ready.gov).
Officials give early evacuation priority to people in immediately life-threatening situations, such as fire, structural collapse, or urgent medical needs, and to people sheltering in poor buildings in the most contaminated areas (FEMA Planning Guidance, ch. 3 and sec. 3.5). If someone in your household depends on medical equipment or regular medication, that is part of what you tell officials when you are able to reach them.
The decision, in order
First minutes
First hour
First 24 hours and after
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Next steps
- What to do hour by hour: The first 72 hours
- Where in your building to shelter, and for how long: Shelter in place
- Plan the routes you would use when officials do call an evacuation: Evacuation route planning
- How far you live from publicly documented likely targets: Nuclear targets near me
Gear for this guide
- Go bag list for evacuation What to pack in a go-bag you can carry if officials tell you to evacuate, based on Ready.gov's kit list, with a printable checklist.
- Fallout shelter supplies checklist The supplies to keep where you would shelter from fallout, sized to Ready.gov's kit list, with a printable checklist.