Shelter-in-place

The American Red Cross says the warning is issued when "chemical, biological, or radiological contaminants may be released accidentally or intentionally into the environment" and residents should "select a small, interior room, with no or few windows, taking refuge there.

"[1] Shelter in place in radiological and chemical defense scenarios entails closing all household doors, windows, and vents and taking immediate shelter in a readily accessible location that puts as much indoor air and radiation shielding-mass between the individual and the hazardous outside air, such as a basement or centrally located medium to small room, and trying to make it as airtight as possible by shutting off all ventilation/HVAC systems and extensively sealing the shelter's doors and windows from all outside air contaminants with damp towels, or if available, plastic sheeting and adhesive tape.

[2] Diagrams of what sheltering in place entails following a chemical, biological, radiological or nuclear (CBRN) threat, and how long it is advised to be done for, is provided by the U.S. Federal Emergency Management Agency-affiliated website Ready.gov.

Shelter-in-place over extended periods in epidemics may involve significant logistical considerations including measures to safely provide food, medication and other supplies over time as well as arrangements for social and psychological support.

[20] Governor Andrew Cuomo of New York criticized anyone using the term "shelter in place" for his stay-at-home order as it would invoke panic due to its association with active shooting situations or nuclear wars.

In the United States, facilities like nuclear power plants are required to be equipped with audio alert systems that can be heard within a 10-mile (16 km) radius.

[2] Once a shelter in place is called, residents are expected to immediately go indoors, bring all children and animals with them, and to close and lock windows and doors.