; or (v) as part of a Federal agency-wide, facility-wide, or partial facility-wide lockdown, only if a head of a facility or agency has determined such lockdown is necessary to deescalate an emergency that involves several incarcerated persons and poses a specific and significant risk of imminent serious physical injury to the staff or incarcerated persons, only when there are no less restrictive means to address an emergency, as a last resort after exhausting less restrictive measures, confined to as narrow an area as possible and to as limited number of people as possible, reviewed every hour by the head of the facility or agency, with notification provided to the agency regional or field office, or equivalent office responsible for oversight of the facility, beginning at the time the lockdown reaches 2 hours, and lifted as quickly as possible, not to exceed 4 hours total from the start of the lockdown, 4 hours total in any 24-hour period, or 12 hours total in any 7-day period. (C) Deescalation For placements pursuant to subparagraph (B)(iv), facility staff shall meet with the person at least once an hour to attempt deescalation, work toward their release from such confinement, and determine whether it is necessary to continue to hold the person in such confinement, and for all placements pursuant to subparagraphs (B)(iv) and (B)(v), health care staff must conduct a thorough medical, mental health, social, and behavioral assessment upon admission to such placement, conduct meaningful check-ins every 15 minutes to engage with the person in custody, evaluate and treat any urgent health needs, and attempt any deescalation. If health care staff determines the person should be removed from such confinement for assessment or treatment purposes, or because of a negative impact of such confinement, the person shall be removed to an appropriate setting as determined by health care staff. (D) Prohibition on involuntary confinement No person may be involuntarily confined in their cell under subparagraph (B)(iv) who— (i)