Albert Barnes Commentary Acts 27:34

"Wherefore I beseech you to take some food: for this is for your safety: for there shall not a hair perish from the head of any of you." — Acts 27:34 (ASV)

Not an hair fall from the head, This is a proverbial expression, denoting that they should be preserved safe; that none of them should be lost; and that in their persons they should not experience the least damage (1 Samuel 14:45; 1 Kings 1:52).