The 25th percentile New SAT score is 1450, and the 75th percentile SAT score is 1570. In other words, a 1450 places you below average, while a 1570 will move you up to above average. There's no absolute SAT requirement at Duke, but they really want to see at least a 1450 to have a chance at being considered.
It is a safety procedure in industries that lock dangerous machines and ensure that there is no operation until maintenance or repairs have been made.