I work night shifts and it's largely admitted that those who wants to sleep can do so during their break time. Our chief-nurse has even bought two Lay-Z-Boys for our staff room, paid with money from the budget unit. We also take unoccupied stretchers (we don't use them at night) or beds, in unoccupied rooms to take a nap. Napping during night shifts is sometimes essential to stay alert 'til morning!!