Each bulkhead could be sealed by watertight doors. The engine rooms and boiler rooms on the tank top deck had vertically closing doors that could be controlled remotely from the bridge, lowered automatically by a float if water was present, or closed manually by the crew. These took about 30 seconds to close; warning bells and alternative escape routes were provided so that the crew would not be trapped by the doors. Above the tank top level, on the Orlop Deck, F Deck and E Deck, the doors closed horizontally and were manually operated. They could be closed at the door itself or from the deck above.