The disaster involving the MS Herald of Free Enterprise on March 6, 1987, resulted in the loss of 193 lives. The ferry capsized just minutes after leaving the port of Zeebrugge because the bow doors had been left open, allowing water to flood the car deck—a phenomenon known as the "Free Surface Effect" which destroyed the ship's stability instantly. Most of the victims died of hypothermia in the freezing North Sea waters rather than drowning. It remains one of the deadliest maritime disasters involving a British ship in peacetime. The subsequent investigation revealed a "culture of complacency" within the company, Townsend Thoresen, as it was discovered that the assistant boatswain was asleep in his cabin instead of closing the doors. This tragedy led to massive international changes in maritime safety regulations, including the mandatory installation of sensors and television monitors to ensure that all hull openings are closed and secured before a vessel leaves the berth.