The Evolution of the Vault
By the 1920s, most banks avoided using safes and instead installed gigantic, heavy vaults with walls and doors several feet thick. Vault installations were meant to act as safeguards against robbers, angry mobs and natural disasters. Despite the new security measures, these vaults were still vulnerable to yet another new invention, the cutting torch. Burning oxygen and acetylene gas at about 6,000°F (3,315°C), the torch could easily cut through steel. It was in use as early as 1907, but became wide spread with World War I. Robbers used cutting torches in over 200 bank robberies in 1924 alone. Manufacturers learned to sandwich a copper alloy into vault doors. If heated, the copper alloy melted and flowed. As soon as the burglar removed the heat, the copper re-solidified, sealing the hole. After this design improvement, bank burglaries fell off and were far less common at the end of the 1920s than at the beginning of the decade.