Bank vault

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This large 24-bolt Diebold vault door at the Winona National Bank was built in the early 1900s. On the right is the back side of the open door. To the right of the door's center are two linked boxes for the combination mechanisms and to the left is a four-movement time lock. This door has a four-point system for pressing the door into its opening (note the two stanchions left of the door opening) capable of exerting one third of the door's weight in closing force. Since this door weighs 22.5 short tons (20.4 t) this system is capable of applying 7.5 short tons-force (67 kN) inward.

A bank vault is a secure space where money, valuables, records, and documents are stored. It is intended to protect their contents from theft, unauthorized use, fire, natural disasters, and other threats, much like a safe. Unlike safes, vaults are an integral part of the building within which they are built, using armored walls and a tightly fashioned door closed with a complex lock.

Historically, strongrooms were built in the basements of banks where the ceilings were vaulted, hence the name. Modern bank vaults typically contain many safe deposit boxes, as well as places for teller cash drawers and other valuable assets of the bank or its customers. They are also common in other buildings where valuables are kept such as post offices, grand hotels, rare book libraries and certain government ministries.

Vault technology developed in a type of arms race with bank robbers. As burglars came up with new ways to break into vaults, vault makers found new ways to foil them. Modern vaults may be armed with a wide array of alarms and anti-theft devices. Some 19th and early 20th century vaults were built so well that today they are difficult to destroy, even with specialized demolition equipment.[1] These older vaults were typically made with steel-reinforced concrete. The walls were usually at least 1 ft (0.3 m) thick, and the door itself was typically 3.5 ft (1.1 m) thick. Total weight ran into the hundreds of tons (see the Federal Reserve Bank of Cleveland). Today vaults are made with thinner, lighter materials that, while still secure, are easier to dismantle than their earlier counterparts.


J&J Taylor Strongroom from 1901
Emergency vault door and combination locks at the Portuguese National Bank Museum in Lisbon. Vault door built by the York Safe and Lock Company, Pennsylvania, United States
Vault lock and two keys from the National German American Bank in Saint Paul, Minnesota, 1856

The need for secure storage stretches far back in time. The earliest known locks were made by the Egyptians. Ancient Romans used a more sophisticated locking system, called warded locks. Warded locks had special notches and grooves that made picking them more difficult. Lock technology advanced independently in ancient India, Russia, and China, where the combination lock is thought to have originated. In the United States, most banks relied on small iron safes fitted with a key lock up until the middle of the nineteenth century. After the Gold Rush of 1849, unsuccessful prospectors turned to robbing banks. The prospectors would often break into the bank using a pickaxe and hammer. The safe was usually small enough that the thief could get it out a window, and take it to a secluded spot to break it open.

Banks demanded more protection and safe makers responded by designing larger, heavier safes. Safes with a key lock were still vulnerable through the key hole, and bank robbers soon learned to blast off the door by pouring explosives in this opening. In 1861, inventor Linus Yale Jr. introduced the modern combination lock. Bankers quickly adopted Yale's lock for their safes, but bank robbers came up with several ways to get past the new invention. It was possible to use force to punch the combination lock through the door. Other experienced burglars learned to drill holes into the lock case and use mirrors to view the slots in the combination wheels inside the mechanism. A more direct approach was to simply kidnap the bank manager and force him to reveal the combination.

After the inventions of the combination lock, James Sargent—an employee of Yale—developed the "theft-proof lock". This was a combination lock that worked on a timer. The vault or safe door could only be opened after a set number of hours had passed, thus a kidnapped bank employee could not open the lock in the middle of the night even under force. Time locks became widespread at banks in the 1870s. This reduced the kidnappings, but set bank robbers to work again at prying or blasting open vaults. Thieves developed tools for forcing open a tiny crack between the vault door and frame. As the crack widened, the thieves levered the door open or poured in gunpowder and blasted it off. Vault makers responded with a series of stair-stepped grooves in the door frame so the door could not be levered open. But these grooves proved ideal for a new weapon: liquid nitroglycerin. Professional bank robbers learned to boil dynamite in a kettle of water and skim the nitroglycerin off the top. They could drip this volatile liquid into the door grooves and destroy the door. Vault makers subsequently redesigned their doors so they closed with a thick, smooth, tapered plug. The plug fit so tightly that there was no room for the nitroglycerin.

One King West Hotel & Residence Vault Door Combination Viewer designed by Frederick S. Holmes
Pennsylvania Treasury Cylindrical Vault Door with Combination Viewers

Another attempt to deter robberies was the advent of the combination viewer, designed by Frederick S. Holmes. Vault door combination viewers are steel boxes mounted on door jambs that operate combination locks, locking bolts, pressure systems, and door rotation remotely.  Early 1900s trade publications and patents refer to these complex devices as ‘illuminated dial cases’, ‘periscope attachments’, ‘periscopic sights’, ‘telescopic boxes’, and ‘time lock adjusters’ and are found with all vault door types - circular, rectangular and cylindrical. The combination locks and bolt-throwing mechanism are located inside the vault creating a solid vault door with no spindle holes.  Entry requires two points of attack (door and jamb) which doubles the time required for burglars to breach the vault. Frederick S. Holmes was a prominent bank vault engineer who designed bank vaults throughout the world in the early 1900s.  He specialized in jamb-controlled vaults, many with combination viewers. The largest circular, hinged vault door in the world is at the Federal Reserve Bank of Cleveland which has combination viewers on the main and emergency vault doors. One of the largest cylindrical vault doors in the world is at the Pennsylvania Treasury which has dual combination viewers.

By the 1920s, most banks avoided using safes and instead turned to gigantic, heavy vaults with walls and doors several feet thick. These were meant to withstand not only robbers but also 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 (3,300 °C), the torch could easily cut through steel. It was in use as early as 1907, but became widespread 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 high thermal conductivity of copper dissipates the heat to prevent melting or burning. 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.

Technology continues in the race with bank robbers, coming up with new devices such as heat sensors, motion detectors, and alarms. Bank robbers have in turn developed even more technological tools to find ways around these systems. Although the number of bank robberies has been cut dramatically, they are still attempted.

Materials used in vaults and vault doors have changed as well. The earlier vaults had steel doors, but because these could easily be cut by torches, different materials were tried. Massive cast iron doors had more resistance to acetylene torches than steel. The modern preferred vault door material is the same concrete as used in the vault wall panels. It is usually clad in steel for cosmetic reasons.


Vault of a retail bank under demolition

Bank vaults are built as custom orders. The vault is usually the first aspect of a new bank building to be designed and built. The manufacturing process begins with the design of the vault, and the rest of the bank is built around it. The vault manufacturer consults with the customer to determine factors such as the total vault size, desired shape, and location of the door. After the customer signs off on the design, the manufacturer configures the equipment to make the vault panels and door. The customer usually orders the vault to be delivered and installed. That is, the vault manufacturer not only makes the vault parts, but brings the parts to the construction site and puts them together.

Bank vaults are typically made with steel-reinforced concrete. This material was not substantially different from that used in construction work. It relied on its immense thickness for strength. An ordinary vault from the middle of the 20th century might have been 18 in (45.72 cm) thick and was quite heavy and difficult to remove or remodel around. Modern bank vaults are now typically made of modular concrete panels using a special proprietary blend of concrete and additives for extreme strength. The concrete has been engineered for maximum crush resistance. A panel of this material, though only 3 in (7.62 cm) thick, may be up to 10 times as strong as an 18 in-thick (45.72-cm) panel of regular formula concreted.

There are at least two public examples of vaults withstanding a nuclear blast. The most famous is the Teikoku Bank in Hiroshima whose two Mosler Safe Company vaults survived the atomic blast with all contents intact. The bank manager wrote a congratulatory note to Mosler.[2][3] A second is a vault at the Nevada National Security Site (formerly the Nevada Test Site) in which an above ground Mosler vault was one of many structures specifically constructed to be exposed to an atomic blast in Operation Plumb Bob - Project 30.4:Response of Protective Vaults to Blast Loading.[4][5]

Manufacturing process[edit]


The wall panels are molded first using a special reinforced concrete mix. In addition to the usual cement powder, stone, etc., additional materials such as metal shavings or abrasive materials may be added to resist drilling penetration of the slab. Unlike regular concrete used in construction, the concrete for bank vaults is so thick that it cannot be poured. The consistency of concrete is measured by its "slump". Vault concrete has zero slump. It also sets very quickly, curing in only six to 12 hours, instead of the three to four days needed for most concrete.[6][7]

  • A network of reinforcing steel rods are manually placed into the damp mix.
  • The molds are vibrated for several hours. The vibration settles the material and eliminates air pockets.
  • The edges are smoothed with a trowel, and the concrete is allowed to harden.
  • The panels are removed from the mold and placed on a truck for transport to the customer's construction site.


The vault door is also molded of special concrete used to make the panels, but it can be made in several ways. The door mold differs from the panel molds because there is a hole for the lock and the door will be clad in stainless steel. Some manufacturers use the steel cladding as the mold and pour the concrete directly into it. Other manufacturers use a regular mold and screw the steel on after the panel is dry.

Round vault doors were popular in the early 20th century and are iconic images for a bank's high security. They fell out of favor due to manufacturing complexities, maintenance issues (door sag due to weight) and cost, but a few examples are still available.[8][9]

A day gate is a second door inside the main vault door frame used for limited vault protection while the main door is open. It is often made of open metal mesh or glass and is intended to keep a casual visitor out rather than to provide true security.[10]


A vault door, much like the smaller burglary safe door, is secured with numerous massive metal bolts (cylinders) extending from the door into the surrounding frame. Holding those bolts in place is some sort of lock. The lock is invariably mounted on the inside (behind) of the difficult-to-penetrate door and is usually very modest in size and strength, but very difficult to gain access to from the outside. There are many types of lock mechanisms in use:

  • A combination lock similar in principle to that of a padlock or safe door is very common. This is usually a mechanical device but products incorporating both mechanical and electronic mechanisms are available, making certain safe cracking techniques very difficult.[11]
  • Some high-end vaults employ a two piece key to be used in conjunction with a combination lock. This key consists of a long stem as well as a short stamp which should be safe guarded separately and joined together to open the vault door.[12]
  • A dual control (dual custody) combination lock has two dials controlling two locking mechanisms for the door. They are usually configured so that both locks must be dialed open at the same time for the door to be unlocked. No single person is given both combinations, requiring two people to cooperate to open the door. Some doors may be configured so that either dial will unlock the door, trading off increased convenience for lessened security.
  • A time lock is a clock that prevents the vault's door from opening until a specified number of hours have passed. This is still the "theft proof" lock system that Sargent invented in the late nineteenth century. Such locks are manufactured by only a few companies worldwide. The locking system is supplied to the vault manufacturer preassembled.
  • Many safe-cracking techniques also apply to the locking mechanism of the vault door. They may be complicated by the sheer thickness and strength of the door and panel.


  • The finished vault panels, door, and lock assembly are transported to the bank construction site. The vault manufacturer's workers then place the panels enclosed in steel at the designated spots and weld them together. The vault manufacturer may also supply an alarm system, which is installed at the same time. While older vaults employed various weapons against burglars, such as blasts of steam or tear gas, modern vaults instead use technological countermeasures. They can be wired with a listening device that picks up unusual sounds, or observed with a camera. An alarm is often present to alert local police if the door or lock is tampered with.

US resistance standards[edit]

Quality control for much of the world's vault industry is overseen by Underwriters Laboratories, Inc. (UL), in Northbrook, Illinois. Until 1991, the United States government also regulated the vault industry. The government set minimum standards for the thickness of vault walls, but advances in concrete technology made thickness an arbitrary measure of strength. Thin panels of new materials were far stronger than the thicker, poured concrete walls. Now the effectiveness of the vault is measured by how well it performs against a mock break-in. Manufacturers also do their own testing designing a new product to make sure it is likely to succeed in UL trials.[13] Key points include:

  • It is based on using "common hand tools, picking tools, mechanical or portable electric tools, grinding points carbide drills, pressure applying devices or mechanisms, abrasive cutting wheels, power saws, coring tools, impact tools, fluxing rods, and oxy-fuel gas cutting torches".
  • A breach is a hole in the door or wall of at least 96 square inches (6 × 16 in (15.24 × 40.64 cm)) or breaking locking bolts to allow the door to open.
  • Considers only the time actually spent working (excludes setup, rests, etc.)
  • Does not cover attacks with a thermal lance or explosives.
  • UL-608 makes no claims as to the fire resistance of the vault.
  • Applies to the door and all sides.
  • The lock, ventilation, alarms, etc. are covered by other UL standards.
Rating Time to Breach Vault
Class M 15 minutes
Class I 30 minutes
Class II 60 minutes
Class III 120 minutes

European resistance standards[edit]

As with the US, Europe has agreed a series of test standards to assure a common view of penetrative resistance to forcible attack.[14] The testing regime is covered under the auspices of Euronorm 1143-1:2012 (also known as BS EN 1143-1: 2012),[15] which can be purchased from approved European standards agencies.[16][17]

Key points include:

A modern highly portable core drill
An explosive door breaching test
  • Standard covers burglary resistance tests against free-standing safes and ATMs, as well as strongrooms and doors
  • Tests are undertaken to arrive at a grade (0 to XIII) with two extra resistance qualifiers (one for the use of explosives the other for core drills)
  • Test attack tools fall into five categories with increasing penetrative capability, i.e. Categories A–D and S
  • Penetration success is measured as partial (125mm diameter hole) or full (350mm diameter hole)
  • Considers only the time actually spent working (excludes setup, rests, etc.)
  • EN 1143-1 makes no claims as to the fire resistance of the vault
  • EN 1300 covers high security locks, i.e. four lock classes (A, B, C and D)[18]
  • Applies to the door and all vault sides.
Resistance Grade Resistance Value to Breach Vault Lock Quantity Explosive Rating Possible Core Drill Rating Possible
0 30 One No No
I 50 One No No
II 80 One Yes No
III 120 One Yes No
IV 180 Two Yes No
V 270 Two Yes No
VI 400 Two Yes No
VII 600 Two Yes No
VIII 825 Two Yes Yes
IX 1050 Two Yes Yes
X 1350 Two Yes Yes
XI 2000 Two or Three Yes Yes
XII 3000 Two or Three Yes Yes
XIII 4500 Two or Three Yes Yes


The manufacturing process itself has no unusual waste or byproducts, but getting rid of old bank vaults can be a problem. Newer, modular bank vaults can be moved if a bank closes or relocates. They can also be enlarged if a bank needs to change. Older bank vaults are quite difficult to demolish. If an old bank building is to be renovated for another use, in most cases a specialty contractor has to be called in to demolish the vault. A vault's demolition requires massive wrecking equipment and may take months of work at a large expense. At least one company in the United States refurbishes old vault doors that are then resold.

In some cases, the new owner of a former bank building will opt to use the vault for some alternative purpose.


Bank vault technology changed rapidly in the 1980s and 1990s with the development of improved concrete material. Bank burglaries are also no longer the substantial problem they were in the late 19th century up through the 1930s, but vault makers continue to alter their products to counter new break-in methods.

An issue in the 21st century is the thermal lance. Burning iron rods in pure oxygen ignited by an oxyacetylene torch, it can produce temperatures of 6,600–8,000 °F (3,650–4,430 °C). The thermal lance user bores a series of small holes that can eventually be linked to form a gap. Vault manufacturers work closely with the banking industry and law enforcement in order to keep up with such advances in burglary.


  1. ^ "Demolition crew cracks the old U.S. Bank vault".
  2. ^ "Letters of Note: Your Products are Stronger than the Atomic Bomb". 16 September 2010. Archived from the original on 19 September 2010. Retrieved 16 September 2010.
  3. ^ "Unbreakable: Hiroshima and the Mosler Safe Company". CONELRAD Adjacent. 26 August 2010. Retrieved 26 August 2010.
  4. ^ "A Nuclear Family Vacation". Slate. Slate Magazine. 11 July 2005. Archived from the original on 13 July 2005. Retrieved 11 July 2005.
  5. ^ "Slate's Well-Traveled: A Nuclear Family Vacation". NPR. Retrieved 15 July 2005.
  6. ^ "Discovery Channel (UK) How Do They Do It? (Season 3 / Episode 7 / Part 2) Diebold Vault Construction (YouTube)". YouTube. Retrieved 28 December 2010.[dead YouTube link]
  7. ^ "Hercvlite Vault Panels". Archived from the original on 17 December 2010. Retrieved 28 December 2010.
  8. ^ "Vault Structure Inc. Round Vault Doors". Archived from the original on 11 April 2011. Retrieved 28 December 2010.
  9. ^ "VSI 360 Round Vault Door" (PDF). Archived from the original (PDF) on 11 July 2011. Retrieved 28 December 2010.
  10. ^ "Installation Instructions for Overly GSA Class 5 Vault Door" (PDF). Overly Door Company. Archived from the original (PDF) on 15 July 2011. Retrieved 28 December 2010.
  11. ^ "Kaba-MAS X-09 and CDX-09 High Security Locks" (PDF). December 2010. p. 8.
  12. ^ Scott Selby & Greg Campbell (2010). Flawless: Inside the Largest Diamond Heist in History. Sterling. pp. 148–149.
  13. ^ "UL 608 Burglary Resistant Vault Doors and Modular Panels". Underwriter's Laboratories. Archived from the original on 21 April 2012. Retrieved 30 October 2012.
  14. ^ "Requirements on strongrooms in cast in-situ and/or pre-fabricated construction ECB-S R03" (PDF). ECB-S. Retrieved 4 September 2017.
  15. ^ "Red Book Live, Part 4, Section 2" (PDF). LPCB. Retrieved 4 September 2017.
  16. ^ "BS EN 1143-1:2012 - Secure storage units. Requirements, classification and methods of test for resistance to burglary. Safes, ATM safes,strongroom doors and strongrooms". Retrieved 4 September 2017.
  17. ^ Standards, European. "EN 1143-1". Retrieved 4 September 2017.
  18. ^ "EN 1300 Locks". Retrieved 5 September 2017.
  19. ^ "Trinity Place Bank Vault Bar".
  20. ^ a b Abelson, Jenn (18 September 2009). "A sour ending for sweets shop: Herrell's Harvard Square site closing after 27 years". The Boston Globe.
  21. ^ "Welcome to Vault".
  22. ^ a b c d e f g h "Ten Incredible Repurposed Bank Vaults – RecycleNation".
  23. ^ "Dine Inside of an Old Bank Vault when You Visit This Fantastic Virginia Restaurant". 4 April 2019.
  24. ^ "The Vault Bar & Lounge".

Further reading[edit]


  • Steele, Sean P., Heists: Swindles, Stickups, and Robberies that Shocked the World. New York: Metrobooks, 1995. ISBN 1-56799-170-X.
  • Tchudi, Stephen, Lock & Key: The Secrets of Locking Things Up, In, and Out. New York: Charles Scribner's Sons, 1993. ISBN 0-684-19363-9.


External links[edit]