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.

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.

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 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.


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, controls, 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 relies 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



Fichet Paris, Vault of Crédit Lyonnais

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 is 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 safeguarded separately and joined 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


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


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



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". 6 March 2015. Archived from the original on 16 April 2020. Retrieved 10 August 2018.
  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. Archived from the original on 13 August 2011. 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.org. NPR. Archived from the original on 6 August 2005. 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. Archived (PDF) from the original on 14 March 2005. Retrieved 28 December 2010.
  12. ^ Scott Selby & Greg Campbell (2010). Flawless: Inside the Largest Diamond Heist in History. Sterling. pp. 148–149. Archived from the original on 15 August 2021. Retrieved 24 August 2021.
  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. Archived (PDF) from the original on 16 April 2020. Retrieved 4 September 2017.
  15. ^ "Red Book Live, Part 4, Section 2" (PDF). LPCB. Archived (PDF) from the original on 4 September 2017. 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". shop.bsigroup.com. Archived from the original on 4 September 2017. Retrieved 4 September 2017.
  17. ^ Standards, European. "EN 1143-1". Archived from the original on 4 September 2017. Retrieved 4 September 2017.
  18. ^ "EN 1300 Locks". www.ecb-s.com. Archived from the original on 18 April 2018. Retrieved 5 September 2017.

Further reading



  • 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.