Abulkhead is an upright wall within thehull of a ship, within thefuselage of anairplane, or a car. Other kinds of partition elements within a ship aredecks anddeckheads.

The wordbulki meant "cargo" inOld Norse. During the 15th century sailors and builders in Europe realized that walls within a vessel would prevent cargo from shifting during passage. In shipbuilding, any vertical panel was called a head. So walls installed abeam (side-to-side) in a vessel's hull were called "bulkheads".^{[dubious –discuss]} Now, the termbulkhead applies to every vertical panel aboard a ship, except for the hull itself.

Bulkheads were known to the ancient Greeks, who employed bulkheads in triremes to support the back of rams. By the Athenian trireme era (500 BC),^[1] the hull was strengthened by enclosing the bow behind the ram, forming a bulkhead compartment. Instead of using bulkheads to protect ships against rams, Greeks preferred to reinforce the hull with extra timber along the waterline, making larger ships almost resistant to ramming by smaller ones.^[2]

Bulkhead partitions are considered to have been a feature of Chinesejunks, a type of ship. Song dynasty authorZhu Yu (fl. 12th century) wrote in his book of 1119 that thehulls ofChinese ships had a bulkhead build. The 5th-century bookGarden of Strange Things by Liu Jingshu mentioned that a ship could allow water to enter the bottom without sinking. Archaeological evidence of bulkhead partitions has been found on a 24 m (78 ft) long Song dynasty ship dredged from the waters off the southern coast of China in 1973, the hull of the ship divided into twelve walledcompartmental sections builtwatertight, dated to about 1277.^[3][4]

Texts written by writers such asMarco Polo (1254–1324),Ibn Battuta (1304–1369),Niccolò Da Conti (1395–1469), andBenjamin Franklin (1706–1790) describe the bulkhead partitions of East Asian shipbuilding.^[3][5] An account of the early fifteenth century describes Indian ships as being built in compartments so that even if one part was damaged, the rest remained intact—a forerunner of the modern day watertight compartments using bulkheads.^[6]

As wood began to be replaced by iron in European ships in the 18th century, new structures, like bulkheads, started to become prevalent.^[7] Bulkhead partitions became widespread in Western shipbuilding during the early 19th century.^[3]Benjamin Franklin wrote in a 1787 letter that "as these vessels are not to be laden with goods, their holds may without inconvenience be divided into separate apartments, after the Chinese manner, and each of these apartments caulked tight so as to keep out water."^[8] A 19th-century book on shipbuilding attributes the introduction of watertight bulkheads to Charles Wye Williams, known for hissteamships.^[9]

Bulkheads in a ship serve several purposes:

• increase the structural rigidity of the vessel,
• divide functional areas into rooms and
• createwatertight compartments that cancontain water in the case of a hull breach or other leak.
• some bulkheads anddecks arefire-resistance rated to achievecompartmentalisation, apassive fire protection measure; seefirewall (construction).

Not all bulkheads are intended to be watertight, in modern ships the bottom floor is supported against the hull by transverse walls(bulkheads) and longitudinal walls, being common to use bulkheads with lightening holes.^[10]

On an aircraft, bulkheads divide the cabin into multiple areas. On passenger aircraft a common application is for physically dividing cabins used for different classes of service (e.g.economy andbusiness.) On combination cargo/passenger, or "combi" aircraft, bulkhead walls are inserted to divide areas intended for passenger seating and cargo storage.

Openings in fire-resistance rated bulkheads and decks must befirestopped to restore the fire-resistance ratings that would otherwise be compromised if the openings were left unsealed. Theauthority having jurisdiction for such measures varies depending upon the flag of the ship. Merchant vessels are typically subject to the regulations and inspections of the coast guards of the flag country. Combat ships are subject to the regulations set out by the navy of the country that owns the ship.

Bulkheads and decks of warships may be fullyelectrically grounded as acountermeasure against damage fromelectromagnetic interference andelectromagnetic pulse due to nearby nuclear orelectromagnetic bomb detonations, which could severely damage the vital electronicsystems on a ship.

In the case of firestops, cable jacketing is usually removed within the seal and firestop rubber modules are internally fitted with copper shields, which contact the cables' armour to ground the seal.

Most passenger vehicles and some freight vehicles will have a bulkhead which separates the engine compartment from the passenger compartment or cab;^[11] the automotive use is analogous to the nautical term in that the bulkhead is an internal wall which separates different parts of the vehicle. Some passenger vehicles (particularly sedan/saloon-type vehicles) will also have a rear bulkhead, which separates the passenger compartment from the trunk/boot.

The term was later applied to other vehicles, such asrailroad cars,hopper cars,trams,automobiles,aircraft orspacecraft, as well as tocontainers,intermediate bulk containers andfuel tanks. In some of these cases bulkheads are airtight to prevent air leakage or the spread of a fire. The term may also be used for the "end walls" ofbulkhead flatcars.

Mechanically, a partition or panel through which connectors pass, or a connector designed to pass through a partition.

Inarchitecture the term is frequently used to denote any boxed in beam or other downstand from a ceiling and by extension even the vertical downstand face of an area of lower ceiling beyond. This usage presumably derives from experience on boats where to maintain the structural function personnel openings through bulkheads always retain a portion of the bulkhead crossing the head of the opening. Head strikes on these downstand elements are commonplace, hence in architecture any overhead downstand element comes to be referred to as a bulkhead.

Bulkhead also refers to a moveable structure often found in an Olympic-size swimming pool, as a means to set the pool into a "double-ended short course" configuration, or long-course, depending on the type of event being run. Pool bulkheads are usually air-fillable, but power driven solutions do exist.

The term is also used to refer to large retroactively installed pressure barriers for temporary or permanent use, often during maintenance or construction activities.^[12]

• Britannica definition
• Merriam-Webster definition
• WIPO Bulkhead for motor vehicle
• Canadian Armed Forces Glossary, seeFire Zone, page 5 of 14
• Det Norske Veritas Type Approval for a fire damper inside and A60 bulkheadArchived 2016-04-07 at theWayback Machine
• Subject-related patent by Free Patents Online
• An example treatise on the use of A60 bulkheads onboard tankers.