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Firestopped cable penetration in a bulkhead which is required to have a fire-resistance rating, on board a BC Ferries ship, British Columbia, Canada. The firestop is made of a purpose-designed putty on the outside and a proprietary cementitious fill on the inside.

A bulkhead is an upright wall within the hull of a ship. Other kinds of partition elements within a ship are decks and deckheads.

Bulkheads in a ship serve several purposes: They increase the structural rigidity of the vessel, divide functional areas into rooms and create watertight compartments that can contain water in the case of a hull breach or other leak. Some bulkheads and decks are fire-resistance rated to achieve compartmentalisation, a passive fire protection measure.

Openings in fire-resistance rated bulkheads and decks must be firestopped to restore the fire-resistance ratings that would otherwise be compromised, if the openings were left unsealed. The Authority 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 fully grounded (electrically) as a countermeasure against damage from EMI and EMP due to nuclear or electromagnetic bomb detonations near the ship, which could severely damage the vital electronic systems on a ship.

In the case of firestops, cable jacketing is typically removed within the seal and firestop rubber modules are internally fitted with copper shields, which contact the cables' armour in order to ground the seal. There are also conductive fill materials in use for that purpose, which must be in direct contact with cable armour to ensure full grounding of the bulkheads and decks. Any openings that are not fully grounded would defeat that purpose.

The word bulki meant "cargo" in Old Norse. The Song Dynasty Chinese author Zhu Yu wrote of Chinese ships with watertight bulkhead compartments in his book Pingzhou Table Talks of 1119 AD. A Chinese trade ship dated to 1277 AD was found off the southern coast of China in 1973, and had 12 bulkhead compartment rooms in its hull. Sometime in 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." Now, by extension, the term applies to every vertical panel aboard a ship, except for the hull itself.

The term was later applied to other vehicles, such as trams, automobiles, aircraft or spacecraft, as well as to containers, such as fuel tanks. In some of these cases bulkheads are airtight to prevent air leakage or the spread of a fire.

• fire protection
• fireproofing
• intumescent
• passive fire protection
• rear pressure bulkhead
• structural steel