A rupture disk, also known as a pressure safety disc, burst disc, bursting disc, or burst diaphragm, is a non-reclosing pressure relief safety device that, in most uses, protects a pressure vessel, equipment or system from overpressurization or potentially damaging vacuum conditions.

A rupture disk is a type of sacrificial part because it has a one-time-use membrane that fails at a predetermined differential pressure, either positive or vacuum. The membrane is usually made out of metal, but nearly any material (or different materials in layers) can be used to suit a particular application. Rupture disks provide instant response (within milliseconds or microseconds in very small sizes) to an increase or decrease in system pressure, but once the disk has ruptured it will not reseal. Major advantages of the application of rupture disks compared to using pressure relief valves include leak-tightness, cost, response time, size constraints, and ease of maintenance.

Rupture disks are commonly used in petrochemical, aerospace, aviation, defense, medical, railroad, nuclear, chemical, pharmaceutical, food processing and oil field applications. They can be used as single protection devices or as a secondary relief device for a conventional safety valve; if the pressure increases and the safety valve fails to operate or can not relieve enough pressure fast enough, the rupture disk will burst. Rupture disks are very often used in combination with safety relief valves, isolating the valves from the process, thereby saving on valve maintenance and creating a leak-tight pressure relief solution. It is sometimes possible and preferable for highest reliability, though at higher initial cost, to avoid the use of emergency pressure relief devices by developing an intrinsically safe mechanical design that provides containment in all cases.

Although commonly manufactured in disk form, the devices also are manufactured as rectangular panels ('rupture panels', 'vent panels' or explosion vents) and used to protect buildings, enclosed conveyor systems or any very large space from overpressurization typically due to an explosion. Rupture disk sizes range from 0.125 in (3 mm) to over 4 ft (1.2 m), depending upon the industry application. Rupture disks and vent panels are constructed from carbon steel, stainless steel, hastelloy, graphite, and other materials, as required by the specific use environment.

Rupture disks are widely accepted throughout industry and specified in most global pressure equipment design codes (American Society of Mechanical Engineers (ASME), Pressure Equipment Directive (PED), etc.). Rupture disks can be used to specifically protect installations against unacceptably high pressures or can be designed to act as one-time valves or triggering devices to initiate with high reliability and speed a sequence of actions required.