Glossary of Terms


Atmosphere Explosive. An abbreviation that is used in connection with two European Directives concerning production of equipment and safety systems for use in potentially explosive atmospheres and safety for personnel working in potentially explosive atmospheres.

Back Pressure

The static pressure existing at the outlet of a rupture disc device at the time the device bursts or vents. Where pressure is below atmospheric pressure, this can be termed Vacuum Presure.

Back Pressure Support

Component of a rupture disc device which prevents failure of the rupture disc due to pressure differential in a reverse direction. Where system pressure is below atmospheric pressure, this can be known as vacuum support.


A quantity of rupture discs made as a single group to the same specifications and from the same lot of material.

Explosion Vent (Bursting Panel)

An explosion vent is a device used for protection against excessive internal, explosion-incurred pressures, by means of pressure relief. An Explosion vent will relieve pressure from the instant its opening (or activation) pressure p has been exceeded.

Rupture Disc (Bursting Discs)

A non-reclosing element designed to burst or rupture at a predetermined pressure to protect systems or individual plant from unacceptable levels of pressure or vacuum.

Rupture Disc Assembly

The complete assembly of components which are installed into the holder to perform the desired function.

Rupture Disc Device

A non-reclosing pressure relief device actuated by differential pressure and designed to function by the bursting or venting of the rupture disc(s). It is the complete assembly of installed components, including where appropriate the rupture disc holder.

Rupture Disc Holder

The part of a rupture disc device which ensures the proper performance of the rupture disc and accommodates its installation into a system.

Bursting Pressure

The value of the pressure differential across the rupture disc at which a rupture disc functions.


A layer of metallic or non-metallic material applied to components of a rupture disc device (not a liner)

Coincident Temperature (Burst Temperature)

The temperature used in conjunction with a bursting pressure.

Conventional (Forward Acting) Rupture Disc

A rupture disc designed to fail when a build up of pressure in the system exceeds the tensile strength of the disc material (tension loaded). A conventional rupture disc may be flat or domed. A conventional domed rupture disc is domed in the direction of the bursting pressure (ie where the bursting pressure is applied to the concave side of the bursting disc).

Discharge Capacity

The rate at which a rupture disc device discharges a fluid after bursting or venting of the rupture disc assembly.


The sheet or strip used for the manufacture of metallic rupture discs.

Free-Flow (Discharge) Area

The area which is the minimum cross-sectional flow area of the rupture disc device taking into consideration the possible reduction of area by back pressure supports, catching devices and parts of the rupture disc which remain after bursting or venting.

Ingress Protection (IP)

An international classification system for the sealing effectiveness of closures of electrical equipment against the intrusion into the equipment of foreign bodies (i.e dust and moisture)


An additional sheet or sheets of material forming part of the rupture disc assembly or holder (not a coating)

Manufacturing Range

Range of pressure within which the average bursting pressure of a batch of rupture discs shall fall in order to be acceptable for a particular application as agreed between manufacturer and customer.

Maximum Operating Pressure

This is the maximum system pressure to which the disc may be exposed without causing premature metal fatigue to the rupture disc. Maximum operating pressures are typically between 50% and 100% of the rated burst pressure of the disc, depending on the type of disc. This is also known as Maximum Operating Pressure to Burst Pressure Ratio.

Operating Pressure (Working Pressure)

The pressure which the rupture disc is exposed to during normal operation

Operating Temperature (Working Temperature)

The nominal temperature which the rupture disc is exposed to during normal operation

Performance Tolerance

The difference between the maximum and minimum specified bursting pressures at a coincident temperature. Burst tolerance” is the allowable deviation in actual burst pressure from the “marked burst pressure”. Typically expressed as a percentage (or in “psig”), a disc properly specified and installed should always burst within the “tolerance” for the particular type, style, and rated pressure of the disc

Relieving Pressure

The maximum pressure under discharge conditions in the pressurised system (can differ from burst pressure).

Relieving Temperature

The maximum temperature under discharge conditions in the pressurised system (can differ from burst temperature).

Reverse Acting (Buckling) Rupture Disc

A rupture disc which is domed against the direction of the bursting pressure ie where the bursting pressure is applied to the convex side of the rupture disc and designed to fail under compression by buckling, bending or shearing forces.

Composite (Slotted Lined) Rupture Disc

A conventional rupture disc made up of two or more layers, one of which is slit or slotted so as to reduce its strength and to control the bursting pressure of the rupture disc. May be flat or domed.

Specified Burst Pressure

The pressure quoted by the user or the manufacturer with a coincident temperature when specifying the burst disc performance or requirement. May be specified as a minimum or maximum value.


A term used to describe telecommunications in which electromagnetic waves (rather than some form of wire) carry the signal over part or all of the communication path.