1112.14 Rating of Rupture Members and Fusible Plugs — 2025 California Mechanical Code

Plugs. The rated discharge capacity of a rupture member or fusible plug discharging to the atmosphere under critical flow conditions, in pounds of air per minute (kg/s), shall be determined in accordance with the following formulas:

C = 0.64 P l d [2] [Equation 1112.14(1)]

d = 1.25 √ C / P l [Equation 1112.14(2)]

Where:

C = Rated discharge capacity expressed as mass flow of air, pounds per minute.

d = Smallest of the internal diameter of the inlet pipe, retaining flanges, fusible plug, and rupture member , inches.

For rupture members:

[Equation 1112.14(3)]

P1 = (rated pressure in psig x 1.1) + 14.7 psia

For fusible plugs:

P1 = Absolute saturation pressure corresponding to the stamped temperature melting point of the fusible plug or the critical pressure of the refrigerant used, whichever is smaller, pound-force per square inch atmosphere, psia. [ASHRAE 15:9.7.7]

For SI units:1 pound per minute = 0.00756 kg/s