§ 64.63 — Minimum Emergency Venting Capacity

(a) The total emergency venting capacity (Q) of the relief devices of an uninsulated MPT must be in accordance with table 1 to § 64.63 or the following formula based upon the pressure relief device operating at a pressure not to exceed the test pressure:

Where:

Q = Minimum required rate of discharge in cubic feet per minute of free air at standard conditions (60 °F and 14.7 psia).

M = Molecular weight of the product, or 86.7.

T = Temperature, degrees Rankine (460° + temperature in °F of gas at relieving temperature), or 710 °R.

A = Total external surface area of the tank compartment in square feet.

L = Latent heat of the product being vaporized at relieving conditions in Btu per pound, or 144 Btu per pound.

Z = Compressibility factor of the gas at relieving conditions, or 1.0.

C = Constant based on relation of specific heats, equal to 315.

(b) The total emergency venting capacity (Q) of an insulated portable tank may have a reduction if—

(1) It is shown to the Coast Guard that the insulation reduces the heat transmission to the tank;

(2) The present reduction of the emergency venting capacity (Q) is limited to the percent reduction of the heat transmission to the tank or 50 percent, whichever is less; and

(3) The insulation is sheathed.

Table 1 to § 64.63—Minimum Emergency Venting Capacity in Cubic Feet: Free Air/Hour

[14.7 lb/in2 a and 60 °F]