(a) The total emergency venting capacity (Q) of the relief devices of an uninsulated MPT must be in accordance with Table 1 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 degrees F of gas at relieving temperature), or 710° Rankine. 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, in accordance with appendix J of division 1 of section VIII of the ASME Code, 1974 edition, or 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.

[CGD 73-172, 39 FR 22950, June 25, 1974, as amended by CGD 84-043, 55 FR 37410, Sept. 11, 1990; 55 FR 47477, Nov. 14, 1990]