(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:[GRAPHIC] [TIFF OMITTED] TC13NO91.047 where: Q = Minimum required rate of discharge in cubic feet per minute of free
air at standard conditions (60 [deg]F and 14.7 psia).M = Molecular weight of the product, or 86.7.T = Temperature, degrees Rankine (460[deg] + temperature in degrees F of
gas at relieving temperature), or 710[deg] 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. Table 1--Minimum emergency venting capacity in cubic feet: free air/hour
(14.7 lb/in\2\a and 60 [deg]F)------------------------------------------------------------------------
Exposed area Cubic feet free Exposed area Cubic feet free
square feet \1\ air per hour square feet \1\ air per hour------------------------------------------------------------------------
20 27,600 275 237,000
30 38,500 300 256,000
40 48,600 350 289,500
50 58,600 400 322,100
60 67,700 450 355,900
70 77,000 500 391,000
80 85,500 550 417,500
90 94,800 600 450,000
100 104,000 650 479,000
120 121,000 700 512,000
140 136,200 750 540,000
160 152,100 800 569,000
180 168,200 850 597,000
200 184,000 900 621,000
225 199,000 950 656,000
250 219,500 1,000 685,000------------------------------------------------------------------------\1\ Interpolate for intermediate sizes. [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]