46 CFR §64.63

1. (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:
2. (b)The total emergency venting capacity (Q) of an insulated portable tank may have a reduction if—
   1. (1)It is shown to the Coast Guard that the insulation reduces the heat transmission to the tank;
   2. (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. (3)The insulation is sheathed.