U.S. Code of Federal Regulations
Regulations most recently checked for updates: Sep 16, 2025
(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:
(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/in 2a and 60 °F]
| Exposed area
square feet 1 | Cubic feet free air
per hour | Exposed area
square feet 1 | Cubic feet free 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.
