{"data":{"id":"us/46-cfr-64.63","jurisdiction":"us","citation":"46 CFR 64.63","heading":"Minimum emergency venting capacity.","body":"(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:\nFormula 1 to Paragraph (a)\nWhere:\nQ = Minimum required rate of discharge in cubic feet per minute of free air at standard conditions (60 °F and 14.7 psia).\nM = Molecular weight of the product, or 86.7.\nT = Temperature, degrees Rankine (460° + temperature in °F of gas at relieving temperature), or 710 °R.\nA = Total external surface area of the tank compartment in square feet.\nL = Latent heat of the product being vaporized at relieving conditions in Btu per pound, or 144 Btu per pound.\nZ = Compressibility factor of the gas at relieving conditions, or 1.0.\nC = Constant based on relation of specific heats, equal to 315.\n(b) The total emergency venting capacity (Q) of an insulated portable tank may have a reduction if—\n(1) It is shown to the Coast Guard that the insulation reduces the heat transmission to the tank;\n(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\n(3) The insulation is sheathed.\nTable 1 to § 64.63—Minimum Emergency Venting Capacity in Cubic Feet: Free Air/Hour\n[14.7 lb/in2 a and 60 °F]\nExposed area square feet 1 Cubic feet free air per hour Exposed area square feet 1 Cubic feet free air per hour\n20 27,600 275 237,000\n30 38,500 300 256,000\n40 48,600 350 289,500\n50 58,600 400 322,100\n60 67,700 450 355,900\n70 77,000 500 391,000\n80 85,500 550 417,500\n90 94,800 600 450,000\n100 104,000 650 479,000\n120 121,000 700 512,000\n140 136,200 750 540,000\n160 152,100 800 569,000\n180 168,200 850 597,000\n200 184,000 900 621,000\n225 199,000 950 656,000\n250 219,500 1,000 685,000\n1 Interpolate for intermediate sizes.","path":["Title 46—Shipping","CHAPTER I—COAST GUARD, DEPARTMENT OF HOMELAND SECURITY","SUBCHAPTER F—MARINE ENGINEERING","PART 64—MARINE PORTABLE TANKS AND CARGO HANDLING SYSTEMS","Subpart C—Pressure Relief Devices and Vacuum Relief Devices for MPTs"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-46.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:26:22Z","sha256":"5982a213a7d6ec7aecd4d4b7acaa69ba6f69a326ac2bd00d68ea653fe5c8fe96","source_id":"us-cfr","stale":true,"prev":"us/46-cfr-64.61","next":"us/46-cfr-64.65"},"notice":"GroundRules: Original legal text. Not legal advice."}