General construction requirements.

(a) The outer shell must be of straight-sided steel, with welded body seams, and may be either a single sheet of steel, or may be fabricated by welding together two appropriate lengths of drums with each length to contain 3 swedged or rolled rolling hoops as prescribed for either of these specifications. A removable head for a packaging of 210 L (55 gallons) or larger volume must have one or more corrugations in the cover near the periphery. For a packaging exceeding 57 L (15 gallons) volume, the head must be crowned (convexed), not extending beyond the level of the chime, with a minimum convexity of 1 cm (3/8-inch).

(1) The maximum authorized gross weight, metal thickness, and minimum end insulation thickness for the marked volume is as follows:

Marked capacity Gallons not over Liters Maximum authorized gross weight Pounds Kilograms Minimum thickness of uncoated sheets and heads (gauge) Minimum thickness of end insulation Inches Cm 15 57 160 73 20 1.88 4.7 30 114 480 219 18 3.75 9.5 55 210 640 292 16 3.75 9.5 110 420 640 292 16 3.75 9.5

(2) Each drum must have at least four 1.2 centimeter (0.5-inch) diameter vents near the top, each covered with a weatherproof tape or fusible plug; or equivalent device. A layer of porous refractory fiber may be placed behind the pressure-relief vent holes.

(b) Inner containment vessel must conform to specification 2R or equivalent (cast iron or brass are prohibited), with maximum usable inside diameter of 13.3 cm (5.25 inches), minimum usable inside diameter of 10 cm (4 inches), and minimum height of 15 cm (6 inches).

(c) Inner containment vessel must be fixed within the outer shell by one of the following types of solid centering media, with the sides of the inner vessel protected by at least 9.5 cm (3.75 inches) of insulation media, and the ends with at least the thickness as prescribed in paragraph (a)(1) of this section.

(1) Machined discs and rings made of solid industrial cane fiberboard having a density of at least 0.24 g/cc (15 pounds per cubic foot) fitted such that the radial clearances between the fiberboard, inner vessel, and shell do not exceed 6 mm (1/4-inch); or

(2) Hardwood or plywood at least 1.2 centimeter (1/2-inch) thick, having a density of at least 0.45 g/cc (28 pounds per cubic foot). There must be no gap or direct heat path from the shell to the inner vessel.

(d) Any radiation shielding material used must be placed within the inner containment vessel or must be protected in all directions by at least the thickness of the thermal insulating material prescribed in paragraph (a) of this section.

(e) For a packaging having an authorized gross weight in excess of 219 kg (480 pounds), a steel bearing plate, at least 6 mm (0.25-inch) thick or a plywood disc, at least 2.5 cm (1-inch) thick, and at least 25 cm (10 inches) in diameter must be provided at both ends and adjacent to the specification 2R inner containment vessel, to provide additional load-bearing surface against the insulation-centering medium.

[Amdt. 178-1, 33 FR 14935, Oct. 4, 1968, as amended by Amdt. 178-35, 39 FR 45246, Dec. 31, 1974; 40 FR 44327, Sept. 26, 1975. Redesignated by Amdt. 178-97, 55 FR 52716, Dec. 21, 1990, as amended at 63 FR 37462, July 10, 1998; 66 FR 45387, Aug. 28, 2001; 67 FR 61016, Sept. 27, 2002]