Which method meets the loading rule for cylinders containing Class 2 gases?
Correct answer: D – Securely restrain them upright or horizontally, use racks, or pack them in boxes or crates
Federal rules require Class 2 gas cylinders to be securely restrained upright or horizontally, loaded in racks, or packed in boxes or crates to prevent shifting, overturning, or ejection. A vehicle without a floor or platform must have suitable securing racks. When a pressure-relief device is installed on a cylinder containing Division 2.1 flammable gas, it must communicate with the vapor space.
Source: 49 CFR § 177.840(a)(1) — Class 2 (gases) materials.

