A site where drums periodically descend a ramp while employees ascend ladders is a struck-by exposure on a schedule, and struck-by events are among the leading causes of construction fatalities. The controls are unglamorous and they are not optional.
The drums should never be in motion. All materials stored in tiers must be stacked, racked, blocked, interlocked, or otherwise secured to prevent sliding, falling or collapse (29 CFR 1926.250(a)(1)). Drums and other round stock get chocked, racked, or stored on end; a ramp is an inclined plane, and an unsecured drum on one is a hazard waiting for a reason. The housekeeping rule also requires debris to be kept cleared from work areas, passageways, and stairs (29 CFR 1926.25(a)), and a ramp that doubles as a drum chute is not a clear passageway.
The people below. Employees working where there is a possible danger of head injury from impact or from falling or flying objects must be protected by protective helmets (29 CFR 1926.100(a)). Hard hats are required under these conditions, but the engineering answer is to remove the condition, not to armor the crew against it. The ladders themselves must meet Subpart X: used only on stable and level surfaces unless secured (29 CFR 1926.1053(b)(6)), with the area around the top and bottom kept clear (29 CFR 1926.1053(b)(9)). A ladder foot in the path of rolling drums fails both.
Why it kept happening. The construction general provisions require the employer's accident prevention program to provide for frequent and regular inspections of the job site, materials, and equipment by competent persons (29 CFR 1926.20(b)(2)), and require each employee to be instructed in the recognition and avoidance of unsafe conditions (29 CFR 1926.21(b)(2)). A hazard that recurs is, by that point, a program failure as much as a storage failure.
When a hazard is rhythmic and predictable, crews get tempted to treat timing their movements as the control. The standards never accept timing as a control. Secure the source, clear the path, protect the head, and find out who keeps leaving drums at the top of the ramp.