Question 1: 29 CFR 1910.159(c)(10) in part states, The minimum vertical clearance between sprinklers and material below shall be 18-inches (45.7 cm). Does this apply only to materials placed directly below the sprinkler heads? Response 1: No. The 18-inch vertical clearance requirement is treated as a horizontal plane throughout the storage area or room. All materials must be stored below this horizontal plane.