Houston Aquarium, Inc., operates a four-story entertainment complex in Houston, Texas, known as the “Downtown Aquarium.” The complex houses several large tanks displaying various species of marine life, as well as bird and reptile exhibits, a restaurant, and rides such as a train and carrousel. Following an inspection of the Downtown Aquarium, the Occupational Safety and Health Administration issued Houston Aquarium a citation alleging six serious violations of the Commercial Diving Operations standard, 29 C.F.R. Part 1910, Subpart T. The Secretary grouped these violations into five citation items, one of which he withdrew before the hearing (Item 2); a total penalty of $19,800 is proposed for the remaining items. The five citation items collectively allege that violations of five provisions of the diving standard occurred in six of the complex’s aquatic tanks.