See Dubai Drydocks
The #2 dock measures 525m long, 100m wide, and 12.3m deep, being the largest of three graving docks. The gate is composed of 28 semi-bouyant flap type or folding panels. When up, these panels are stayed by props set in concrete footings and water pressure. When lowered, the gates fold into the seabed & the props into the sill.
The props, which are inboard of the drydock, have some risk of impact damage (BS 6349-3). Four of the props had been damaged by a barge or tanker strike & where under repair, the shoring of which was possibly inadequate . Allegedly, two engineering companies had considered the damage before the dock was flooded & came to opposing conclusions as to whether the dock should be pumped dry before repairs made .
A number of vessels were present in the docks at the time of flooding, a common practice to increase a graving docks utilization. These vessels were probably not sea-worthy, as tank plugs, overboard & sea-chest valves, etc. are typically opened on dry-docked vessels, and sections of shell plate may have been removed for replacement.
The vessels in the dock at the time where (from forward to the gates);
At 9:30am, two panels collapsed, opening to a 12 meter sea, rapidly flooding the drydock. SEP-350 moved towards the gate, took on a list & grounded. Indira-1 came off its blocks and jammed sideways, while Key Bremuda (forward) was able to float on its hull section. The tanker rose off its blocks, turning side on to the dock. CB-1 rolled and sank.
At least 21 people drowned, however unofficial estimates have been significantly higher due to the use of poorly acknowledged migrant workers.