Was Barham's final blast a magazine or boiler explosion?

What caused HMS Barham's final catastrophic explosion?

The inquiry favored a 4-inch magazine igniting a 15-inch magazine, but the evidence also permits a boiler explosion caused by the clustered torpedo impacts, possibly alongside the magazine detonation.

The board of inquiry concluded that a 4-inch magazine set off a 15-inch magazine. A simultaneous boiler explosion is also considered plausible because of the torpedo hit positions and the shape and scale of the final blast. Postwar simulations of such concentrated hits are said to show severe shock and internal spalling, with metal fragments capable of damaging both magazines and boilers. That supports a possible mechanism without establishing what happened aboard Barham. The inquiry finding remains the preferred account, while combined boiler and magazine involvement remains an unproven interpretation.