The 20-inch bypass was therefore clearly not what would have been produced or accepted by a more considered process, but controversy developed (and became acrimonious) as to whether its failure was the initiating fault in the disaster (the 20-inch hypothesis, argued by the plant designers (DSM) and the plant constructors; and favoured by the court's technical advisers), or had been triggered by an external explosion resulting from a previous failure of the 8-inch line (argued by experts retained by Nypro and their insurers).