What is the test for strict liability under Rylands v. Fletcher?

Returning to the merits of the strict liability theory adopted by the trial judge, we begin by distinguishing the risk that is targeted by that theory from the risk targeted by the rule in Rylands v. Fletcher. Strict liability under Rylands v. Fletcher aims not at all risks associated with carrying out an activity, but rather with the risk associated with the accidental and unintended consequences of engaging in an activity. The Rylands v. Fletcher cases are about floods, gas leaks, chemical spills, sewage overflows, fires and the like. They hold that where the defendant engages in certain kinds of activities, the defendant will be held strictly liable for damages that flow from mishaps or misadventures that occur in the course of that activity. The escape requirement in Rylands v. Fletcher connotes something unintended and speaks to the nature of the risk to which the strict liability in Rylands v. Fletcher attaches: see The Law of Nuisance in Canada, at pp. 132, 137. [page347]