The case of Resurfice Corp. v. Hanke involves a tragic injury to a young man who placed a water hose into the gasoline tank of an ice-resurfacing machine rather than the water tank. Vaporized gasoline was released into the air and was ignited by an overhead heater, causing an explosion and fire. Ralph Robert Hanke was badly burned. He sued the manufacturer and distributor of the ice-resurfacing machine, contending that the gasoline tank and the water tank were similar in appearance and placed close together so as to make it easy to confuse the two.

Upheld by the Supreme Court of Canada, the trial judge found that it was not reasonably foreseeable that an operator of the ice-resurfacing machine at issue would mistake the gas tank and the hot water tank. The trial judge based his conclusion on the evidence, including the different size of the two tanks (and that one was taller than the other), and on the fact that the gas tank had a label on it and that Mr. Hanke admitted knowing the difference between the two tanks.

The unanimous judgment of the Supreme Court, written by Chief Justice McLachlin, clearly analyzes the facts and law with reference to foreseeability and causation. Below is an edited portion of her lucid remarks on the “but for” test:

Much judicial and academic ink has been spilled over the proper test for causation in cases of negligence. It is neither necessary nor helpful to catalogue the various debates. It suffices at this juncture to simply assert the general principles that emerge from the cases.

First, the basic test for determining causation remains the “but for” test. This applies to multi-cause injuries. The plaintiff bears the burden of showing that “but for” the negligent act or omission of each defendant, the injury would not have occurred. Having done this, contributory negligence may be apportioned, as permitted by statute.

This fundamental rule has never been displaced and remains the primary test for causation in negligence actions. The “but for” test recognizes that compensation for negligent conduct should only be made “where a substantial connection between the injury and defendant’s conduct” is present. It ensures that a defendant will not be held liable for the plaintiff ’s injuries where they “may very well be due to factors unconnected to the defendant and not the fault of anyone”: Snell v. Farrell, at p. 327, per Sopinka J.

However, in special circumstances, the law has recognized exceptions to the basic “but for” test, and applied a “material contribution” test. Broadly speaking, the cases in which the “material contribution” test is properly applied involve two requirements. First, it must be impossible for the plaintiff to prove that the defendant’s negligence caused the plaintiff ’s injury using the “but for” test. The impossibility must be due to factors that are outside of the plaintiff ’s control; for example, current limits of scientific knowledge. Second, it must be clear that the defendant breached a duty of care owed to the plaintiff, thereby exposing the plaintiff to an unreasonable risk of injury, and the plaintiff must have suffered that form of injury. In other words, the plaintiff ’s injury must fall within the ambit of the risk created by the defendant’s breach. In those exceptional cases where these two requirements are satisfied, liability may be imposed, even though the “but for” test is not satisfied, because it would offend basic notions of fairness and justice to deny liability by applying a “but for” approach.

These two requirements are helpful in defining the situations in which an exception to the “but for” approach ought to be permitted. [Emphasis added.] The Supreme Court then gave two examples to assist in demonstrating the twin principles it had enunciated and found that, in this case, the Court of Appeal erred in applying the material contribution test in circumstances where its use was neither necessary nor justified, and found that the court below erred in failing to recognize that the basic test for causation remains the “but for” test.