In the case of Sienkiewicz v Greif the Court of Appeal considered the position of a claimant who was exposed to asbestos in a factory in Ellesmere Port.  It was argued by the defendant employer that the exposure to asbestos was minimal, and was less than the environmental exposure in the Ellesmere Port area at that time. The defendant therefore tried to argue that to establish liability,  the claimant must show that the risk associated with the exposure at work had more than doubled her existing risk of exposure.

Held, it was unreasonable to require the claimant to prove causation by reference to a twofold increase in risk - it was sufficient to show that the tortious exposure had "materially increased the risk".