The part that confuses people most is that a state law does not have to directly conflict with federal law to be pushed aside. Federal preemption happens when federal law controls an issue so strongly that state law cannot operate, either because Congress clearly said so, because state and federal rules clash, or because federal regulation is so complete that there is little room left for states to add their own rules. The idea comes from the Supremacy Clause of the U.S. Constitution, which makes valid federal law superior to conflicting state law.

In practice, preemption can decide which safety rules apply and whether a person can sue under state law at all. It comes up in areas like railroad crossings, aviation, medical devices, interstate trucking, and some workplace regulations. A state may still enforce its own rules where federal law leaves room, but not where those rules interfere with a federal scheme.

For an injury claim in Oregon, preemption can affect both the legal theory and the available damages. A plaintiff may still bring a negligence or product liability claim, but a defendant may argue that federal standards block part of the case. That can narrow the evidence, limit state-law duties, or shift the dispute into federal court. Preemption does not replace Oregon's own fault rules, such as the state's modified comparative fault system with a 51% bar, but it can determine whether Oregon law applies in the first place.