Theories Of Product Liability In Tort
There are three basic theories of product liability in tort (setting aside breach of warranty claims) under state law in most U.S. states.
Defective manufacturing. In this theory, there was a flaw in making the product that caused it not to conform to an otherwise good design, causing harm to the claimant.
For example, if a fire alarm is designed to have a trigger that actives at a certain temperature, but the noise maker in the alarm melts and becomes inoperative at a temperature below the trigger temperature because the manufacturer uses plastic instead of the design requirement of metal for a part because of a temporary shortage of that metal, the manufacturer is liable for harm that results from the fire alarm's failure to activate at the trigger temperature.
Defective design. In this theory, there was a flaw in the design of the product and that flaw caused harm to the claim and would have done so even if the product was perfectly manufactured consistently with the design.
What constitutes a defective design?
A company's liability for a design defect occurs when there was a
foreseeable risk posed by the product when the product was
manufactured as intended and used for its intended purposes.
In many states, plaintiffs also have to show that the risk could have
been reduced or avoided by the adoption of a reasonable alternative
design, which was:
Feasible, in other words, the manufacturer had the ability to produce
it; Economically feasible, in other words, it would not cost too much
to make the product with the modification; and
Not in opposition to the product's intended purpose, in other words,
the product would still perform the function for which it was created.
For example, if a whiskey distilling vat generates high internal pressures that could cause it to explode if not alleviated, and the manufacturer does not include a pressure release valve in the design to prevent that explosion, the manufacturer would be liable for the harm caused by an explosion that occurs because there is not a pressure release valve in the design making it defective.
Also, failure to comply with a regulatory standard intended to enhance safety in a design when that non-compliance causes harm (e.g. designing a car without seat belts), may be a design defect as a matter of law. Likewise, failure to comply with widely recognized non-legally adopted design standards in an industry intended to enhance safety in designs of particular kinds of products, when that non-compliance causes harm, will usually constitute open and shut proof of a design defect without further proof or analysis.
Failure to warn. In this theory, the design of the product presents risks of harm to the user that are not obvious, which would be mitigated or eliminated if the user was given an adequate warming of the risk and followed that warning.
For example, while the risk of harm from a knife is obvious and does not trigger a duty to warn, if a knife is made from a material that creates a toxic cloud of chlorine gas when exposed to bleach, the maker of a knife with this non-obvious risk needs to adequately warn potential users of the knife of the importance of not exposing it to bleach or the maker of the knife will have liability for bleach related harms to users that occur.
Product liability in tort is "strict" in the sense that there can be liability even if the manufacturer was not negligent.
For example, in a defective manufacturing case, even if the manufacturer had the best quality control system in the world, if one item in a billion is defectively manufactured and causes harm as a result, the manufacturer is still liable.
Similarly, in a defective design case, it is not a defense that a reasonable product designer took reasonable care to identify defects (e.g. holding brain storming sessions and reading any relevant studies) that didn't actually reveal the potential problem, if the design defect was foreseeable but the designer just didn't think of it anyway.
And, in a failure to warn case, there can be liability even if the manufacturer was "reasonable" in the sense of providing the warnings customarily used by others in the industry but still fails to warn of a non-obvious risk that causes harm.
Are they only liable if the product malfunctions in an unexpected and
unpredictable way (e.g., the board breaks)?
Not exactly. But if the product is causes harm while carrying out its intended purpose, that isn't a malfunction or defect. A gun isn't defective because it can be used to intentionally kill someone or commit suicide.
Does liability only apply when a product injures a user, but not when
the users injures themselves using a product where harm cannot be
There is not liability if the user is not injured. If the user injures themselves using the product for the intended purpose this is also not a product liability issue unless the harm could have been avoided with a design change or warning of a non-obvious risk.
Can they absolve themselves of liability by simply warning the user
If a product has a design defect, merely warning a user of the design defect will usually not relieve the manufacturer from liability.
For example, stating that the whiskey vat doesn't have a pressure relief valve and could explode, when it could have been designed with them with a $2 manufacturing cost change, won't relieve the manufacturer from liability if someone is harmed by the vat exploding because it doesn't have a pressure relief valve.
In reality, there are gray areas where an alleged design defect that can be fully mitigated with a warning is really a design defect, but that's why we have judges, juries, and expert witnesses to resolve close cases where there are arguments to be made either way.
A skateboard does have risks even when used for its intended purpose, most of which are obvious, but some of which (e.g. getting clothing entangled in a wheel) might not be. When there is no feasible way to eliminate the risks that are present, and warnings are provided when there are non-obvious risks, then there is no liability on the part of the manufacturer of the skateboard.