A product generally has a design defect if, because of its design, (1) it failed to perform as safely as an ordinary user would expect when the product was used in a manner reasonably foreseeable to the manufacturer; and (2) at the time the product was designed, a safer alternative design was available that was technically and economically feasible under the circumstances.

If a product has a design defect, the manufacturer will generally be strictly liable in tort for damages caused by the defective product. This means the manufacturer will be liable even if the manufacturer exercised great care in designing the product and was not negligent.

But even when a product is defective due to a flawed design, some courts will use one of these two tests to determine whether the defendant is liable to the plaintiff:

• Risk-Utility or Risk-Benefit Test. The risk-utility test provides that a defendant is not liable for a design defect if the evidence shows the product’s utility outweighs its inherent risk of harm.

• Consumer Expectation Test. Under the consumer expectation test, the question is whether a reasonable consumer would find the product defective when using the product in a reasonable manner. If a reasonable consumer would not find the product defective when using it in a reasonable manner, the defendant is not liable even if the product’s design flaw caused the plaintiff’s injury.

Products liability laws vary from state to state and may be in a state’s statutes or in its court opinions (also known as case law or common law).

In New Hampshire, product liability law addresses design defects under the principles of strict liability. A product is considered to have a design defect if it fails to perform as safely as an ordinary consumer would expect when used as intended or in a reasonably foreseeable manner, and if a safer alternative design was feasible at the time of its creation. Under strict liability, a manufacturer can be held liable for damages caused by a defective product regardless of the level of care taken during the design process. New Hampshire courts may apply either the Risk-Utility Test or the Consumer Expectation Test to determine liability. The Risk-Utility Test weighs the product's utility against its potential risks, absolving the manufacturer of liability if the utility is deemed to outweigh the risks. The Consumer Expectation Test considers whether a reasonable consumer would find the product defective in normal use. If not, the manufacturer may not be held liable. These principles are derived from state statutes and case law, and they guide how courts handle product liability cases involving design defects in New Hampshire.