Manufacturers can be, and often are, held liable for injuries caused by products that were defectively designed. The question is whether the designer used reasonable care in designing a product reasonably safe for its foreseeable use. The concern over reasonableness and standards of care are elements of negligence theory.
Defective-design cases can pose severe problems for manufacturing and safety engineers. More safety means more cost. Designs altered to improve safety may impair functionality and make the product less desirable to consumers. At what point safety comes into reasonable balance with performance, cost, and desirability (see Figure 17.3) is impossible to forecast accurately, though some factors can be taken into account. For example, if other manufacturers are marketing comparable products whose design are intrinsically safer, the less-safe products are likely to lose a test of reasonableness in court.