Tools and machines, simple and complex, carry risks. Manufacturers have an obligation to design their products to eliminate the most obvious risks, for example, placing effective hand guards on power tools. Obviously, though, the ways in which tools and machines may be used are many. Mechanical design safety measures have some practical limits, not the least of which is financial.
One the simplest and most economical ways that manufacturers can prevent many injuries, is by placing adequate warnings on their products. Warnings remind the user of the product to be cautious and to avoid behaviors known by the manufacturer to be dangerous. Take a cherry picker, for example. The manufacturer knows that it will frequently be used at the level of power lines. It is not hard to imagine an obligation that a warning appear in some strategic spot on the machine, telling the user to avoid contact with power lines. In order to be effective, a warning must be designed to prevent or change behavior. To that end, it must be placed where it is likely to be read, must be large enough and/or obvious enough that is easily seen, and it must be easy to understand. Some research suggests that the use of pictures as well as words carries the highest likelihood of success.
Juries are most open to failure to warn theories when the potential danger would not necessarily be obvious to the user and where the product user was not excessively negligent themselves. A failure to warn allegation in the case of a dangerous product can be especially powerful when the manufacturer was aware of multiple injuries do to certain types of uses or conduct with its product, and simply failed to add a warning to minimize future harm.