Dec 6, 2017


  • Medical device warnings require careful design and communication considerations.
  • Manufacturers should heed warning sign conventions such as signal words.
  • Warnings are not foolproof, but are a necessary component for medical device risk mitigation.

Some people believe that warnings are useless; printed on medical devices only to offer legal protection. Indeed, manufacturers can and have been held liable for the “failure to warn,” and adding warnings neutralizes this claim.

Some warnings offer some protection against some hazards some of the time. How’s that for making a conditional statement? In other words, there is value in warnings but they should not be seen as a panacea. They are one among many possible risk mitigations and not usually a substitute for designing a medical device to be inherently safe.

The importance of signal words

Recognizing the limited value of any particular warning, it makes sense to create the best ones possible. With this goal in mind, there is a lot to designing a good warning.

Following warning design conventions is a must. One convention is to draw attention to a warning using a signal word. The primary options are “DANGER,” “WARNING,” and “CAUTION.” The choice of signal word depends on the likelihood that someone could be harmed and the severity of the harm. “DANGER” indicates a hazard that will kill you in the event of exposure to it. “WARNING” indicates that a hazard might severely injure or kill you in the event of exposure to it. And finally, “CAUTION” indicates a chance of slight to moderate harm. Most people might not know the signal word hierarchy per se, but should get the point.

In addition to attracting attention using a signal word, it is conventional to state the hazard (e.g., “High voltage”) or safety objective (“Prevent burns”) and either prohibit a behavior (e.g., “Do not remove panel”) or encourage safe behavior (e.g., “Keep hands away”).

By convention, text-based warnings are often complemented by an informative graphic, which may indicate the hazard (e.g., laser light), the consequence of exposure to the hazard (e.g., fingers caught in moving parts), or the safe behavior (e.g., wearing protective eyewear).

Communication, design considerations

It is difficult to determine with any certainty whether or not a warning will deter unsafe behavior or promote safe behavior. However, it is possible to determine if a warning effectively communicates the intended message. For example, you can ask people to interpret graphics at-a-glance and have people read and interpret warning text. These means of evaluation can help designers refine warnings and, ultimately, avoid miscommunication.

Thereafter, the challenge is to place the warning where it will get noticed when the message is pertinent, which is usually in the user’s expected line of sight when (1) the chance of exposure to the associated hazard is greatest and (2) cautionary behavior is necessary. But, putting a warning in the theoretically ideal spot can create tension with device development team members concerned with medical device aesthetics and not “scaring the users.” Dealing with the possible tension and prevailing by placing the warning where it belongs depends on the warning designer’s diplomatic skills and empowerment. Mentioning the importance of protecting users from harm and giving the manufacturer legal claim of due care can also help the effective warning advocate prevail.

In closing, keep in mind that some warnings offer some protection against some hazards some of the time. That explains why nobody is in the water at beaches with a posted warning stating that sharks have been sighted. Read more about medical device design an usability on the UL Wiklund website

Michael Wiklund is General Manager of Human Factors Engineering at UL.

Related medical device regulatory resources

  • Human Factors Engineering (HFE) and usability testing support
  • Medical device design, process and software validation support
  • ISO 14971 risk management consulting



  • Michael Wiklund