Warnings briefing note: False alarms and near misses

This document investigates false alarms, defined as events that do not occur when a warning is issued, and near misses, defined as events without warnings that could have caused harm but did not. A case study on Hurricane Sandy is also included.

Guidance is provided in the management of false alarms and near misses:

• Define false alarms e.g. false alarm ratios and rates, for the warning system as part of the system's performance metrics.
• Use uncertainty information routinely in hazard warnings, communicated so that a wide variety of public can understand them.
• Enhance credibility and public engagement by explaining why near misses and false alarms occur.
• Tell the public what is not known about a possible threat as well as what is known and what might happen.