PIARC defines the term “incident” in the following way: An incident is an “abnormal and unplanned event (including accidents) adversely affecting tunnel operations and safety”.
This definition of “incident” is quite broad and includes all kinds of events that may occur in a road tunnel. From a safety perspective report 2016R35 “Experience with significant incidents in road tunnels” recommends a focus on significant incidents. According to the definition in this report, significant incidents are “incidents which require special attention, because they are, or have the potential to develop into, events with serious consequences to the health or life of people, to property, to infrastructure or to the environment; or are valuable for further evaluation with respect to underlying basic risk factors. Significant incidents in particular include collisions and fires, which are addressed separately in pages Collisions and Fires respectively; the release of dangerous goods (addressed in page Hazards due to DG-Transport) is another typical example for a significant incident. However, the definition of significant incidents differs from country to country; in some countries other incidents like vehicle breakdowns or incidents that cause the closure of a tunnel are also considered as significant.
The basic understanding of these terms is illustrated in Fig.1.