The release of a hazard is the first undesired event. This event is called the Top Event (the first Hazardous Event.) The Top Event is at the end of the fault tree and at the beginning of an event tree.
Other Related Terms and Definitions:
ISO-17776 – Particular hazardous event considered in the development of fault and event trees.
Source: International Association of Drilling Contractors, Appendix 2 to Health, Safety and Environment Case Guidelines for Offshore Drilling Contractors, Issue 3.3.2, February 2010. IADC Guidelines
Particular hazardous event considered in the development of fault and event trees.
Source: ISO 17776:2000, Petroleum and natural gas industries – Offshore production installations – Guidelines on tools and techniques for hazard identification and risk assessment. Global Standards