What is an event chain diagram and how is it used?

• A. A diagram that maps the layout of equipment in a facility.
• B. A modeling tool that shows sequences of events after a hazard occurs and identifies critical failure paths and barrier effectiveness.
• C. A schedule for maintenance tasks.
• D. A statistical model of market risks.

Answer: (B)

An event chain diagram captures how a hazard can unfold by laying out the initiating event, the sequence of follow-on events, and where safety barriers may stop or fail to stop progression. It’s time-ordered and can branch when different conditions change the path, so you can see multiple potential outcomes from one initiating situation. This helps identify critical failure paths—the sequences of events that lead to a consequence—and it shows barrier effectiveness by illustrating whether safeguards would interrupt the chain or, if they fail, allow it to continue. In practice, you use it to visualize accident scenarios during risk assessment, pinpoint vulnerable spots where controls are weak, guide where to strengthen safeguards, and communicate how risks could propagate to leaders and operators. It’s not simply a diagram of equipment layout, a maintenance schedule, or a statistical model of market risks, which don’t describe how hazards propagate through a system or how barriers perform in sequence. For example, you might map how a leak could lead to vapor spread and ignition, with detectors, ventilation, and automatic shutdowns affecting whether the chain continues or is halted.