What is a STEP chart?
A STEP (Sequentially Timed Events Plotting) chart maps each actor's actions on a horizontal timeline, exposing convergence points where multiple actors interact. It is essential for multi-party incidents like vessel collisions or process upsets.
Developed by Kingston in the 1980s for transport accidents, STEP charts solve the problem narrative reports cannot: showing who did what, in parallel, at exactly which second. Multi-actor incidents — bridge collisions, control-room handovers, simultaneous operations — become legible.
How it works
1. List actors
Identify every person, system or piece of equipment that took an action during the incident window.
2. Build the timeline axis
Choose granularity (seconds, minutes) and span. Anchor with reliable timestamps from logs or CCTV.
3. Place each event on its actor row
Each action becomes a node tied to its actor and exact time.
4. Draw causation links
Connect events that influenced each other across actors using arrows.
5. Highlight convergence and gaps
Mark moments where actors collided, miscommunicated or where information was missing.