The Ladder

Type	What happens	Tests
Seminar / workshop	Familiarisation and discussion of the plan	Understanding; identifies obvious gaps cheaply
Tabletop	Team talks through a scenario around a table	Decision making, roles, interfaces, assumptions
Drill	One procedure practised for real — evacuation, muster, call-out, spill kit deployment	Mechanics and timing of a single activity
Functional exercise	Command teams respond in real time to injects, without deploying resources	Communications, escalation, information flow, command
Full-scale exercise	Live deployment with casualties, equipment and often emergency services	The whole system end to end, including the friction

Building a programme

Escalate over time. A full-scale exercise run before the tabletop has exposed the obvious problems simply demonstrates those problems expensively, and tends to demoralise the participants. A sensible annual programme has frequent drills, regular tabletops, at least one functional exercise, and a full-scale exercise at a longer interval.

Include the interfaces

Test with the parties you will actually rely on: emergency services, mutual aid partners, neighbouring sites, corporate crisis teams and contractors. Interface failures — incompatible radios, different terminology, unclear command handover — are only found when the interface is exercised.