PurposeThe purpose of this paper is to explore how a number of processes joined to create the microlevel strategies and procedures that resulted in the most lethal and tragic forest fire in Portugal's history, recalled as the EN236-1 road tragedy in the fire of Pedrógão Grande.Design/methodology/approachUsing an inductive theory development approach, the authors consider how the urgency and scale of perceived danger coupled with failures of system-wide communication led fire teams to improvise repeatedly.FindingsThe paper shows how structure collapse led teams to use only local information prompting acts of improvisational myopia, in the particular shape of corrosive myopia, and how a form of incidental improvisation led to catastrophic results.Practical implicationsThe research offers insights into the dangers of improvisation arising from corrosive myopia, identifying ways to minimize them with the development of improvisation practices that allow for the creation of new patterns of action. The implications for managing surprise through improvisation extend to risk contexts beyond wildfires.Originality/valueThe paper stands out for showing the impact of improvisational myopia, especially in its corrosive form, which stands in stark contrast to the central role of attention to the local context highlighted in previous research on improvisation. At the same time, by exploring the effects of incidental improvisation, it also departs from the agentic conception of improvisation widely discussed in the improvisation literature.