Critical incident debriefing is an occupational health tool for supporting healthcare workers following critical incidents. Demand for debriefing has increased following the Covid-19 pandemic. There is now a need for more trained debrief facilitators to meet demand, but there is a dearth of literature regarding how best to train facilitators. This study addressed this by exploring participant experiences of an online critical incident debrief training programme. We conducted semi-structured interviews with 14 individuals who received a 5-day training programme based on the Critical Incident Stress Management model. Participants were recruited from a range of professional disciplines including psychology, nursing and human resources within one British healthcare system. Data were analysed using thematic analysis. The analysis produced three themes. Managing trainee experiences and expectations suggested that disciplinary heterogeneity in training groups supported inter-participant knowledge exchange. However, this variation also meant that training materials did not meet the learning needs of all participants. Modality of training suggested that while online learning was acceptable for some, others experienced screen fatigue and found it hard to build rapport with other participants. Systematic and organisational obstacles to training access and delivery suggested that lack of managerial support and organisational mental health stigma may be barriers to accessing training. A 5-day online CISM-based training programme was acceptable to participants. Organisations implementing critical incident debrief training may benefit from (1) offering both in-person and online training options, and (2) tailoring course materials according to the disciplinary make-up of groups.