In theory, no one should ever be injured or killed during fire service training exercises. Training, by definition, should take place in a controlled environment, with specific goals, objectives and outcomes.
Of course, this is a fallacy. Training fires are still fires. Creating training scenarios that mimic actual fire response will necessitate also including some of the risk associated with emergency response.
According to data gathered by the NFPA, line of duty deaths resulting from training events made up an average of 8.5 percent of firefighter lives lost between the years 1977 and 2015. This is a significant number.