Over my career I have seen many firefighter injuries...some on-duty injuries and some off-duty injuries. The most regrettable injuries are those that are preventable, and even more so, those that occur as part of one's fitness program.
It is obviously counterproductive to incur any injury during your fitness training. The whole point is to increase your career longevity, performance and overall health and well-being, but too often we have a tendency to overdo it and as a result can end up doing more harm than good.
You can still get results with less risk. Utilizing proper form and technique is of utmost importance. Educating yourself in proper techniques and knowing your own body's limits is imperative. Keep this fact this in the front of your mind while training by reminding yourself how awful it would be to incur a life-long injury due to your fitness program.
There are typically one of three laws of physics at work that lead to a training injury; compression, leverage and torque. Being mindful of these laws and how they are impacting your anatomy while training will help in injury prevention and help you to "do no harm."