We’re not talking model rockets here. These are big, serious rockets.
There are two main rocketry organizations in the US: the National Association of Rocketry (NAR), and the Tripoli Rocketry Association (TRA). NAR supports amateur rocketry in all its facets, including model rocketry – the Estes kits many of us built as kids. Tripoli is solely focused on high-power rocketry – rockets capable of apogees of a couple thousand to hundreds of thousands of feet. Tripoli also allows experimental motors and engines, something not allowed under NAR rules.
Both organizations administer certification programs for high-power rocketry, and they recognize each others’ certifications. A person must be certified to purchase high-power rocket motors and to launch rockets with those motors. Both organizations make training and safety the highest priority. Amateur rocketry is a very safe hobby because of that focus on safety.