Model rockets are relatively safe when compared to similar activities such as flying model airplanes. A box of model rocket engines is considerably less flammable than a similar sized can of model airplane fuel. While model rockets move fast, they do not move anywhere near as fast as the tip of the propeller of a model airplane. While the risk is not large it is possible to hurt yourself with a model rocket if you are not careful.
The greatest risk from model rockets is a high-speed, human-rocket collision. Even if a rocket weighs only a few ounces, it is going to do some damage if it hits you at 200 miles per hour. If you are traveling at 200 miles per hour and manage to hit a stationary model rocket, we will cart you off to the hospital, refund your membership dues, and ask you to not return. There is just so much we can do for you and we would prefer to not have you around breaking up our rockets. On the other hand, we will do our best to prevent a fast moving rocket from hitting you, but we do need your help. You must pay attention while a rocket is in the air and you must follow the NAR safety codes.
There are two situations where you are at risk of being hit by a high-speed, model rocket: during boost phase and during recovery. Human-rocket interactions during boost phase are very rare because any rocket failures are localized to the area of the pad and the rocket is directed in the upward direction using a launch wire. Both of these things tend to keep the rockets away from the spectators during the boost phase. This does not mean that there are no failures during the initial boost, only that they are relatively rare. The most common causes for initial boost failures involve underpowered rockets, partial engine failures and inopportune gusts of wind. All three of these causes can result in a rocket flying horizontally instead of vertically. To protect yourself from these flights, pay attention during launch and be prepared to duck and cover if a lawn shark heads in your direction.
The second situation where you might be hit by a high speed model rocket is where the rocket's recovery system has failed and the rocket is returning to the earth in a ballistic configuration. This can happen if the engine ejects from the rocket instead of deploying a parachute or streamer, or if a second stage engine fails to ignite (or ignites late). A rocket returning from a high altitude in a ballistic configuration can reach very high speeds. If a slow second stage engine finally starts to burn after the rocket has started for the ground, it can get moving even faster. Again, the best protection is to pay attention during the launch so that a lawn dart does not drop in on you unannounced.
Fire from model rockets is generally not a problem as the fuel is completely burned in a few seconds, leaving only a slightly hot paper engine casing. On the other hand, if you ignite an engine while holding it in your hand it is definitely going to hurt. It is also not an allowed model rocket configuration as you most likely weigh more than the 53 ounce maximum. Explosions from model rockets are also not a problem as the paper engines are designed to blow out their end plugs before dangerous explosive pressures are reached.
If you use common sense, pay attention, and follow the NAR safety code you will be able to have many successful flights without sustaining any injuries. Safety is the hallmark of a good model rocket program and is scrupulously practiced by LUNAR.