Model Rocket Safety Code — A Dialogue

© NAR August 2012; 2021 edit and commentary by W.R. Portnell

 

I am a big fan of the Model Rocket Safety Code. I'm such a fan, I'm going to devote a page of my website to it and what I think about it. I have made a few changes in this rendering of the Code, to make the presentation of measurements consistent. I have also changed the ordering of the statements, to make what seems to me a better narrative. Indications of my changes are italicized.

1. Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.

Why lightweight and non-metal? There are two great reasons to have light rockets. First, they fly more more readily. You don't need big motors. Second, they can't carry enough momentum to do injury or damage if they go wrong. Per Mythbusters, a penny dropped from the top of the Empire State Building will not kill you. It's just too small, it can't carry enough kinetic energy. Same deal for model rockets.

2. Motors. I will use only certified, commercially-made model rocket motors, and will not tamper with these motors or use them for any purposes except those recommended by the manufacturer.

I loved the Mythbusters, but I cried inside every time they used model rocket motors for experiments not actually using rockets.
There's also another gotcha in this code: The manufacturer recommendations. I know, for instance, that some of my models should fly perfectly well on motors not recommended by the kit manufacturer. (This usually means motors from some other manufacturer.) But in a mishap it could be claimed I've violated this code and so not deserve my insurance protection. For me, this is just another reason to fly small with models that are nearly impossible to do harm with.

3. Size. (originally 7) My model rocket will not weigh more than 1,500 grams (53 ounces) at liftoff and will not contain more than 125 grams (4.4 ounces) of propellant or 320 Newton-seconds (71.9 pound-seconds) of total impulse.

When I started flying, liftoff mass was capped at 453 g (1 pound), although the propellant limit was nearly the same. Whoosh!

4. Launcher. (originally 6) I will launch my rocket from a launch rod, tower, or rail that is pointed to within 30 degrees of the vertical to ensure that the rocket flies nearly straight up, and I will use a blast deflector to prevent the motor’s exhaust from hitting the ground. To prevent accidental eye injury, I will place launchers so that the end of the launch rod is above eye level or will cap the end of the rod when it is not in use.

I find launch rod caps a fussy bit of business. But my launch system has a detachable controller. I think I'll a) make a cap out of a spent motor, paint it orange, and then b) attach the cap to the controller.

5. Ignition System. (originally 3) I will launch my rockets with an electrical launch system and electrical motor starters (igniters). My launch system will have a safety interlock in series with the launch switch, and will use a launch switch that returns to the “off” position when released.

"Igniter" is apparently a term of law associated with explosives. To avoid that association, we've been calling them "starters" since 2013. Us old-timers have a hard time adapting.

6. Launch Safety. (originally 5) I will use a countdown before launch, and will ensure that everyone is paying attention and is a safe distance of at least 4.5 meters (15 feet) away when I launch rockets with 30 Newton-seconds of total impulse (D motors) or smaller, and 9 meters (30 feet) when I launch larger rockets. If I am uncertain about the safety or stability of an untested rocket, I will check the stability before flight and will fly it only after warning spectators and clearing them away to a safe distance. When conducting a simultaneous launch of more than ten rockets I will observe a safe distance of 1.5 times the maximum expected altitude of any launched rocket.

"Maximum expected altitude" means you've got to know that value, either by mathing, computing, or manufacturer data for the kit. Stability can be tricky, and while most manufacturer kits are reliable, it never hurts to check them out, either with software or with a quick string test.
The 30 N-s line for minimum safe distance comes from NFPA 1122. The D motor limit is easier to explain and conservative.

7. Launch Site. (originally 9) I will launch my rocket outdoors, in an open area at least as large as shown in the accompanying table, and in safe weather conditions with wind speeds no greater than 9 meters per second (20 miles per hour). I will ensure that there is no dry grass close to the launch pad, and that the launch site does not present risk of grass fires.

Installed Total
Impulse (Newton-seconds)
Equivalent
Motor Type
Minimum Site
Dimension in meters (ft.)
0.00 - 1.25Micro, MMX, ¼A, ½A15 (50)
1.26 - 2.50A30 (100)
2.51 - 5.00B61 (200)
5.01 - 10.00C122 (400)
10.01 - 20.00D152 (500)
20.01 - 40.00E305 (1,000)
40.01 - 80.00F305 (1,000)
80.01 - 160.00G305 (1,000)
160.01 - 320.00Two G457 (1,500)
Site dimension is diameter of circular site or shortest side of rectangular site.
NFPA 1122 Code for Model Rockets now allows a minimum site dimension of one-half the maximum expected altitude based on software predictions. The above table reflects a minimum site dimension of one-quarter the maximum expected altitude. "Expected altitude" still means you have to have done the math.
Grass fires are the pernicious arch-foe of the rocketeer. The best way to not have grass fires is to not fly near grass. But grass makes such a wonderfully forgiving landing surface. I don't fly near grass or brush, but that means I have to be sure my recovery speeds (below) are very gentle indeed.

7. Flight Safety. (originally 8) I will not launch my rocket at targets, into clouds, or near airplanes, and will not put any flammable or explosive payload in my rocket.

Self-explanatory, really.

8. Misfires. (originally 4) If my rocket does not launch when I press the button of my electrical launch system, I will remove the launcher’s safety interlock or disconnect its battery, and will wait 60 seconds after the last launch attempt before allowing anyone to approach the rocket.

An interlock is defined as a piece of the circuit that can be physically removed from the circuit. This is the safety key of the launch system. Many launch controllers use a key-switch that returns to the off position. I'm not in favor, but I haven't seen a lot of issues with these. In my self-designed launch system, the controller grip itself is the safety key.

10. Recovery System. I will use a recovery system such as a streamer or parachute in my rocket so that it returns safely and undamaged and can be flown again, and I will use only flame-resistant or fireproof recovery system wadding in my rocket.

Recovered and able to fly again is really, really important to me.

11. Recovery Safety. I will not attempt to recover my rocket from power lines, tall trees, or other dangerous places.

The easiest way to not have these problems is to choose not to fly near power lines, tall trees, or other dangerous places. Finding a launch site of the right size and character is hard!