Learning by Accident

««« Submitted by a STAO member, Region 2

Learning by Accident is an ongoing Crucible feature, in which real-life lab accidents or incidents are recounted and explained. The goal is to highlight the consequence of ignoring safety rules so that science educators will be further encouraged to become knowledgeable, and to take appropriate action, in areas of safety that affect their daily activities in the science classroom. Submissions are encouraged. Anonymity will be guaranteed. Please send written descriptions to Ian Mackellar, STAO Safety Committee Past-Chair, Box 191, MAITLAND, ON K0E 1P0

Accident with a Plastic Pop Bottle Rocket

I had just finished pumping up the internal pop bottle rocket pressure to 70 psi with a bicycle pump. I was doing this with my back to the launcher on which the rocket was angled at 45 directly away from me. As I bent down to put down the pump, the bottle exploded and blew off the nose cone (made from the cap end of another bottle). The nose cone somehow flew back and hit me in the mouth resulting in a nasty cut requiring immediate hospital treatment, much pain, a permanent facial scar and thousands of dollars in dental work.

Comments from the STAO Safety Committee
Before any projectile is launched outdoors, including a water rocket, the teacher should always pretest a similar projectile to determine the path it will follow and its range as well as the amount of variability to be expected. Students should be kept clear of the path and impact area and made aware of the potential hazards.

More specifically, the STAO member reporting this accident – who has demonstrated the flight of pop bottle rockets numerous times without incident prior to this unfortunate accident – highly recommends that:

“Teacher demonstrators should:
1. Wear safety glasses and a full face shield OR safety glasses and a hockey helmet with face guard.

2. Use only NEW plastic pop bottles i.e., bottles whose soft drink contents have recently been consumed.

3. Make ALL adjustments to the rocket BEFORE any air is pumped in.

4. If streamlining the water rocket with a nose cone, then ensure that the nose cone is NOT sharp¬pointed or metallic. (Any modifi¬cations, including attachment of fins, should not be done with a hot glue gun as this could compromise the integrity of the bottle.)

5. If the launcher has a locking mechanism, ensure that the internal pressure of the pop bottle rocket does NOT exceed 90 psi max. by using a bicycle pump that has a pressure gauge incorporated. (A compressor should NOT be used because it could create excessively high internal pressure, increasing the danger of the bottle exploding or being propelled beyond a safe distance.)

6. Attach the bicycle pump to the bottle rocket using a long hose at least 3 m in length. (For launchers having a U-bolt locking mechanism, use a release string about 3 m long also to ensure that a safe distance from the launch site is assured. Further, a second shorter string approximately 1 m in length should be attached from the U-bolt to the eyelet to stop the U-bolt from flying back too far.)

7. Keep a clear area about 100 m downrange, about the length of a soccer field, just in case a perfect rocket is made. (They have gone over 80 m with 70 psi.)

8. Launch pop bottle rockets well away from hydro lines and electrical sub-stations. (Buildings and roads may also present hazards.)

9. If at any time there is a problem with the launch, approach care¬fully with a shield (e.g., garbage can lid) and a broom handle to knock the rocket off the launcher, away from you and the students. This should cause it to release.

Students should:
1. Be at least 30 m away from the launch site, with a suitable mark (e.g., asphalt parking lot/edge of grass, a track curb, soccer posts etc) to stay behind as they get excited and tend to creep closer and closer. (A water source could be placed here for filling the bottles.)
2. Be upwind of the launch. This is especially important when doing a vertical launch.”

The STAO Safety Committee strongly supports these recommendations and again reminds teachers that ALL investigations involving the launching of water rockets should involve teacher demonstration ONLY. These activities are too hazardous for students to be allowed to perform.

SAFETY CAUTION!! Other incidences of accidents involving pop bottle rockets have recently been reported, further emphasizing that this is a potentially hazardous activity requiring extra precaution by teachers who still decide to perform this activity.