Risk Assessment

Method Results Discussion Conclusion	Aim To answer the following questions about 600 ml PET Coke bottles: 1. Can the bottles contain a pressure of 150 PSI. 2. What kind impact can a bottle pressurized to 120 PSI sustain without rupturing. 3. What force is exerted by the explosion of a bottle pressurized to 120 PSI on a nearby object. 4. Would a layer of cloth provide protection from fragments ejected by a bottle during an explosion.
Aim Results Discussion Conclusion	Method
	1. Can the bottles contain a pressure of 150 PSI. 600 ml plastic Coca Cola bottles were pressurized with an electric compressor to 150 PSI. Any explosions were noted. 2. What impact force can a bottle pressurized to 120 PSI sustain without rupturing. 600 ml plastic Coca Cola bottles were pressurized to 120 PSI. A combination of dumbbell weights weighing 2.2, 4.4, 6.6, 8.8, 11, 13.2 kg (5, 10, 15, 20, 25 and 30 lbs) were dropped on the bottles in sequence from a height of 1 meter (3 ft) until the bottles either exploded or survived the final 13.2 kg impact. The impacts survived by each bottle were noted. 3. What force is exerted on an object by the nearby explosion of a bottle pressurized to 120 PSI. The pendulum used in the impact tests was set up so that the center of the target face was 30 cm (1 ft) from the end of the bottles. The deflection of the pendulum caused by any bottles that exploded was noted. 4. Would a layer of cloth provide protection from fragments ejected by a bottle during an explosion The target face was covered in a single layer of calico. At the end of the trial it was examined for signs of any damage.
	Click on the stills below to download short MPEGS of two of the trials (881 KB / 681 KB)
	13.2 kg (30 lb) of dumbbell weights bounces off a bottle pressurized to 120 PSI	A bottle explodes on impact with 13.2 kg of dumbbell weights. The pendulum is displaced 12 cm
	Notes The pendulum built for the impact tests was used in this trial. The only modification involved lowering the height of the pendulums supporting bar. Star pickets were used to provided a standard position for dropping the weights and to prevent the weights from bouncing into the pendulum. The bottles were raised from the ground using a block of wood placed on two bricks.

Aim Method Discussion Conclusion	Results All of the 10 bottles in the trial successfully contained 150 PSI. There were no explosions. The results of parts 2 & 3 of the trial are listed below. A bounce is represented by the letter B and an explosion by the letter X. The deflection of the pendulum caused by each explosion is listed. Bottle 5 lb 10 lb 15 lb 20 lb 25 lb 30 lb Deflection(cm) 1 B B B B B B   2 B B B X     10 3 B B B B B X 12 4 B B B B B B   5 B B B B X   11 6 B B B B B X 11 7 B B B B X   10 8 B B B B B B   9 B B B B B B   10 B B B B B X 11 After the six explosions in the trial the calico square was examined and found to be completely undamaged.

Aim Method Results Conclusion	Discussion Most of the difficulty we experienced in conducting this trial is related to the extremely robust nature of the plastic bottles. We had initially planned to determine the pressure at which the bottles exploded but were balked when the hose on our hand pump failed at around 135 PSI. We then purchased an inexpensive electric compressor which was supposedly rated to 250 PSI but could only consistently manage to pressurize the bottles to 150 PSI. This has limited us to demonstrating that the bottles can contain 150 PSI without exploding. In our previous use of the water rocket cannons we have set ourselves an operational limit of 100 PSI. The demonstrated capacity of 150 PSI provides a 50% margin for safety. Pump and Compressor used in the trials Our experience of pumping up the bottles with a hand pump has aquainted us with the physical difficulty involved in reaching even 100 PSI. By the time we had reached 135 PSI the effort involved was extreme. It is our belief that it would be impossible to accidentally pressurize one of the bottles to a dangerous level with a hand pump because the exertion required would serve to alert you if your pressure gauge had failed. The robust nature of the bottles again presented itself when we initially tried to cause them to explode by dropping weights on them. At 100 PSI the bottles were almost impossible to rupture even with the 13.2 kg (30 lb) weights. The final trial was carried out at 120 PSI to provide a greater chance that the bottles would explode and as such represents a more extreme situation than what we would consider normal for SCA field use (i.e. 100 PSI limit). Even at 120 PSI the bottles proved quite resilient with four of them surviving the trial intact. In a less formal test one of us (Corin) both stood and jumped on a bottle pressurized to 100 PSI. After around 20 jumps the bottle still had not ruptured.
	Click on the stills below to download short MPEGS of the jump test (586 KB / 381 KB)
	Corin stands on a bottle with his 100 kg (220 lb) weight	Corin jumps on a bottle with his 100 kg (220 lb) weight
	The deflection on the pendulum caused by the force of the explosions averaged to 10.8 cm (4.3 in) which is only 63% of the average deflection caused by the arrows in the impact tests. To put this further into perspective, the arrows transfer their force to the pendulum through an impact area of 3.1 sq cm (0.5 sq in). Assuming the force of an explosion shockwave is captured across an area equvialent to the 7 cm (2.8 in) diameter of the bottle (and it is almost certainly spread over a larger area) the average force applied by the explosions to an area of 3.1 sq cm would equal roughly 1.3% of the force applied by an arrow. In this, and previous experiments, we have exploded nearly 30 bottles by dropping weights onto them at pressures ranging between 100 and 150 PSI. In every instance the bottles have ruptured at the base and ejected fragments of plastic a few feet in the direction pointed by the end of the bottle. The resistance of the calico to the shrapnel produced in the trials suggests that normal clothing would provide adequate protection. Example of ruptured bottle showing typical failure pattern The possibility of eye damage resulting from the shrapnel could be eliminated by ensuring that all bottles are contained in a barrel or breechblock. In the demonstrably unlikely event of a rupture the path of the shrapnel would be constrained by the barrel or breechblock. Eye damage could then only result if an individual deliberately looked down the barrel of the cannon or breechblock.

Aim Method Results Discussion	Conclusion The 600 ml PET Coke bottles used in this trial can safely contain a pressure of 100 PSI. While pressurized they are able to withstand rough handling to the extent of being dropped, stood or jumped on without rupturing. Deliberate action is required to cause a rupture to occur at 100 PSI. When the bottles do rupture they do so in a predictable manner. The force released during a rupture is minimal and of a safe level, adequate protection being offered by normal clothing.

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