Operating Pressure Validation

Results Discussion Conclusion	Aim To validate 100 PSI as a safe operating pressure for 600 ml PET Coke bottles. To asses the durability of the 600 ml PET Coke bottles under simulated field conditions.
	Method [1] 600 ml PET Coke bottles were pressurised until they either contained 150 PSI or exploded. This test was repeated for 20 bottles. [2] 600 ml PET Coke bottles were crushed flat by being stepped on. They were then pressurised until they either contained 150 PSI or exploded. This test was repeated for 20 bottles [3] 600 ml PET Coke bottles were pressurised to 100 PSI. The pressurised bottles were used singly to support one end of a bridge composed of a hardwood beam resting with its second end on a brick. A person weighing 100 kg (220 lb) then jumped onto the beam from a height of 64 cm (25 in). This test was repeated for 20 bottles.

Aim / Method Discussion Conclusion	Results [1] All 20 bottles contained 150 PSI without exploding. [2] 6 of the bottles were damaged by being stepped on to the point that they could not hold pressure at all. In all cases the damage occurred as a crack in the thickest section of plastic in the center of the end of the bottles. The remaining 14 bottles contained 150 PSI without exploding. [3] All 20 bottles withstood being jumped on without exploding.

	A short MPEG clip showing an example of the third trial can be downloaded by clicking on the still below.
	Corin Anderson in mid air as he puts the 600 ml PET Coke bottles through their paces

Aim / Method Results Conclusion	Discussion It is generally accepted in engineering design that for most purposes a 50% safety margin is acceptable. With that in mind the first trial was designed to test whether 600 ml PET Coke bottles could provide a 50% safety margin over a 100 PSI operating pressure. The fact that all of the bottles in the first trial successfully contained 150 PSI would indicate that an operating pressure of 100 PSI would allow at least a 50% safety margin. The likelihood of water rockets that have been fired into a unit heavy fighters being stepped on is quite high. The second trial was designed to address what effect being crushed underfoot has on the bottles ability to hold pressure. The pattern of failure that emerged from the trial was very regular. Damage that led to a pressure leak always occurred as a crack in the center of the base of the bottle where the plastic is thickest and presumably most brittle. Damage occured in a critical fashion i.e. the bottles either completely failed to hold pressure through cracking or were able to hold 150 PSI.     Crushed bottle with crack Crushed bottle without crack The third trial was designed to see what would happened in the event of a fighter accidentally stepping or falling onto a pressurised bottle. It should be pointed out that any potential danger this presents only exists while the bottles are pressurized and therefore either loaded into cannons or in the process of being loaded. The height from which the bottles were jumped on (two milk crates) was chosen as being sufficient for generating a greater force than would be imparted by a fighter stepping or stumbling onto a pressurised bottle. In a different experiment a longer bridge than the one used in the third trial was set up to try and find the greatest static load a bottle pressurised to 100 PSI could withstand. After loading the bridge with over 450 kgs (990 lb) worth of people to no effect the experiment was abandoned.     600 ml Coke bottle at 100 PSI holds up the 450 kg (990 lb) weight of these four likely lads

	Conclusion The 600 ml PET Coke bottles tested in this trial are capable of be used at a pressure of 100 PSI while still providing a safety margin of at least 50%. The kind of crushing damage that is likely to be experienced by a bottle during combat results in either no effective damage or complete failure of the bottle to hold pressure. The impact that can be regularly sustained by a 600 ml PET Coke bottle pressurized to 100 PSI is greater that what could conceivably occur as the result of being accidentally stepped or fallen on during combat.

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