The Helium shortage worried me at first so I did some reading. Some people talk about different grades of Helium (different purities such as Ultra High Pure, Medical Grade, Divers Helium, Welders Helium and, at the bottom of the rankings, Balloon Helium). However, reading posts by people who are in the gas business reveals that except for UHP and the very high grades, it's all the same stuff except on paper. Helium usually occurs in pockets of Natural Gas and is the product of radioactive decay. It is abundant in stars. The shortage seems to be the product of media panic, rising demand from emerging markets and the lack of exploration for new sources of helium. Countries which profit from their reserves are very aware that they are finite. A market with a rising price means that their finite stocks are worth more. By withholding information about the discovery of new pockets of gas the market price can be kept high with an imposed 'crisis'. Another consideration is that our pupils are between the ages of 15 and 18 I've got to make choices which carry the least risk. Helium is (relatively) safe to deal with. Hydrogen on the other hand is not, and would result in an insurance cost beyond our means. We were quoted £5000 for the two launches by a specialist insurer (using Helium) - thankfully our insurer covered us for free after a very comprehensive risk assessment. I don't want to know what they would charge if we were using Hydrogen. As we are beginners Helium seemed like the best choice but I am tempted to try Hydrogen - greater lift and cheaper cost - but it will depend on several other factors, especially insurance cost.