I travel yearly for cycling adventures from Aus to Italy. There is on-going conflict in the web pages about whether CO2 canisters are 1. safe or2. allowable. Checking with my Airline (Oman) luggage page had a Forbidden Items picture card which did not include canisters. Reading further into luggage details I found a comment that "gasses" were not allowable. There are however many online comments that 2 canisters are allowable for "personal use". I today (June 2018) passed through check in bag scan with 2 xCO2 canisters in my carry on luggage with no issue. I reasoned that the higher the ambient pressure the safer, and further that if they were seen and confiscatable, I would rather just give them to the scanning desk instead of having my checked luggage or bike bag opened in my absence.