A series of emails about taking CO₂ tyre-inflators on our flights next month…

1. From me to the airline:
   

   I’ve just thought of another potential problem to do with carrying bikes on aeroplane. When cycling in the UK, we tend to carry containers of CO2 – they reinflate tyres much more quickly than using a manual pump. You can see a description here. Is it OK to take these in our hold luggage?

2. Their reply:
   

   Dear Mr Bruce,
   Thank you for contacting us. With reference to your e mail I would like to confirm that you will be allowed to carry empty containers of CO2 in your hold luggage as long as it fits in the hold baggage dimension of 275cm (length+width+height).
   CO2 is a highly inflammable substance which is strictly prohibited on board.
   Yours sincerely
   [name]
   [airline] Customer Services

3. My response:
   

   Dear [name]
   Thank you for your email. However, it is somewhat puzzling. You say I can carry empty containers in hold luggage, but then that CO2 is ‘highly inflammable’ and ‘strictly prohibited on board’. I assume that ‘on board’ means ‘anywhere on the aircraft’.
   Firstly, there would be no point in carrying empty containers.
   Secondly, CO2 is does not burn under any circumstances. It is commonly used in fire extinguishers because it is inert and absorbs a great deal of heat. During my chemistry PhD, I occasionally ran reactions under a CO2 ‘atmosphere’ to prevent the oxidation (burning) by the oxygen in normal air.
   I do understand that CO2 containers might be dangerous because they are pressurised. I presume this is why they are forbidden in cabin luggage.
   However, they appear to be permitted in hold luggage according to CAA regulations. Please see the top row of the table here.
   So am I allowed to take CAA-approved CO2 containers in hold luggage on your flights?
   Many thanks
   Dr Bruce Ryan

Sometimes my PhD seems worthwhile!

4. The final word
   

   Dear Mr. Bruce,
   Thank you for contacting us.
   I apologise for the incorrect information provided to you in the previous e-mail. Having discussed with my supervisor I can confirm that you will not be allowed to carry CO2 containers either on board or in the hold.
   Sorry for the inconvenience caused to you.
   Yours sincerely
   [name]
   [airline] Customer Services