I learned a new lesson today.
On the NEPN around 8:05am, roughly at Ainslie Park Leisure Centre, I spotted a lady walking with her bike, so stopped to ask if she was ok. She had a flat. Her bike looked like some kind of hybrid, but her wheels looked around the same size as my road wheels so I offered to stick in one of my tubes to get her on her way.
I did this, and after pumping up the tube with the C02 canister, the tyre didn't look properly inflated, and after 5 seconds, the tube inside exploded. Odd, I thought. So I took it out, checked there was nothing sharp inside the tyre, and tried again with my other spare tube.
This time, I had to use my pump, and while trying to pump it up, realised the same thing was happening, so stopped, let the air out again and then realised my fail - the tyre was much wider / deeper, so although the circumference of the wheel was the same as my tyre, the tube needed to be much bigger, and thus my tube had exploded because it had attempted to fill a space much bigger than what it was designed for. Oops. Lesson learned.
I then did what I should have done in the first place, which was to find the hole in her tube and stick a patch on it to get her back home. Job done.
Two other people stopped to ask if assistance was needed, so if any of those people are on here, thanks for the offer.