Speaking at the IP EXPO Europe exhibition in London’s Royal Victoria, he announced details of a leak that struck the ISS in 2013.
On May 10, 2013, the ISS astronauts noticed “firework-like” sparks flying outside the windows of the space laboratory.
Colonel Hadfield said the sparks were small amounts of liquid ammonia seeping out from the space station’s cooling systems.
The leak, undetectable at first, had the potential to wipe out the ISS’ batteries and force some, if not all six astronauts onboard, to “abandon the ship”.
The revelation comes less than a month after NASA officials were alerted to an oxygen leak onboard the ISS.
Mr Hadfield told Express.co.uk the ammonia leak could have been the end of their mission above Earth.
The veteran astronaut said he was alerted to the problem by Russian cosmonaut Pavel Vinogradov who saw “fireworks, or sparks or something” coming out of the side of the spacecraft.
He said: “We talked down to Houston and they, of course, haven’t seen anything yet.
“We looked at our own data and you couldn’t see a pressure drop yet because it is a pretty reasonable reservoir of ammonia, but we looked at it closely and started to get ready for spacewalks.
“After a while, the pressure dropped enough to start diagnosing exactly and depressurise.”
What followed was a “busy, busy day” of trying to carry out a spacewalk in a very limited amount to time.
He said: “You never do a spacewalk just off the cuff – they’re dangerous, and hard, and have to be choreographed and everything practised.
“It normally takes eight days to prepare a spacewalk. We did a spacewalk in one day, or maybe 30 hours.
“It was crazy busy – a wild day.”
The dire rescue mission was undertaken by NASA astronauts Chris Cassidy and Tom Marshburn, who helped build the damaged section of the ISS years before.
As a result of fighting against his spacesuit’s pressurisation, Mr Marshburn returned to the ISS with nerve damage in both his hands.
Mr Hadfield likened the struggle of the repair effort to sticking your hand into a very uncomfortable position and working it for six hours straight without a break.
He said Mr Marshburn’s hands were “numbs for months after that”.
The astronaut said: “They removed the leaking section and got a little ammonia on them, which is nasty stuff.
“We don’t want to bring any ammonia into the ship, because we’re in a closed bubble.”
The piece of the space station removed from the ISS was about the size of a refrigerator.
It was a “huge, cumbersome” piece of equipment, likely designed decades prior.
Mr Hadfield said: “All machines fail. I grew up on a farm. All machines fail – you have to accept that like all people die.
“Don’t pretend it’s not true, just accept that, and it’s how long you keep that machine working is all that matters.
“If we had lost that, then we couldn’t have cooled batteries, we couldn’t cool the inside of the ship – at least some of us would have had to abandon ship, if not all of us.
“And that wouldn’t have fixed the problem, you know. Someone’s going to have go up there and fix.
“Fortunately the six of us, between us, had an awful lot of preparation and everyone was spacewalk qualified, which is not trivial.”