There aren't many of us who go to work each day knowing that one little mistake could mean certain death for our colleagues.

But when you wake up each morning in your workplace, and your workplace is the International Space Station, that's a near-constant concern.

Commander Chris Hadfield, one of Canada's most experienced astronauts, is training for a mission to the ISS, and is scheduled to travel there aboard a Russian Soyuz rocket later this year. His mission includes six months living on the ISS, including three as commander of the station.

A big part of his and every astronaut's training is what to do in a potential emergency. And there are quite a few of them.

"There's constantly the opportunity for you to do something that will kill everyone with one small inattention, or one small indiscretion, or if you're just a little bit careless," Hadfield said in a telephone interview from Texas.

"You don't want to dwell on it, you don't want to ever let it be uppermost in your thoughts. But it always has to be running in the background of your thoughts: ‘Okay, I'm going to do this now, and what is the impact? What does it do to the ship, what does it do to the environment, what does it do to my crew members, and is that all still okay?'"

Hadfield says it takes a minimum of two-and-a-half years of training to become fully qualified to deal with any potential emergency, be it while aboard a shuttle or rocket or while living and working aboard the ISS.

Half the risk of any mission is during launch and landing, he says, but problems can arise during everything from spacewalks to eating breakfast.

The biggest concerns during a stay on the ISS include loss of pressure (which can be caused by, among other things, a small meteorite hitting and piercing a hole in the station); fire (from an electrical short or a flammable liquid igniting); or a chemical leak.

But something as simple as running on a treadmill (the astronauts strap themselves down so they can get cardiovascular exercise) can have devastating consequences.

"It's a big, flexible balloon that you live in, and just running on the treadmill can cause the whole station to start to get into an oscillation, or move," Hadfield says. "And depending on what else is going on in the ship, that could not only disturb some science that's going on, but it could also be hazardous to the entire ship."

If the astronauts aren't mindful of what's going on elsewhere on the station, the movement caused by the treadmill could cause a crack, and then a leak.

But what happens when a fellow astronaut begins choking during a meal, or needs CPR or dental work?

"We are our own ambulance service, our own 911 and our own hospital and our own pharmacy," Hadfield says. "We have to be all of those things and take care of each other."

The ISS is outfitted with complete medical kits to deal with any health emergency, and every astronaut is prepared to do anything from administer CPR to pulling teeth.

For every mission, one crew member is trained as a "specialist," meaning he or she "knows everything about everything," says Hadfield, be it performing surgery or fixing the toilet. The level of expertise below that is "operator," meaning the crew member has a "practical working knowledge" of the procedures, while a "user" is an astronaut who can perform tasks at their most basic level.

If a doctor is among the astronauts, then he or she will get the brunt of the specialist medical training, Hadfield says. But the rest of the crew is trained to the highest level possible in case he or she is the one in need of help.

Medical emergencies in zero gravity pose a unique set of challenges. Performing CPR is nearly impossible if both the patient and the astronaut pumping his or her chest aren't strapped down. One technique, Hadfield says, is for the person performing the compressions to be suspended upside down over the patient, braced against the ceiling by the feet.

Blood floating around the ISS also poses a problem, and so sterilized cloths are used to swab a wound before any of it gets airborne.

And while lint and dust fall to the ground on Earth, not so in space.

"It's pretty easy and simple, but also pretty devastating, to get something in your eye when you're weightless," Hadfield says. "Every little bit of dust, every little metal shaving...it's a hazard to breathe, because you'll ingest them, and it's a hazard to get in your eye."

Warn, gather, work

Hadfield says that during a stay on the ISS, every astronaut is always on alert for a potential emergency, and is ready to sound an alarm if something is amiss.

Their system is first to warn everyone on board, gather everyone together to make sure everyone is safe, and then to begin "working the problem."

After the astronauts ensure that taking a breath is safe, they begin to look for the source of the problem. In the case of a leak, they constantly monitor the station's rate of depressurization to figure out how long they have before they are forced to abandon ship.

If they can't plug the leak in time, the astronauts climb into their vehicle, close the hatch and leave the ISS behind.

But dealing with such emergencies requires the astronauts to make it safely into space. During launch, any number of potential malfunctions could scuttle the mission. In the case of the Soyuz, a huge rocket is propelling the astronauts into space at 8 kilometres per second.

Anything less and the Soyuz can't make the trip, meaning the astronauts end up making an emergency landing "somewhere unplanned," Hadfield says. The Soyuz travels over Kazakhstan, the Himalayas, Mongolia and the Sea of Japan in the first 10 minutes of its trip, meaning the astronauts must also complete rigorous survival training on the chance it takes days for rescue crews to reach them.

But if all goes well and the astronauts get to fly home at the end of a mission as planned, they have to be prepared for everything from smoke in the capsule from an electrical short to a loss of pressure from a leak. The astronauts then "live inside the little cloth balloon" that is their pressure suit until they make it safely back to earth.

If the computers on the Soyuz fail and can't get the vessel back home, the astronauts have to fly the capsule themselves.

"You have to bring the airplane home completely manually, and we can point it, we can fire the engine just using a stopwatch and we can manually fly it through the atmosphere," Hadfield says. "We can fly our Soyuz back through the atmosphere like a steerable meteorite and land pretty accurately."

The years of training are necessary for the astronauts to keep themselves safe amid the myriad emergencies they can experience during a mission.

But as Hadfield points out, the astronauts aren't travelling to space just to risk their lives or have a little fun or do something cool. They travel to the ISS to conduct as many as 100 experiments at a time -- experiments that cannot be done on Earth.

"And that's why we're in space, because it's this wonderful international laboratory," Hadfield says. "But to safely do it, we just have to -- otherwise it would be irresponsible -- we have to gain all of these other skills. And that's why the training has to be so long and so in depth, otherwise we'd be unprepared for the things that are just bound to happen."