A pair of spacewalking astronauts were exposed to toxic ammonia while performing maintenance on the exterior of the International Space Station, requiring the crew to take extraordinary precautions to ensure the chemical didn’t contaminate the interior of the craft, the Associated Press reports.

During a seven-hour job performing replacement and checks on exterior systems, Victor Glover and Mike Hopkins replaced a hose that contained ammonia, used in the station’s cooling system.  As they uncoupled one end of the hose, ammonia crystals discharged and possibly hitting the astronauts.

“Oh yeah, look at that go. Did you see that?” Hopkins asked flight controllers as the ammonia, which immediate froze in the vacuum of space, dispersed. “There’s more than I thought.”

Flight controllers on the ground ordered the pair to decontaminate their suits prior to entering the station because they did not want the ammonia in the living and working areas of the ISS out of concern that even small amounts could sicken the crew or ruin on-board experiments.

The astronauts completed their other tasks–replacing an antenna for helmet cameras, rerouting ethernet cables, tightening connections on a European experiment platform, and installing a metal ring on the hatch thermal cover–before reentering the capsule, where they scrubbed down their suits.

The crew reported no smell or evidence of ammonia after the incident.