>> reporter: three hours into the sfas wapace walk, the unit place. >> it's got to go in another inch or so. >> there you go. >> she's finished. pump module in position. >> reporter: the task is a delicate one. the equipment contains a noxious cooling fluid, ammonia. >> some of the dangers hooking up the big heavy ammonia lines, they're really thick and massive, and hooking those up of course, if you were to leak ammonia, it's not a very pleasant chemical. you couldn't bring it inside. so there's definitely risk there. >> reporter: the risk became reality when one of the fluid lines carrying that ammonia got tangled. the crew was able to free the line, but some frozen flakes of ammonia were released during the disconnection process, and it came in contact with the astronauts. >> we have seen very small flakes coming out. >> could you tell if any of the