"In spite of the dangers of hydrogen, NASA lacked a comprehensive system for detecting a leak for much of its career. Part of hydrogen's danger is that it gives off low radiant heat, meaning its flame is invisible in daylight. NASA came up with a rather creative solution for the issue.
"During the Apollo missions, scientists and engineers would simply walk through the facilities with a long broom held out in front of them. When the broom touched the invisible burning hydrogen, the end would suddenly combust and they could mark another area which had dangerous gas within it."
Quoting:
"In spite of the dangers of hydrogen, NASA lacked a comprehensive system for detecting a leak for much of its career. Part of hydrogen's danger is that it gives off low radiant heat, meaning its flame is invisible in daylight. NASA came up with a rather creative solution for the issue.
"During the Apollo missions, scientists and engineers would simply walk through the facilities with a long broom held out in front of them. When the broom touched the invisible burning hydrogen, the end would suddenly combust and they could mark another area which had dangerous gas within it."