Snow cleaning of the world's largest telescope mirrors was an impressive sight. The optics technicians would climb into a huge telescopic boom lift and spray immense clouds of cold carbon dioxide snow and gas onto the ten meter diameter mirrors high above the floor indoors. It would cause some of the accumulated dirt to magically fall off, leaving it less dirty.
I made the mistake of using my earned sick time at the W. M. Keck Observatory for essential surgery. When I returned to work the management team demanded my resignation numerous times, citing my essential surgery as a reason. The W. M. Keck Observatory taught me that using earned sick time in the USA may put your future employment at significant risk.
I saw a guy faint at the W. M. Keck Observatory, he stepped out from the tour group and said to me "I'm feeling sick" and then his eyes rolled back and his knees gave way! The group caught him on his way to the ground and he got free emergency medical oxygen for half an hour before being evacuated off the summit by his tour group!!! His friends stated that he was considered the healthiest person in the group while he was gasping for breaths of life on the summit of Mauna Kea! Never saw him again.
When I was instructed to use medical oxygen to do my job at the W. M. Keck Observatory from 2001 to 2006, I was never told about the legal health information that is now posted on oxygen cylinders. My memories of the green medical oxygen cylinders that we would use daily is that they had no information on them and we were never given a recognised legal oxygen administration training course for routine daily use or a medical prescription from a doctor. We were shown the three oxygen cylinders at the facility and told to use them whenever we developed headaches, which was multiple times daily. It was common to find all three oxygen cylinders in use by other very high altitude workers and to have to line up to get a turn on the magical medical gas.
When I worked at the W. M. Keck Observatory on the 13,796 feet very high altitude summit of Mauna Kea, we would routinely be engulfed in cold clouds of helium and nitrogen gas as we discharged it into the video camera systems daily. The management team never warned us that we were in a hazardous oxygen deprived environment during this activity that was known for its ability to adversely affect physical and mental health, and possibly bring on death by asphyxiation.