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.
In high altitude astronomical facilities we routinely discharged large amounts of nitrogen gas into closed spaces. We were never informed by the astronomy management team about the abnormally low oxygen environments that the use of liquid nitrogen creates, how long term exposure to it manifests itself in human health and the resulting abnormal mental behaviors.
When I worked in high altitude astronomy, the worst sickness that I experienced was not at the 13,796 feet very high altitude summit of Mauna Kea Observatory (MKO) in Hawaii, it was at Kitt Peak National Observatory (KPNO) in Arizona at the much lower altitude of 6,875 feet. Due to my very high altitude experiences, I knew that this strange sickness was not primarily caused by altitude sickness and was most likely Sick Building Syndrome (SBS). After reporting various behavioral problems in all of the staff to the management team, my contract was not renewed, I was unable to legally protect the health and safety of the workers that I was responsible for, troubleshooting of this environmental problem stopped and I left in a sickened state for my next position before I could find the root cause.
When the National Optical Astronomy Observatory (NOAO) found out that Occupational Safety and Health Administration (OSHA) were going to visit the site to assist in bringing it into legal compliance, they freaked out! They insisted that the visit had to be canceled and the result was that I eventually became so sick from the toxic workplace environment that I had no option but to leave.
I have been through the OSHA system twice and I can confirm that I did not have the right to a safe workplace or whistle-blower protection on either occasion.
Oxygen deprivation and supplemental oxygen are both bio-hazards for Mauna Kea workers