We do use them.
It's not the best, nor most modern system, and I personally would love to see something better, but I know it would take a significant amount of engineering to install.
The beauty of the Chemox system is that a small box of chemical cannisters holds enough air for 6 hours.
6 hours worth of air bottles is a half dozen large air flasks. Which need special handling/storage because they're pressurized.
Having a smaller number of bottles is do-able, but only if you have refill stations and lines through the ship, which means a whole new HP Air system installed, capable of providing BREATHABLE SAFE air to users.
Then there's the re-training. Currently, there's only the CSE Departments and the firefighters that are trained in Scott Air Packs, and the time needed to retrain the entire fleet? YIKES.
Anyhow.
They're not great, and not all of us like them. When I have personally seen them in 3 seperate museums, I get worried...
But, they're what we have, and they've worked in the fires that we have had on ships in the past number of years. Ideal no, but they work and we get by. Welcome to the Navy.
NS