"Any Haz-Mat in the united states Must By law be clearly marked. At least at a commercial level.

Most of the containers that store them are built to be very very durable, so as long as they aren't sitting in water most materials should be ok for a long time."

"For oxyfuel welding you want to find acetylene cylinders.

for oxyfuel cutting you can use a multitude of gases.

Acetylene
Propane
Propylene (propene)
Mapp
Natural Gas
Butane

For OxyFuel cutting i'd choose Propylene or propane over the more popular acetylene. Both Gases have a much higher BTU/Ft3 and are therefor more effective in cutting. An additional perk is both gases are stored as a liquid meaning that there is more gas per tank. Acetylene is very unstable and must be stabilized in acetone to prevent it from exploding past 15psi. Its worth noting that if you plan on using gases other than acetylene for cutting you need tips that have additional preheat holes (generally 7 instead of like 12 or 14)

Avoid Cryogenic tanks. These can be identified by being fatter than normal tanks and they have a series of pipes and valves on the top. The reason i say to avoid these tanks is that they are constantly bleeding off gas as they heat, so after a week or two they are toast.

All the tanks will be clearly labeled with their contents. Any Gas cylinder should be transported with a safety cap and should be held securely in the upright position."