Air Quality

Clean air is a must when mining underground for long periods of time so if you hang around lava pools digging for diamonds you are not likely going to last very long. Air quality doesn't become a hazard until the user is below Y=48, at that point things like torches, active furnaces, fires and lava pools will affect how fast your air drops. Air can be replenished underground by carrying plant material in your hotbar or placing them down close by as a sort of air refill station. If your air drops below 50% your screen will start becoming increasingly greener, at this point if you don't have a reliable source of clean air it's best to leave to the surface as fast as possible. At 25% mining fatigue and slowness kicks in and makes escape very difficult, and at 10% those effects will worsen and at this point if you are not near the surface escape becomes almost impossible.

Air reducing blocks:

• Active Furnace - 0.25%
• Torch - 0.25%/s
• Fire - 0.5%/s
• Lava - 1%/s

Air increasing blocks:

• Flower/Plant + 0.01%/s
• Leaves + 0.1%/s

Notable Things:

• Because the nether dimension is considered one big cave, your air there will always be dropping unless you are carrying plant material.
• Wearing a respirator will keep your oxygen level at 99-100% as long as the filters are still good. Respiration enchantment will act as a wearable clean air source. Respiration III basically nullifies most air loss.
• Air shafts directly to the surface will act as a significantly fast source of clean air in a pinch. Consider building one to a underground station you can stop by occasionally to top up.
• Carrying air source blocks in your hot bar still works in most cases. A stack of leaves is a good portable source of air.