In diving, TBT stands for Total Bottom Time.
Understanding Total Bottom Time (TBT)
Total Bottom Time (TBT) is a crucial concept in dive planning, particularly when calculating decompression requirements. It accounts for the accumulated nitrogen in a diver's body from previous dives, ensuring safe ascent and minimizing the risk of decompression sickness.
How TBT is Calculated
According to the provided reference, TBT is calculated by adding two key values:
- Actual Bottom Time (ABT): The planned duration of the dive at the maximum depth.
- Residual Nitrogen Time (RNT): This represents the amount of nitrogen theoretically remaining in the diver's body from any previous dives.
The formula is:
TBT = ABT + RNT
Why TBT Matters
TBT, also referred to as Total Nitrogen Time (TNT), is a vital parameter for determining the appropriate decompression schedule for a planned dive. Divers use their TBT to consult dive tables or dive computers, which then provide information on:
- Decompression stops: How long and at what depths the diver needs to pause during ascent to safely release accumulated nitrogen.
- Ascent rate: The recommended speed at which the diver should ascend to the surface.
Example
Let's say a diver plans a dive with an ABT of 30 minutes. After reviewing their dive history, they determine their RNT to be 15 minutes. Therefore:
TBT = 30 minutes (ABT) + 15 minutes (RNT) = 45 minutes
The diver would then use 45 minutes as their bottom time when consulting dive tables or their dive computer.
