In scuba diving, GF refers to Gradient Factors, which are used in decompression algorithms to allow divers to control how quickly and closely their tissue compartments approach Bühlmann M-values during ascent.
Understanding Gradient Factors
Gradient factors are a key component of modern decompression algorithms, particularly those based on the Bühlmann model. They provide a mechanism for divers to personalize their decompression profiles, influencing the conservatism of their ascent.
How Gradient Factors Work
- Bühlmann M-Values: Bühlmann M-values represent the maximum allowable supersaturation for each tissue compartment in the body at a given depth. Exceeding these values increases the risk of decompression sickness (DCS).
- Controlling Ascent: Gradient factors modify the allowable supersaturation limits (M-values) during ascent. By setting different gradient factors, divers can control how close their tissue compartments get to the theoretical limits defined by the Bühlmann model.
Gradient Factor Notation
Gradient factors are typically expressed as two numbers, such as GF Low/GF High (e.g., 30/70 or 45/95).
- GF Low (First Number): Represents the gradient factor at the first stop. A higher GF Low will result in a deeper first stop and a more conservative ascent.
- GF High (Second Number): Represents the gradient factor at the surface. It controls how close the diver gets to the theoretical M-value limit upon surfacing. A lower GF High results in a more conservative ascent.
Practical Implications
- Deeper Stops: Using gradient factors effectively means the diver will be doing deeper stops, allowing more time for off-gassing at shallower depths, increasing their safety margins.
- Personalization: Gradient factors allow divers to adjust their decompression profiles based on factors such as age, fitness, dive history, and environmental conditions.
Example
A diver using a GF of 30/70 would have a more conservative ascent than a diver using 20/90 because:
- The 30 GF Low results in a deeper first stop, allowing more off-gassing at a greater depth than the 20 GF Low.
- The 70 GF High restricts the diver's theoretical nitrogen loading at the surface more so than the 90 GF High, causing an overall reduction in risk.
Summary
Gradient factors enhance the flexibility and safety of decompression procedures in scuba diving, allowing for personalized and conservative ascents.
