Gradient Factor(GF)

A diver goes to 50m/165ft for 20 minutes bottom time, using Trimix 18/45 (18% oxygen, 45% helium) as back gas, and oxygen for decompression from 6m (20ft) on. Descent rate is 15m/min (50ft/min) and ascent rate is 10m/min (33ft/min). Decompression algorithm is based on Bühlmann ZH-L16B and the different decompression tables, based on five different GFs, are shown in Table 1.

These GF parameters are commonly used for different types of dives (e.g. rebreather, deep/cold dives, default values in some decompression SW) and GF 100/100 is shown here as a reference, since it is pure Bühlmann table (containing no margin, so it is also not very safe!). As clearly shown in Table 1, low GF Low numbers generate deeper stops. In fact, some divers use GF Low value of 10% to generate “deep stops”. Deep stops, also called “Pyle stops”, are a means to reduce micro bubbles during deeper phase of ascent. However, during deep stops, many slower tissues are still on-gassing and thus total decompression time will increase (but again, safety is worth for some added hangtime!). Small GF High values generate longer shallow stops, as also seen in Table 1.

출처 : http://evolution.com.ph/wp-content/uploads/divedocs/Gradient_Factors.pdf