### Residual Nitrogen Time Explained:

### Tracking Nitrogen Absorption Over a Series of Dives Requires Simple Math:

### A Simplified Review of Nitrogen Absorption When Scuba Diving:

### Nitrogen Remains in a Diver's Body Long After He Surfaces:

### How Do We Measure Nitrogen in a Diver's Body?:

This is where dive theory gets pretty interesting. Left-over nitrogen (or *residual nitrogen*) in a diver's body is measured in units of time. Yes, that's right, we measure nitrogen in minutes. This might seem illogical at first, but remember that time is required for a diver's body to absorb nitrogen. For example, it takes five minutes to absorb "x" amount of nitrogen. In diving, we can refer to that "x" amount of nitrogen as "five minutes of nitrogen". Almost . . . .

Remember that two factors affect nitrogen absorption - time and depth. The deeper a diver descends, the more quickly he absorbs nitrogen. It might take him five minutes to absorb "x" amount of nitrogen at a shallow depth, and only two minutes to absorb "x" amount of nitrogen at a deeper depth. For this reason, when we refer to nitrogen in "minutes of nitrogen" we also have to state depth. If a diver's body absorbs "x" amount of nitrogen in five minutes at forty feet of depth, we can say he has "five minutes of nitrogen at forty feet." This is his residual nitrogen time.

### Residual Nitrogen Time Helps to Track Nitrogen Absorption Over a Series of Dives:

At the beginning of a second, third, or fourth dive of the day, a diver still has some residual nitrogen in his body from his previous dives. Residual nitrogen time accounts for this left-over nitrogen. A diver descends to a given depth, and even though he just began his dive, he has the same amount of nitrogen in his system as if he had already been diving at the depth for some number of minutes -- the residual nitrogen time.

We already know that on a single dive, divers track nitrogen absorption according to minutes at certain depth. A diver on a repetitive dive can no longer use his actual dive time and depth to calculate his nitrogen absorption because he already has some nitrogen in his body when he starts the dive. However, if we add his residual nitrogen time to his actual dive time, we come up with a time in minutes that is representative of the actual amount of nitrogen in his system.

For this reason, when determining a diver's nitrogen absorption after a repetitive dive, we add his residual nitrogen time and his actual dive time together, and use the resulting number of minutes and his maximum dive depth to calculate his nitrogen absorption. These two numbers can be used on dive tables without any further adjustments.

### How Does a Diver Calculate His Residual Nitrogen Time?:

• Run down the column/row listing the diver's pressure group after his surface interval until it intersects the row/column listing the maximum depth of his dive.

• The diver's residual nitrogen time is listed in this box.

• If two numbers are listed in this box, use the legend on the dive table to determine which number is the residual nitrogen time.

### The Take-Home Message About Residual Nitrogen Times:

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