The NAPI Safe Diving Principles:

Part 4: Drinking and Diving


Lets face it: divers drink. Fish become bigger, depths deeper, dives longer and sharks closer after a few drinks. The problem is that diving after a heavy night of story telling is frowned upon by most diving agencies. They have rules such as "12 hours flask to mask", and others. Yet surely these rules are over simplified and generalized? After all, one glass of wine and a crate of beer are two different things, yet in each case one has to wait 12 hours before diving! Surely there must be a more scientific approach to drinking and diving? NAPI decided to use the scientific approach and investigated.

The Breaking Down of Alcohol

Investigations have shown that alcohol and nitrogen behave similarly, in that both are removed over time from the tissues. As is well known, going diving increases nitrogen levels rapidly, yet it takes some time at the surface for the nitrogen to be eliminated. Similarly, alcohol levels are increased rapidly by drinking, and it also takes time for the alcohol levels to drop once one stops drinking. Alcohol has the advantage over nitrogen in that it is only broken down in one tissue; the liver. From careful observations NAPI established that this break-down occurs exponentially. If we take 12 hours as being the time needed to clear the body of alcohol (as implied in the "12 hours flask to mask" rule), and if it takes 6 time cycles for a tissue behaving exponentially to clear, it becomes obvious that alcohol has a half time of 2 hours.

Maximum Allowable Alcohol Levels

If most countries allow us to operate heavy machinery (that is, drive cars) with a maximum of 0.08% alcohol in the blood, then NAPI believes that 0.08% should be the limit for diving too. Thus, it is not necessary to clear the body completely of alcohol, but only enough to ensure that we do not exceed the legal level. With these facts it is now possible to create a table for Alcohol Breakdown.

The Alcohol Breakdown or Drinking Table

First, a few definitions: the tables use a common beer with 5% alcohol as its unit. This corresponds to a glass of wine, or a tot of spirits. We shall term this unit ALC, or Alcohol Loading Content. Drinking between 2 and 3 ALC's is equivalent to about 0.08% alcohol. For simplicity, we shall assume that the diver may safely drink up to 2 ALC's before reaching the legal limit, but if more is drunk one has to wait for the alcohol to break down, that is, wait until the equivalent of 2 ALC's remains. This waiting time, as well as the time between drinks, is called SIT, or Sobering-up Interval Time. After each SIT you still have a certain amount of RAV in you. RAV (spoken "rave", of course), or Residual ALC Value, is the remaining alcohol which has not been broken down yet.

Now let's look at the tables.

Table 1 shows the SIT to clear, that is, reach the legal limit, relative to your current ALC value. Always round ALC's up, for added safety. There is no SIT required up to 2 ALC's.

Table 2 shows the RAV left in you after a certain SIT, starting with a certain ALC level.

Remember to always go to the next higher level if on a boundary!

     Table 1: Time To Clear

   ALC Level
0->2	2->3	3->4	4->5	5->6	6->7	7->8	8->9	9->10
0:00	1:10	2:00	2:38	3:10	3:36	4:00	4:20	4:38
   SIT to Legally Clear in hours:minutes

     Table 2: RAV levels

ALC \	0-30m	30-60m	1-2hr	2-4hr	4-8hr	8-12hr	>12hr
1	0.8	0.7	0.5	0.3	0.1	0.0	0.0
2	1.7	1.4	1.0	0.5	0.1	0.0	0.0
3	2.5	2.1	1.5	0.8	0.2	0.0	0.0
4	3.4	2.8	2.0	1.0	0.3	0.1	0.0
5	4.2	3.5	2.5	1.3	0.3	0.1	0.0
6	5.0	4.2	3.0	1.5	0.4	0.1	0.0
7	5.9	5.0	3.5	1.8	0.4	0.1	0.0
8	6.7	5.7	4.0	2.0	0.5	0.1	0.0
9	7.6	6.4	4.5	2.3	0.6	0.1	0.0
10	8.4	7.1	5.0	2.5	0.6	0.2	0.0

How to use the Tables: a few examples

Example 1:

You drink 1 beer, 24 minutes later you drink a glass of wine, and 61 minutes later you drink a double whisky. What are your ALC and RAV values after each stage, and what, if any, is your mandatory SIT?

  • 1 beer = 1 ALC,
  • 1 glass of wine = 1 ALC,
  • double whiskey = 2 ALC's.

You drink the beer. What is your RAV after 24 minutes? In table 2, look up the ALC value (1) and the SIT value (column A). Your RAV is 0.8 ALC.

You drink the wine. Your new ALC is now 1 + 0.8 = 1.8 ALC. You SIT for 61 minutes. Round 1.8 ALC to 2, and 61 minutes puts you in column C, still in table 2. Your new RAV is 1.0 ALC.

You down your double whiskey, so your new ALC is 1.0 + 2.0 = 3.0 ALC's. Remember to round up to the higher value if on a boundary, so use 4 ALC's. Look up this value in table 1 and you will see that you need to SIT 2 hours exactly before you can dive again.

Example 2:

You decide to change your strategy and drink first the double whiskey, then the glass of wine, then the beer. Redo the calculations.

Drink whiskey = 2 ALC's, 24 minutes SIT -> RAV = 1.7 ALC's.

Drink wine = 1 ALC, new ALC is 1 + 1.7 = 2.7 ALC's. Use 3 ALC's, 61 minutes SIT -> RAV = 1.5 ALC's.

Drink beer = 1 ALC, new ALC is 1 + 1.5 = 2.5 ALC's. Looking up in table 1, rounding up to 3, this gives you 1 hour and 10 minutes of mandatory SIT before the next dive.

This example shows an important fact about drinking: drink your heaviest drinks first, and never reverse profile!

Acute Alcohol Sickness

As alcohol tolerance varies from person to person, it may be necessary to introduce fudge factors. If you are underweight, underfed, sick, tired or overdived, add 1/4 ALC to each drink for each of these factors. Failing to comply may lead to Acute Alcohol Sickness.

There are two manifestations of Acute Alcohol Sickness, type I and type II, which are unfortunately not mutually exclusive. Type I manifests itself as vomiting, type II is commonly known as the "hang over". If you suffer from either, it is recommended to have a 12 hour SIT before continuing diving. Remember that Saturation Drinking may also lead to Acute Alcohol Sickness, even with the introduction of fudge factors.

For more information on the history of Drinking Tables, and Acute Alcohol Sickness, read "Deeper into Drinking."


With the NAPI Drinking Tables you can now drink with confidence, and plan your drinking evening in detail. A quick glimpse at the tables will give you all the information about your current alcohol level, and how long you have to wait around before the next dive!

Remember: Plan your drink, drink your plan!

PS: Good News!

NAPI will shortly introduce the Drinking Computer! This simple device will show you your current ALC level, your remaining ALC level before you exceed the limit, and if you exceed the limit, your time to SIT. You just have to remember to tap the single button before each drink, pressing it as many times as there are ALC's in your drink. Be even safer, use the Drinking Computer!


As usual, if you believe any of this, please contact NAPI, we have a course just for you!

Seriously, this is the best rubbish I've written so far, yet it sounds so good, so believable! Again, the tables are not complete fiction, but actually calculated.

This page was last updated on : 06 Sep 2011