Scuba Diving Theories for Dummies – Part 5: Dive Tables Made Easy

Welcome back to our “Scuba Diving Theories for Dummies” series! In this installment, we’re diving into the world of dive tables. These tables might look intimidating at first glance, but don’t worry. We’re here to make them as easy to understand as your ABCs. Whether you’re a newbie diver or just brushing up on your skills, mastering dive tables is essential for safe and enjoyable dives.

What Are Dive Tables?

Dive tables are essential tools for scuba divers to plan their dives safely. They help you avoid decompression sickness by allowing you to monitor and control your nitrogen levels. The tables ensure you stay within no-decompression limits, which means you won’t need to make mandatory decompression stops on your way to the surface.

Breaking Down the Dive Tables

Let’s break down the tables, focusing on their main components and how to use them effectively.

Table 1: No-Decompression Limits and Repetitive Group Designation

Purpose: This table helps you determine how long you can safely stay at a certain depth without needing a decompression stop.

How to Use It:

  1. Find Your Depth: Look for the depth of your dive in meters on the far left column.
  2. Find Your Time: Move horizontally across the row to find the maximum time you can spend at that depth (in minutes).
  3. Group Designation: At the bottom of the column, you’ll see a letter (Group Designation). This letter represents the amount of nitrogen absorbed during your dive.

Example: If you plan to dive to 18 meters, the table might show you can stay for up to 50 minutes, resulting in a Group Designation of “G”.

Table 2: Residual Nitrogen Timetable for Repetitive Dives

Purpose: This table is used to calculate your nitrogen levels during surface intervals and to determine your new Group Designation before a repetitive dive.

How to Use It:

  1. Enter with Your Group Designation: Start with the letter from Table 1 (or previous dive).
  2. Follow the Arrow Down: Find the corresponding letter on the same column in Table 2.
  3. Surface Interval: Read to the left to find the time range of your surface interval (e.g., 1:00-1:30 hours).
  4. New Group Designation: Read down to the new letter. This is your starting Group Designation for your next dive.

Example: After a dive with a Group Designation of “G”, if your surface interval is 2 hours, you might move down to Group “D”.

Table 3: Adjusted No-Decompression Time Limits for Repetitive Dives

Purpose: To calculate how long you can stay underwater on your next dive without decompression stops.

How to Use It:

  1. New Group Designation: Use the new letter from Table 2.
  2. Planned Depth: Find the depth for your next dive on the left column.
  3. Residual Nitrogen Time and Adjusted No-Decompression Limit: The box where your depth row and Group Designation column intersect contains two numbers. The top number is the residual nitrogen time, and the bottom number is your maximum adjusted no-decompression time.

Example: With a Group “D” and planning to dive to 15 meters, the table might show 29 minutes of residual nitrogen time and an adjusted no-decompression limit of 41 minutes.

Tips for Using Dive Tables

  1. Plan Ahead: Always plan your dives and surface intervals using the tables to avoid decompression sickness.
  2. Safety Stops: Even if not required, make a safety stop at 5 meters for 3-5 minutes to further reduce nitrogen levels.
  3. Use Dive Computers: While tables are great, dive computers can provide real-time calculations and adjustments.


Understanding dive tables is crucial for safe diving. They help manage your nitrogen levels and plan your dives to avoid decompression sickness. By following the steps outlined in this guide, you can confidently use dive tables and enjoy your underwater adventures safely.

Remember, practice makes perfect, and the more you use the tables, the easier they become. Stay safe, dive smart, and happy bubbles!

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