A Beginner’s Guide to Understanding Dive Tables

When you first venture into the world of scuba diving, there is much to learn, from equipment handling to understanding dive physics. One essential tool for divers is the dive table. While modern dive computers have become increasingly popular, dive tables remain a fundamental part of diver safety and planning. These charts are used to calculate safe dive times and depths, preventing the risk of decompression sickness. In this guide, we will break down what dive tables are, how to read them, and why they are vital for divers at every level.

What are Dive Tables?

Dive tables are structured charts used by divers to plan dives and calculate no-decompression limits. These tables provide information on how long a diver can stay at a specific depth before needing to ascend to the surface in a safe and controlled manner. They account for the fact that as a diver descends, the pressure increases, causing nitrogen from the air to be absorbed into the body. If a diver stays at depth for too long and ascends too quickly, the nitrogen that has been absorbed into the tissues can form bubbles, causing decompression sickness. Dive tables help prevent this by indicating safe ascent rates and surface intervals.

The Structure of a Dive Table

A standard dive table typically contains several columns that correspond to different depths and times. The depth is measured in feet or meters, and the times represent the duration a diver can safely spend at that depth. As the depth increases, the allowable time at that depth decreases to avoid excessive nitrogen absorption.

The key components of a dive table include:

1. Depth: The depth at which you plan to dive, usually represented in feet or meters. As depth increases, the pressure on your body increases, which results in more nitrogen being absorbed into your tissues.
2. Time: The time you plan to spend at a given depth. The longer you stay at a specific depth, the more nitrogen your body will absorb.
3. No-Decompression Limits (NDL): The maximum time you can spend at a certain depth without needing to make a decompression stop on your ascent. Exceeding the NDL would require the diver to perform a decompression stop at a shallower depth to off-gas the accumulated nitrogen.
4. Safety Stop: Although not always mandatory, most divers are encouraged to make a safety stop at around 15 feet (5 meters) for a few minutes to allow their bodies to release any excess nitrogen before ascending to the surface.

How to Use a Dive Table

Using a dive table involves checking the depth and time of your planned dive and then referencing the table to determine whether you will be within safe limits. Here’s a step-by-step breakdown of how to use a dive table:

1. Select your planned depth: Determine the maximum depth you plan to reach during the dive. This is typically the deepest point of your dive.
2. Determine the time you plan to spend at that depth: Based on the type of dive you’re planning, decide how long you will stay at that depth. Remember, the deeper you go, the less time you can stay without exceeding the safe limits for nitrogen absorption.
3. Check the No-Decompression Limit: Using the depth and time, find the corresponding no-decompression limit on the table. If your planned time is equal to or less than the limit, you are within safe parameters. If it exceeds the NDL, you will need to adjust your dive plan or consider making a decompression stop.
4. Consider multiple dives: If you plan multiple dives in a day, you’ll need to adjust your dive time based on residual nitrogen. Most dive tables offer “repetitive dive” tables to help account for nitrogen that has been absorbed in prior dives.

Why Dive Tables Are Important

Dive tables play a critical role in ensuring diver safety. Without a dive table, it would be difficult to calculate how long one can safely stay at a certain depth. If nitrogen bubbles form in the tissues and bloodstream, they can lead to decompression sickness, which can be life-threatening.

While dive computers are now widely used for real-time calculations, dive tables remain a valuable skill to master, especially for new divers. They provide a reliable backup to a dive computer and offer a better understanding of how depth and time affect the body. Furthermore, dive tables encourage divers to think critically about dive planning, leading to safer diving practices.

Common Dive Table Mistakes to Avoid

1. Exceeding no-decompression limits: One of the most common mistakes divers make is staying at depth too long, exceeding the no-decompression limits. This can put them at risk of decompression sickness if they don’t stop at the proper depth for a decompression stop on their ascent.
2. Ignoring repetitive dive rules: When planning multiple dives in one day, it is essential to account for residual nitrogen from previous dives. If you fail to adjust your plans, you could exceed safe limits, leading to an increased risk of decompression sickness.
3. Improper ascent rate: Even if you have stayed within the recommended no-decompression limits, ascending too quickly can cause nitrogen bubbles to form, resulting in decompression sickness. Always adhere to the recommended ascent rate of no faster than 30 feet per minute (9 meters per minute).

Modern Dive Computers vs. Dive Tables

While dive tables have been a mainstay in the diving community for decades, many divers now rely on dive computers for real-time calculations. Dive computers continuously monitor depth and time, automatically adjusting no-decompression limits as the dive progresses. These devices take the guesswork out of dive planning, offering more convenience for the diver. However, it is still highly recommended that divers learn how to use dive tables, as they provide a strong foundation in understanding dive physics and nitrogen absorption.

Conclusion

Learning how to read and understand dive tables is an essential skill for every diver. These tables help ensure safe dive times, depths, and ascent procedures, reducing the risk of decompression sickness and ensuring a safe and enjoyable diving experience. Whether you’re using a dive computer or a traditional table, understanding the science behind it is key to becoming a skilled and responsible diver. By taking the time to learn dive tables and dive planning, you lay the groundwork for a lifetime of safe diving adventures.