SAC — Surface Air Consumption

Surface Air Consumption (SAC) is your breathing rate measured at the surface. It tells you how many liters of air you use every minute.

How SAC works in practice

Your SAC rate measures gas volume. A relaxed diver usually uses 15 to 20 liters per minute. This number stays constant even when you change depths.

You must adjust for ambient pressure. While you dive at 30 m, the pressure is 4 ata. This means you consume 4 times more air than at the surface. I remember calculating this in Labuan Bajo during a 2018 trip.

Math determines your gas supply. You divide your air consumption by the current pressure because density increases with depth. It is a vital tool for every diver.

Why it matters for safety

Planning prevents emergencies. Divers use this number to calculate how much gas remains in a tank. I used my SAC rate to plan long deco stops in Komodo back in 2018.

Safety requires constant monitoring. High currents often spike this number. You should monitor your pressure gauge every 5 minutes so that you avoid running low on gas.

Stress changes everything. If your rate jumps to 30 liters, you are likely working too hard or panicking. This sudden increase can lead to a dangerous situation.

Common calculation mistakes

Don’t use one dive. Do not rely on a single dive for an accurate calculation because stress changes your breathing. One bad dive in heavy surge will ruin your data.

Depth affects the math. Always check your depth before calculating your remaining air time. A mistake here leads to wrong reserve calculations.

Data must be averaged. You should record your pressure at the start and end of a 45 minute dive. This provides a more realistic average for your logbook.

SAC and related concepts

SAC connects to RMV. Respiratory Minute Volume is the actual amount of gas you breathe underwater. It is different from SAC because it includes depth pressure.

Gas management depends on this. If you know your SAC, you can predict your Surface Air Consumption Rate (SACR) for specific depths. This helps when planning deep dives in Anilao.

Plan your ascent carefully. Knowing your rate allows you to manage your remaining 50 bar reserve effectively. It keeps your dive profile within safe limits.

Check your pressure gauge every few minutes.