SAC, RMV, and SCR: Comparing Gas Consumption Terminology Across Dive Agencies
Understanding your breathing gas consumption is vital to safe diving and effective dive planning. However, various dive agencies use different terms: primarily Surface Air Consumption (SAC), Respiratory Minute Volume (RMV), and Surface Consumption Rate (SCR) to describe this concept. Let's clarify the confusion by looking at how major agencies like RAID, NAUI, PADI, SSI, SDI/TDI, GUE, and NOAA define and apply these terms.
If you would like to know more about the basics of RMV, SAC and SCR; and why RMV and SCR are more valuable to know than SAC, I've got a deep dive on the topic.
Important: Where possible, this comparison is based on publicly accessible sources. Unfortunately, many major dive agencies restrict access to even basic terminology—like SAC and RMV—behind paywalls or instructor-only portals. This lack of transparency makes it unnecessarily difficult for divers to compare training programs and build shared understanding. Confusion within the industry persists on this topic specifically because most agencies refuse to be transparent about what they teach and why.
In contrast, NOAA deserve recognition for openly publishing their training standards and making their terminology available to all divers.
Surface Air Consumption (SAC)
Definition: The rate of gas a diver consumes per minute at the surface, typically in psi/min or bar/min (i.e., pressure-based).
- PADI: Presumed pressure-based. No public documentation.
- SSI: Presumed pressure-based. No public documentation.
- NAUI: Reported as pressure-based. Not verifiable.
- NOAA: Defined explicitly as pressure-based. [2]
Respiratory Minute Volume (RMV)
Definition: The actual volume of gas (liters or cubic feet) consumed per minute at the surface—normalized to 1 ATA.
- PADI: Introduced in TecRec. Not publicly documented.
- SSI: Reported in Extended Range. Not verifiable.
- NAUI: Used in technical training. No public source.
- NOAA: Defined clearly and preferred for dive planning. [2]
RAID and SDI/TDI’s Unique Approach
Both seem to invert the standard terms. With SDI/TDI going so far as to rename RMV to Required Minute Volume...argh!
- SAC: Volume at surface (L/min)
- RMV: Depth-adjusted (SAC × ATA)
- Terminology used contrary to NOAA, PADI, SSI, NAUI and GUE. [1],[3]
Surface Consumption Rate (SCR)
Used by GUE instead of SAC/RMV to avoid ambiguity. SCR = surface-normalized gas rate in liters or cubic feet per minute.
- GUE: Only uses SCR, defined at 1 ATA. [4]
Agency Comparison Table
| Agency | Primary Term | Units Used | Notes |
|---|---|---|---|
| PADI | Unverified | Unverified | Reportedly follows standard distinction. Not publicly confirmed. |
| SSI | Unverified | Unverified | Reportedly follows standard distinction. Not publicly confirmed. |
| NAUI | Unverified | Unverified | Reportedly follows standard distinction. Not publicly confirmed. |
| SDI/TDI | SAC, RMV | L/min | Inverted use of RMV vs. other agencies. [1] |
| RAID | SAC, RMV | L/min | Inverted use of RMV vs. other agencies. [3] |
| GUE | SCR, DCR | L/min or ft³/min | Avoids SAC/RMV entirely. [4] |
| NOAA | SAC, RMV | psi/min, ft³/min | Clear distinction; fully open to public. [2] |
References
- Air Management: More Than an Occasional Glance at an SPG! – TDI
- NOAA Diving Standards & Safety Manual (2023) - Appendix 2
- RAID Instructor Explains SAC and RMV (YouTube - removed after publishing)
- GUE Instructor Explains SCR and DCR (YouTube)