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. Various dive agencies use different terms to describe the same idea: Surface Air Consumption (SAC), Respiratory Minute Volume (RMV), and Surface Consumption Rate (SCR). To reduce confusion, this page compares how RAID, NAUI, PADI, SSI, SDI/TDI, GUE, and NOAA define and apply these terms.
Important: Where possible, this comparison relies on publicly accessible sources. Many agencies restrict even basic terminology behind paywalls or instructor portals, which limits clarity for divers comparing programs. In contrast, NOAA deserve recognition for openly publishing their standards and terminology.
Surface Air Consumption (SAC)
Definition: The rate of gas a diver consumes per minute at the surface, typically in psi/min or bar/min (pressure based).
- PADI: Reported pressure based. No public documentation.
- SSI: Reported pressure based. No public documentation.
- NAUI: Reported pressure based. No public documentation.
- 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: Unique Approach
Both appear to invert the standard terms. SDI/TDI also rename RMV to Required Minute Volume.
- SAC: Volume at surface (L/min)
- RMV: Depth adjusted (SAC x ATA)
- Terminology used contrary to NOAA, PADI, SSI, NAUI, and GUE. [1], [3]
Surface Consumption Rate (SCR)
Used by GUE instead of SAC or RMV to avoid ambiguity. SCR equals a surface normalized gas rate in liters or cubic feet per minute.
- GUE: Uses SCR (and DCR), 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 ft^3/min | Avoids SAC and RMV entirely. [4] |
| NOAA | SAC, RMV | psi/min, ft^3/min | Clear distinction; publicly available definitions. [2] |
References
- Air Management: More Than an Occasional Glance at an SPG! - TDI
- NOAA Diving Standards and Safety Manual (2023) - Appendix 2
- RAID Instructor Explains SAC and RMV (YouTube - removed after publishing)
- GUE Instructor Explains SCR and DCR (YouTube)