Scuba & Nitrox Glossary: C
Nitrox and breathing-gas terminology is prioritized first. General scuba terms follow below. Definitions are educational summaries and do not replace formal training, manufacturer instructions, or an operational dive plan.
Nitrox & Gas Terms — C
- CGA Grade E
- A compressed-air quality specification often referenced for breathing air; additional requirements may apply when air is used for oxygen-compatible blending.
- CNS Clock
- A dive-computer or planning display estimating central nervous system oxygen exposure as a percentage of an adopted limit.
- CNS Oxygen Toxicity
- Potential acute effects of elevated oxygen partial pressure on the central nervous system; a convulsion underwater can be fatal.
- Continuous Blending
- Producing Nitrox by adding oxygen to an air stream before compression.
- Cylinder Contents Label
- A label identifying measured oxygen percentage and often analysis date, MOD, pressure, and analyzer or diver information.
- Cylinder Analysis
- Measuring the gas before diving and confirming that the result matches the dive plan.
- Calibration Adapter
- A fitting that presents calibration gas to an analyzer at controlled flow.
- Calibration Interval
- The planned frequency for checking and resetting analyzer response.
- Continuous-Blending Nitrox
- Nitrox made by adding oxygen to intake gas before compression using approved equipment.
- Crossover Fill
- Transferring gas between cylinders to redistribute pressure or mixture.
- Cylinder Contents Tag
- A tag recording analyzed mix, MOD, pressure, date, and analyzer initials.
General Scuba Terms — C
- C-Card
- Informal term for a diver certification card.
- Cave Diving
- Specialized overhead-environment diving requiring dedicated training and equipment.
- Closed-Circuit Rebreather (CCR)
- A system that recirculates breathing gas, removes carbon dioxide, and controls oxygen.
- Compass Navigation
- Using a magnetic compass and natural references to maintain direction underwater.
- Confined Water
- A pool or pool-like environment suitable for controlled training.
- Controlled Emergency Swimming Ascent (CESA)
- A trained emergency ascent while exhaling continuously; procedures vary by agency.
- Current
- Horizontal or vertical movement of water that affects navigation, workload, and gas use.
- Capillary Depth Gauge
- A simple gauge that estimates depth from compression of trapped air.
- Cavern Zone
- The naturally lit portion of an overhead environment with direct access to open water.
- Controlled Emergency Swimming Ascent
- A trained ascent technique used after loss of breathing gas in limited circumstances.
- Current Line
- A line deployed from a boat to help divers manage surface current.
- Cutting Device
- A knife, shears, or line cutter used to address entanglement.