Scuba & Nitrox Glossary: J
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 — J
- J-Cylinder
- A large high-pressure storage cylinder sometimes used in gas banks and blending operations.
- Joule Heating
- Temperature increase that can occur during rapid gas compression, relevant to oxygen-handling and filling safety.
- J-Size Oxygen Cylinder
- A large storage cylinder commonly used in gas-supply systems.
- Joule-Thomson Effect
- Temperature change that can occur when compressed gas expands through a restriction.
- Junction Pressure Gauge
- A gauge monitoring pressure at a blending-system connection.
- Jetting During Fill
- Localized heating or particle movement caused by high-velocity gas flow.
- Job-Site Oxygen Protocol
- Written oxygen-handling rules used by a fill station or dive operation.
General Scuba Terms — J
- Jackstay
- A line laid on the bottom to guide a patterned search.
- Jettisonable Weight
- Ballast designed to be released in an emergency.
- Jon Line
- A short line or strap used to secure a diver to an anchor or downline in current.
- Jump Line
- A guideline used to connect a main cave line to another passage.
- Jellyfish Sting
- An injury caused by contact with stinging cells from jellyfish or related animals.
- Jetty Dive
- A dive conducted along a man-made rock or concrete coastal structure.
- Jib Line
- A vessel line that may create an entanglement concern around divers.
- Joint Awareness
- Monitoring comfort and symptoms in joints after diving as part of post-dive awareness.
- Journey Dive
- A dive planned to travel along a route rather than remain near one entry point.