Cave diver training stages and terminology

Reading about cave diving is no substitute for supervised training. This article explains the stages most agencies use and the words divers meet along the way. The definitions are conceptual: none of this is a dive plan or a procedure.

The common shape of a training path

Most agencies divide cave training into three broad steps, though names and boundaries vary.

• Cavern. Training in the daylight zone near the entrance (see Cavern and cave diving: what is the difference).
• Introductory or limited cave. The first dives beyond daylight, normally along one main line with few or no navigation decisions. TDI calls this Intro to Cave Diver and allows graduates to make single-guideline cave dives without direct supervision within the rule of thirds and 40 m ^[1]. GUE's Cave 1 permits limited penetration with a stricter gas allowance, no required decompression stops and no complex navigation ^[2]. SSI's Cave Diving teaches penetration with a single navigational choice ^[3]. The NSS-CDS Apprentice Cave Diver is Part I of its full certification and concentrates on limited penetration along the main line and on emergency skills ^[4].
• Full cave. Adds navigation through junctions, a larger share of gas and, often, decompression. Examples include TDI Full Cave Diver, GUE Cave 2, NSS-CDS Cave Diver, SSI Full Cave Diving and CDAA Cave Diver ^{[5][6][7][8][9]}.

Beyond full cave, agencies offer specialities such as stage cylinders, scooters, rebreathers, sidemount in tight passages and survey (see Specialist areas: sidemount, rebreathers, scooters, surveying and scientific diving).

Ladders change over time. The NSS-CDS replaced a four-level modular programme around 2019-2020 with a non-certification orientation, Apprentice Cave and Cave, partly so that students spend more training time in the equipment configuration they intend to dive ^[10]. UTD issues its restricted Cave 1 card only when a student cannot complete the full Cave 2 class, and lets Cave 1 expire after 24 months ^[11]. Course names that look alike can mean different things, and this reference does not assume two agencies' courses are equivalent unless an agency says so.

Some systems are organised differently altogether. The FFESSM grades divers by the zones they may dive in and by whom they must dive with ^[12]; the CDAA ties its levels to rated site categories ^[13]; and the British Cave Diving Group qualifies divers through volunteer mentoring and a vote of a section's qualified divers rather than a fixed-length course ^[14].

Glossary

Guideline. A line laid or followed from open water into the cave so the team always has a continuous physical route back to the surface. Exley's accident analysis named the failure to use a single, continuous guideline from the entrance as a leading cause of the deaths he studied ^[15].

Permanent line, main line. Line left installed in a cave, usually along the principal passage. Divers do not rely on it to reach open water: GUE Cave 1 students, for example, must show they can run a reel from open water until the team ties into the main line ^[2].

Primary reel and safety spool. The primary reel holds the line used to connect open water to the permanent line. A safety spool is a smaller line each diver carries for emergencies. Agency equipment lists specify both ^[2][4].

Jump. Moving from one line to another, for example from a main line into a side passage, by placing a short connecting line between them. GUE calls the device a jump spool and introduces it at Cave 2 ^[6]; TDI's full cave course includes using reels for jumps and gaps ^[5].

Gap. A break where one line ends and another begins a short distance away. GUE notes that this normally happens where a line has reached another entrance, and allows Cave 1 trainees to navigate gaps while keeping jumps for Cave 2 ^[2].

Intersection (T or Y). A point where lines meet. GUE distinguishes permanent intersections from temporary ones created by a diver's own jump spool, and allows Cave 1 divers past only one permanent intersection ^[2].

Circuit and traverse. A circuit is a route that loops back to a known point; a traverse enters by one entrance and leaves by another. NSS-CDS full cave training covers at least the theory of both, including the idea of a halfway point or point of no return ^[7].

Line markers. Directional markers point toward an exit; non-directional markers mark a position without indicating direction. Agencies require divers to carry both kinds ^[2][4].

Restriction. A narrow part of a cave. Exley described it simply as a tight or narrow area ^[15]. The AAUS scientific diving manual gives a practical definition: any passage through which two divers cannot easily pass side by side while sharing air ^[16]. TDI's cavern limits exclude areas too small for two divers to swim side by side ^[17].

Siphon and sump. These words are used differently in different places. In the AAUS manual, a siphoning cave is one where flow is directed into the cave, which can draw in mud and silt and reduce visibility ^[16]. In French cave diving, siphon means a flooded section of cave passage, and the FFESSM counts dives in multi-sump caves toward its highest level ^[18]. British cave divers use sump for a flooded passage, and the Cave Diving Group's training records include sump travel ^[14].

Halocline. A layer where salinity changes sharply with depth. In water-filled limestone caves near the sea, lighter fresh water can lie over salt water; the boundary blurs vision and has been described as giving an illusion of an air space ^[19].

Silt-out. Loss of visibility when fine sediment is stirred up. Exley included avoiding silt among his ten recommendations ^[15], and agency courses such as GUE Cave 1 and TDI Cavern Diver train propulsion and anti-silting techniques ^[2][17].

Rule of thirds. A gas-planning convention in which no more than about a third of the starting supply is used going in, so that the rest remains for the exit and for helping a teammate. Exley found that failing to keep at least two-thirds for the exit and emergencies ranked close behind the lack of a guideline as a cause of fatalities ^[15]. Agencies apply variations: TDI uses one-sixth for cavern and intro divers on doubles and SSI teaches the rule of sixths at cavern level ^[17][20]; GUE limits Cave 1 to one-third of two-thirds of total gas ^[2]; the FFESSM's PS1 and PS2 documents refer to a rule of quarters ^[12]. These are conventions taught and checked under supervision, not formulas to adopt from a reference page.

Dissimilar volumes and gas matching. When teammates carry different amounts of gas, plans have to account for it so that each diver could get the other out. TDI and CMAS courses cover gas management for dissimilar volumes ^[17][21].

Stage cylinder. An extra cylinder carried for part of a dive, typically placed and collected along the way. GUE introduces stages at Cave 2 ^[6], and the CDAA describes its Advanced Cave sites as requiring stage diving ^[22].

Light zone or daylight zone. The area near an entrance where natural light is visible. Most cavern limits are defined around it ^[20][23].

S-drill. A pre-dive check of teammates' equipment, especially gas delivery. The AAUS manual requires one on every scientific cave dive ^[16], and CDAA Basic Cave skill sessions include S drills ^[24].

Why the terms matter

Agencies express their limits in this vocabulary: no jumps, one permanent intersection, no restrictions, a fraction of the gas supply. Knowing the words helps a diver read a course standard and understand exactly what the card in their pocket does and does not cover. What the words cannot do is teach the skills behind them; that requires an instructor, in the water.