There is no standardized definition to catagorise either dive sites or divers.
Dive site descriptions/ratings are mostly dictated by individual dive operators. Neither is there a standardized industry-wide definition on what rating/experience a diver must have to be considered beginner/advanced etc.
Here are a list of factors that can be used to catagorise dive sites:
1. Dive Depth. Many dive centers predominantly use dive depth to reflect the 'level' of the dive. This is often linked to the most common depth qualifications issued by the major certifying agencies (i.e. 18m- beginner / 18-30m intermediate / 30m+ advanced). There are two major considerations when matching depth against experience/training;
a. Narcosis. Recognising and reacting effectively to narcosis can be very dependant on experience.
b. Gas and (No-)Deco awareness. Greater depth has a proportional impact on reducing the time provided by gas supplies and no-decompression limits. The deeper you are, the less flexibility and contingency exists to cope with distractions, incidents, delays etc.
2. Bottom Depth. Many dive centers will automatically catagorize a dive as 'advanced' if the bottom is below recreational diving limits (deep wall dive). Loss of descent control could prove dangerous/fatal. Likewise, a dive where the bottom depth exceeds the planned dive depth (wall dive) may be counted as intermediate, because bouyancy control is required. Where dive depths coincide with bottom depths (dives conducted along bottom contours) then loss of bouyancy control is less dangerous.
3. Current. Strong currents, tides and swells can cause an increase in the catagorisation of a dive site. This is especially true if they require specific or advanced techniques that may not always be taught at beginner/entry level (i.e. drift diving, use of reef hooks, DSMBs etc)
4. Visibility. This can be very dependant on location. A bad-viz (more advanced) dive in the tropics could be classified as a good-viz (beginner) dive in temperate waters. Generally, when one dive site experiences considerably worse visibility than other sites in the local vacinity, or compared to the regional norm, then it can be classified as more advanced. Liekwise changes of visibility during a day/week/year can mean the classification of a dive site changes (including night diving).
5. Specific Hazards. There could be specific hazards applicable to individual sites that would raise the complexity of the dives or present a requirement for greater experience and/or training to ensure diver safety. In essense, the dive operator would want those divers to have sufficient experience and training to be able to conduct the necessary risk assessments and hazard awareness throughout the conduct of the dive. These hazards could include, but not limited to, issues such as:
a. Overhead environments.
b. Aggressive or dangerous marine life.
c. Confusing topography/bottom.
d. Entanglement hazard (wrecks, weed etc)
e. Wrecks that risk collapse etc
f. Sites with rapid current/tidal direction changes.
6. Sites Requiring Specific Diving Experience or Training. With knowledge of the core training provided by the major certifying agencies, dive centers can differentiate sites based on reasonable assumptions/expectations of the training and/or experience likely to be present in divers of different qualification levels. This could include wreck diving, cave diving, drift diving etc etc. It could also include consideration of how much support is available to divers at the site;
a. Ascent/descent line - or free ascent/descent.
b. Type of supervision (Divemaster, in-water guide, out-of water supervision or nothing?)
c. Restricted geographic area (small lake, bay etc).
7. Sites with 'Temptations'. Some sites have features that may tempt less experienced divers to exceed the limitations of their training and/or experience. Where those temptations may pose significant danger, the whole site may recieve a higher grading. Examples will be: deceptively dangerous opportunities to penetrate wrecks, easily accessible cavern/cave penetrations, highly attractive marine life below maximum dive depths etc etc. In essense, sites where morons will be drawn towards the inevitability of Darwin's Law...
8. Sites of specific environmental fragility. Inexperienced divers are sometimes limited from certain sites due to measures in place to reduce diver impact and damage on fragile sites. For instance, dive operators may wish to ensure that only divers with exceptional bouyancy control visit sites with fragile, rare or recovering coral systems.
9. Temperature. Whilst temperature can be offset by the correct exposure protection, colder water does pose greater risks. Dive operations may want to ensure that divers have sufficient experience and training to understand and monitor those risks.
