Beyond 130 feet: always a deco dive?

[Tigerman]

I would suggest you all pull your old dive books out and understand WHY there are issues below the 130 foot range.

For starters, look at gas laws. Oxygen toxicity starts to become an issue, as well as narcosis. That is why tech divers use inert gasses in their mix.

You all should take a Nitrox course, which will go into partial pressures in more depth, and discuss the above items.

It is a bit frightening that people on here think their fancy computer is going to solve the problem for them, without understanding gas laws and impact on the body. These are the same type of people that will penetrate a wreck, just because they purchased a $30 reel spool.

An OW card is a beginning level card. I tell folks it's realistically good to about 60 feet. Any deeper than that, and you really should get more training (deep diving class, for starters). Gear issues come into play, too, the deeper you go.

Tread carefully, and don't think reading stuff online qualifies you to endanger you and your dive buddy.

Oxtox is no issue till youre over 56m below the surface (184ft). Oxtox REALLY is the LEAST of your concerns "going below 130". Theres a LOT of ocean between 130ft and 184ft.
Narcosis, air consumption and the fact that you cant do a direct ascend if something happens is MUCH more relevant issues IMO.

Also, if you ARE diving some other gas than air, you know to mitigate the oxtox issue to begin with - unless youre doing that as well without any training that is..

 

[Rhone Man]

I would suggest you all pull your old dive books out and understand WHY there are issues below the 130 foot range.

I think the "why" must be narcosis for the 130 ft limit. If it was O2 toxicity the limit would be 185 ft. If it was deco risk, it could be anywhere, but would probably be shallower. If it was maximum realistic CESA depth, it would probably be around 90 ft or so. So I am betting on narcosis as the definitive factor for choosing that limit.

 

[boulderjohn]

I think the "why" must be narcosis for the 130 ft limit. If it was O2 toxicity the limit would be 185 ft. If it was deco risk, it could be anywhere, but would probably be shallower. If it was maximum realistic CESA depth, it would probably be around 90 ft or so. So I am betting on narcosis as the definitive factor for choosing that limit.

The PADI Encyclopedia of Recreational Diving says clearly that the primary reason for the 130 foot limit is narcosis.

 

[Gilldiver]

As Captain said, 130 is from the 1950's when the Navy came up with the standards for Navy divers using steel 72's. O2 tox was not considered to be an exceptional issue till ppO2 reached 2.0 (280 feet) for an inspection non-working dive or 1.6 (220 feet) for a working dive, the tables show air dives all the way down to 300 feet for up to 180 minutes - the total accent time, not total dive time, is 1,165 minutes, better be in a hard hat and surface supplied.

The fact of the matter is going over into deco at 130 is much less of a danger than doing the same at 60-80 feet, which is the most common bends depths.

From the Old US Navy Tables

depth NDL (Minutes) Required deco at NDL +1minute Required deco at NDL +5minutes
60 60 2 min at 10 feet 2 min at 10 feet
70 50 8 min at 10 feet 8 min at 10 feet
80 40 10 min at 10 feet 10 min at 10 feet
90 30 7 min at 10 feet 7 min at 10 feet
100 25 3 minutes at 10 feet 15 minutes at 10 feet
110 20 3 minutes at 10 feet 7 minutes at 10 feet
120 15 2 minutes at 10 feet 6 minutes at 10 feet
130 10 1 minute at 10 feet 4 minutes at 10 feet

So brushing deco by 1 minute has the most effect on the divers deco time in the range of 70 to 110 with the most impact at a depth of only 70 and 80 feet and blowing your BT by 5 minutes impacts you the most at 70 to 120. Actual impact at 130 in both cases would be cleared using the now standard 30 foot per minute accent and the 3 minute safety stop.

Note for the stops at 100, 110, 120, and 130 the times are given in 5 minute intervals, shallower times are in 10 minute intervals. What this means is that by doing a 130 foot dive for 15 minutes you use the next table up or the table for 20 minutes.

 

[captain]

This is the table from the 1958 Navy diving manual. The dividing depths are 30, 60 and 130. 60 and 130 match up with current OW and AOW standards. You can use any reason you want but this was the original reason.

 

[Rhone Man]

These are always the best threads on SB - when the old buzzards (no offence) come out of the woodwork and share lots of stuff from the old days that newer divers aren't familiar with. Good thread guys.

 

[captain]

These are always the best threads on SB - when the old buzzards (no offence) come out of the woodwork and share lots of stuff from the old days that newer divers aren't familiar with. Good thread guys.

Just trying to keep it real. Over the years many things have been assumed as to why we have this or do that, etc. I am not advocating that you dive any particular way, just know the real reasons why things are the way they are.

 

[mstachowsky]

And I wonder what it meant that a dive was "very unsuitable". how does that differ from an "unsuitable" dive?

 

[Gilldiver]

A lot of new/younger divers think that this was all studied and tested out when it was really the accumulation of a lot of practical knowledge the was then codified by the Navy. In many cases it is because it always has been and because we found that it worked.

Just like this: Why are Rail Road rails and highway lanes spaced the way they are?:

The origins of the standard gauge considerably pre-date the Roman Empire, and may even pre-date the invention of the wheel. The width of prehistoric vehicles was determined by a number of interacting factors which gave rise to a fairly standard vehicle width of a little under 2 m (6.6 ft). These factors have changed little over the millennia, and are still reflected in today's motor vehicles. Road rutting was common in early roads, even with stone pavements. The initial impetus for the ruts probably came from the grooves made by sleds and slide cars dragged over the surfaces of ancient trackways. Since early carts had no steering and no brakes, negotiating hills and curves was dangerous, and cutting ruts into the stone helped them negotiate the hazardous parts of the roads.[4]
Neolithic wheeled carts found in Europe had gauges varying from 1.30 to 1.75 m (4 ft 3 in to 5 ft 9 in). By the Bronze age, wheel gauges appeared to have stabilized between 1.40 to 1.45 m (4 ft 7 in to 4 ft 9 in) which was attributed to a tradition in ancient technology which was perpetuated throughout European history.[5] The ancient Assyrians, Babylonians, Persians and Greeks constructed roads with artificial wheelruts cut in rock spaced the wheelspan of an ordinary carriage. Such ancient stone rutways connected major cities with sacred sites, such as Athens to Eleusis, Sparta to Ayklia, or Elis to Olympia. The gauge of these stone grooves was 1.38 to 1.44 m (4 ft 6 in to 4 ft 9 in). The largest number of preserved stone trackways, over 150, are found on Malta.[6]
The Roman Empire actually made less use of stone trackways than the prior Greek civilization because the Roman roads were much better than those of previous civilizations. However, there is evidence that the Romans used a more or less consistent wheel gauge adopted from the Greeks throughout Europe, and brought it to England with the Roman conquest of Britain in AD 43. After the Roman departure from Britain, this more-or-less standard gauge continued in use, so the wheel gauge of animal drawn vehicles in 19th century Britain was 1.4 to 1.5 m (4 ft 7 in to 4 ft 10 in). In 1814 George Stephenson copied the gauge of British coal wagons in his area (about 1.42 m or 4 ft 8 in) for his new locomotive, and for technical reasons widened it slightly to achieve the modern railway standard gauge of 1.435 m (4 ft 8+1⁄2 in).[4]

In other words, they are that wide because they always have been, there was no science or engineering involved. In the same way, some diving practices are used as we have always have done it that way and it works.

 

[DevonDiver]

.................... and for technical reasons widened it slightly to achieve the modern railway standard gauge of 1.435 m (4 ft 8+1⁄2 in).

Sounds like there was some science and technology behind those "technical reasons" you mentioned in the quote. Just saying......