Q: Like 100-200 meters or more. Straight air vs mixture what effects would one experience with straight air only. Dive speed approx 50M/min Great answer. Ever dive the blue hole near Tel Aviv? Oops, I meant Belize
A: It will be like dying. Safe sport diving depth limit is 130 feet. Diving deeper than this on air is extremely dangerous as you are likely to suffer from nitrogen narcosis at depth (like being drunk) and may have an attack of the "bends" (decompression sickness) upon ascending or after you are back on the surface. At 130ft you will only have a few minutes of bottom time before you must start your ascent to prevent bends due to buildup of nitrogen in your tissue. Breathing Oxygen-enriched air (also called Nitrox) reduces nitrogen buildup but adds a set of issues with Oxygen toxicity, which is another killer if you violate depth/% O2 combined limits. "Dive speed" on descent is limited to how fast you can equalize the pressure on your inner ears (think of having to "pop" your ears while descending from a high mountain or landing in an airplane -only way worse). To many people this is somewhat painful and must be done frequently (every few feet), thus slowing the descent. "Dive speed" is a killer on ascent - will cause the bends. In the old days the limit on ascent speed was 60ft/min. Now the recommendations are even slower (as slow as 15ft/min) and depend on depth segments of the ascent. "Safety stops" at particular depths (usually at 20 feet for a minimum of 2 minutes) are also recommended, along with slow ascent, to give your tissues time to out-gas nitrogen. Diving beyond 130 feet is classified as "technical diving" and requires special and expensive equipment and training so you wont get dead. All that being said........If you get the proper training and steadily acquire experience, while increasing your training level, diving is a fascinating hobby. Underwater photography, wildlife watching, and spearfishing are the most popular dive activities. To answer what i think is the intent of the original question: Since your body is mostly water, you dont "feel" any pressure effects other than your ears. You feel it there because the airspace in your sinus cavities and behind the eardrum want to close due to external water pressure. On descent, you have to continually "pop" or equalize the pressure (e.g.: fill the cavities with air at the same pressure of the surrounding water) by exercising muscles in the jaw and head or squeezing your nose and blowing "out your ears" to avoid severe pain and damage. If my sinuses are fairly clogged, I have to stop every few feet and do the nose squeeze/ear blow thing and it makes a squeaking sound in my head like pulling a large rubber item out of your ear each time, accompanied by a mild (or sometimes not so mild) transient inner ear pain. If my sinuses are really clear (fairly rare), i can descend slowly and my ears will periodically clear with just a jaw movement, still making the weird sound but with no or little pain each time. On ascent (at least for most people), the ears generally equalize themselves and make a similar sound to the descent and/or a more continuous sound like champagne bubbling inside your head. The sensation of flying or floating in space is really cool in high visibility (clear) water as you can see your buddies and fish also "flying" and things on the bottom. The visual sensation in low visibility water can be described as claustrophobic as there is no reference - only opaque "green" everywhere.