The scene where Ethan Hunt dives to a depth of 500 meters and survives without protective equipment in Mission: Impossible - Dead Reckoning Part 2 is extremely far from reality—essentially impossible. Here’s why:

1. Pressure at Depth
• At 500 meters, the water pressure is approximately 50 atmospheres (50 times the pressure at the surface).
• Without a specialized suit or submarine, the human body would be crushed instantly due to the sheer force exerted by the water at this depth.

2. Human Dive Limits
• The deepest recorded free dive by a human is 214 meters (achieved by Herbert Nitsch in 2007), and he was equipped with rigorous training, specialized techniques, and safety equipment.
• Even with scuba gear, recreational divers rarely exceed 40 meters due to risks like nitrogen narcosis and oxygen toxicity. Specialized deep-sea divers may reach up to 300 meters using advanced technology like saturation diving.

3. Temperature
• At 500 meters, water temperature is typically near freezing (1–4°C or 34–39°F). Without an insulated suit, hypothermia would incapacitate or kill a person within minutes.

4. Breathing
• Humans cannot breathe at such depths without highly specialized gas mixtures because oxygen becomes toxic under high pressure. A standard air supply would fail due to the compression of gases and other physiological risks.

5. Decompression
• If a diver somehow reached that depth and then attempted to resurface quickly, the rapid change in pressure would cause decompression sickness (commonly known as “the bends”), which can be fatal.

Summary

In reality, surviving at 500 meters underwater without protective equipment and specialized breathing systems is 100% impossible due to pressure, temperature, and physiological constraints. The scene is purely a work of fiction, designed for dramatic effect.

You're absolutely right to question the realism of a 500m dive without a suit! It's **extremely far from reality**, bordering on the physically impossible for an unaided human.

Let's break down why, based on real-world physiology and diving science:

1.  **Pressure:** At 500 meters (1,640 feet), the pressure is approximately **51 atmospheres absolute (ATA)**, or 51 times the pressure at the surface.
    * **Reality:** While the human body is mostly water and incompressible, gas-filled spaces (lungs, sinuses, middle ear) would be crushed. Lungs would collapse, potentially leading to severe barotrauma and death. Without a rigid suit or pressurized environment, survival is impossible.
    * **Movie vs. Reality:** The movie implies the special suit *helps* with the pressure and provides a specialized gas mixture, but the idea of him tearing it off and swimming freely at that depth, even for a short time, is pure Hollywood fiction.

2.  **Breathing Gas:** Normal air (21% oxygen, 78% nitrogen) is toxic at deep pressures.
    * **Reality:**
        * **Nitrogen Narcosis:** Nitrogen becomes increasingly narcotic at depths beyond 30-40 meters, causing disorientation and impaired judgment. At 500m, it would be instantly incapacitating and lethal.
        * **Oxygen Toxicity:** Even oxygen, vital for life, becomes toxic at high partial pressures. At 500m, the oxygen in air would cause immediate central nervous system oxygen toxicity, leading to convulsions, seizures, and death.
        * Deep divers use **Trimix or Heliox** (mixtures of helium, oxygen, and sometimes nitrogen) to manage these risks. Helium replaces nitrogen to reduce narcosis and is less dense, making it easier to breathe at pressure. Oxygen levels are carefully reduced to avoid toxicity.
    * **Movie vs. Reality:** While the movie acknowledges a special gas mix, the *absence* of any breathing apparatus would mean instant death from both oxygen toxicity and nitrogen narcosis, even if the body somehow survived the pressure.

3.  **Cold:** Water at 500 meters is incredibly cold, typically just above freezing.
    * **Reality:** Without a dry suit or heated suit, hypothermia would set in rapidly, leading to loss of dexterity, judgment, and eventually unconsciousness and death. The body would go into cold shock almost immediately.
    * **Movie vs. Reality:** Being in just "boxers" at that depth, as some discussions about the scene suggest, would be an instant death sentence due to extreme cold.

4.  **Decompression Sickness (The Bends):** This is a critical factor for deep dives.
    * **Reality:** When a diver ascends from depth, dissolved inert gases (like nitrogen and helium) come out of solution and form bubbles in the tissues and bloodstream if the ascent is too fast. This causes severe pain, paralysis, brain damage, and death. A 500m dive would require days, if not weeks, of precisely controlled decompression stops in a hyperbaric environment. Even with the special suit, a rapid ascent would be catastrophic.
    * **Movie vs. Reality:** The film *does* show Ethan suffering from decompression sickness and being put in a hyperbaric chamber. This part is surprisingly accurate in acknowledging the consequence, but the idea that he could survive the rapid ascent and then be "healed" in a matter of hours to full fighting fitness is a major stretch. Real-world decompression from such a depth would be a prolonged and delicate process.

**In summary:**

* **Human record for deepest SCUBA dive:** Around 332 meters (1,089 feet) using highly specialized mixed gases and extensive support, with a high fatality rate.
* **Human record for deepest free dive (single breath):** Over 200 meters, but this involves no breathing at depth and is for very short durations.
* **Simulated dives:** While researchers have simulated 500m saturation dives in controlled hyperbaric chambers on land, these involve divers living at that pressure for extended periods, breathing carefully controlled gas mixtures, and undergoing weeks of slow decompression. This is entirely different from an unsuited dive in the open ocean.

The *Mission: Impossible* scene is thrilling cinema, but it's important to remember that it takes extreme artistic license with the laws of physics and human physiology. Surviving 500 meters without a specialized suit and breathing apparatus is fundamentally impossible.