Unit
- Boyle's Law: At constant temperature, the volume of a gas varies inversely with pressure. This explains why air spaces in the body (sinuses, lungs, ears) change volume during ascent and descent. Failure to equalize can cause barotrauma.
- Dalton's Law: The total pressure of a gas mixture equals the sum of partial pressures of each component gas. Partial pressure of oxygen and nitrogen increases with depth, affecting gas exchange and toxicity risks.
- Henry's Law: The amount of gas dissolved in a liquid is proportional to the partial pressure of that gas in contact with the liquid. This governs how inert gases dissolve in tissues during a dive and come out of solution during ascent.
- Inert Gas Narcosis: Nitrogen under increased partial pressure causes a narcotic effect similar to alcohol intoxication. Symptoms include euphoria, impaired judgment, and motor skill reduction, typically starting around 30 meters (100 feet).
- Oxygen Toxicity: Breathing elevated partial pressures of oxygen can lead to central nervous system toxicity (convulsions) and pulmonary toxicity (lung damage). Limits are based on exposure duration and depth.
- Pressure-Volume Relationships: The greatest volume change occurs near the surface (first 10 meters). That is why rapid ascents from shallow depths can still cause serious lung overexpansion injuries.
- Implications for Decompression: During ascent, dissolved inert gas forms bubbles if decompression is too rapid. Bubble formation can lead to decompression sickness. Adherence to decompression schedules prevents this.
- Management Application: Dive medicine coordinators must understand these laws to educate divers, implement safety protocols, and recognize early signs of gas-related disorders.
- Gas Density and Breathing Resistance: As depth increases, gas density rises proportionally with ambient pressure. Higher density increases airway resistance and the work of breathing, which can lead to carbon dioxide retention and reduced exercise tolerance. This effect is especially significant beyond 30 meters and in cold water conditions.
- Cumulative Oxygen Exposure: Oxygen toxicity risk depends on both depth and cumulative exposure time. The Central Nervous System Oxygen Toxicity Clock tracks exposure using established depth and time limits. Exceeding these limits increases seizure risk, particularly during exercise, stress, or in cold environments.
- Dive Profiles and Bubble Dynamics: The risk of decompression sickness is influenced by both dive depth and duration. Short deep dives produce fast inert gas saturation in tissues, while longer shallow dives allow equilibration. Ascent rates and safety stops must be tailored to the specific dive profile.
Scope of Practice
Role: Dive Medicine Coordinator
Within scope:
- Delivering pre-dive briefings on gas law concepts and equalization techniques
- Recognizing symptoms of inert gas narcosis and oxygen toxicity during dives
- Recommending ascent rate limits and safety stops based on dive tables
- Maintaining emergency oxygen equipment for first response
- Documenting diver profiles and exposure histories
Outside scope:
- Diagnosing neurological decompression illness or arterial gas embolism
- Prescribing treatment tables or recompression chamber settings
- Performing invasive procedures such as intravenous lines or catheterization
- Providing definitive medical clearance beyond fitness screening
- Operating hyperbaric chambers without proper certification
Quick Revision
- Boyle's Law explains barotrauma risks from volume changes in air spaces.
- Dalton's Law relates depth and partial pressures of breathing gases.
- Henry's Law governs inert gas uptake and elimination, key to decompression theory.
- Inert gas narcosis and oxygen toxicity are depth- and time-dependent risks.
- Dive medicine coordinators apply gas law knowledge in education and prevention.