Heliox – A Breathing Gas for Deep Dives


Heliox is a specially formulated breathing gas consisting of a mixture of helium and oxygen. It is specifically designed for use in deep-sea scuba diving and commercial diving applications. Due to the unique characteristics of helium, heliox has become an indispensable tool for divers venturing into the depths of the ocean, enabling them to work and explore at depths that would otherwise be impossible with traditional air mixtures. This article will provide an overview of heliox, discussing its composition, history, applications, advantages, and safety considerations.


Heliox is a synthetic blend of helium and oxygen, with the ratio of the two gases varying depending on the specific dive requirements. The most common mixtures are 80% helium and 20% oxygen (Heliox 20/80), 50% helium and 50% oxygen (Heliox 50/50), and 30% helium and 70% oxygen (Heliox 30/70). The exact proportions of helium and oxygen are determined by factors such as dive depth, duration, and individual diver needs.


Heliox was first developed in the 1930s as a means to overcome the limitations of using standard air for deep-sea diving. Early experiments conducted by the U.S. Navy showed that divers breathing heliox could successfully reach greater depths and remain submerged for longer periods without experiencing the debilitating effects of nitrogen narcosis and decompression sickness (also known as “the bends”). The pioneering work of researchers such as Albert R. Behnke and Edgar End laid the groundwork for the development and adoption of heliox in both military and civilian diving applications.


Heliox is primarily used in deep-sea diving operations, particularly those that require divers to work at depths greater than 130 feet (40 meters). These applications include:

  1. Commercial diving: Heliox is used by professional divers engaged in underwater construction, maintenance, salvage, and inspection tasks. These operations often involve significant depths and prolonged exposure to high pressures, making heliox an essential component for diver safety and productivity.
  2. Scientific research: Researchers studying deep-water marine environments and ecosystems rely on heliox to conduct underwater experiments, collect samples, and observe marine life in situ.
  3. Military and special operations: Heliox enables naval and special forces divers to perform covert reconnaissance, search and recovery, and demolition missions at extreme depths.
  4. Technical and cave diving: Advanced recreational divers use heliox for deep technical dives, such as exploring shipwrecks, submerged caves, and other challenging environments.


Heliox offers several significant benefits over traditional air mixtures for deep diving:

  1. Reduced narcosis: Nitrogen, the primary constituent of air, can cause nitrogen narcosis, a dangerous condition that impairs cognitive function and motor skills at depths beyond approximately 100 feet (30 meters). Helium, on the other hand, does not produce narcotic effects, allowing divers to maintain mental clarity and physical coordination at greater depths.
  2. Decreased gas density: Heliox has a lower density than air, which reduces the work of breathing and minimizes the risk of pulmonary barotrauma, a potentially life-threatening condition that can occur during rapid ascents.
  3. Improved decompression profiles: Heliox allows for more efficient off-gassing of inert gases during ascent, reducing the risk of decompression sickness.

Safety Considerations

While heliox offers many advantages for deep diving, it also presents unique safety concerns that divers must address:

  1. Oxygen toxicity: The elevated partial pressure of oxygen in heliox mixtures can lead to oxygen toxicity, a dangerous condition that can cause seizures and unconsciousness. Divers must carefully monitor their oxygen exposure to minimize this risk.
  2. Hypothermia: Helium has a high thermal conductivity, which can increase heat loss and the risk of hypothermia during prolonged dives. Divers must take precautions such as using specialized exposure protection and employing heated undergarments to maintain adequate body temperature.
  1. Voice distortion: Helium alters the resonance of the human voice, making communication between divers more challenging. Divers must rely on specialized underwater communication systems and develop alternative means of communication, such as hand signals or slate writing.
  2. Gas management: Heliox is more expensive than traditional air and requires specialized equipment for blending, storage, and delivery. Divers must be diligent in monitoring their gas supply and planning their dives to ensure they have sufficient gas to safely complete their mission.
  3. Training and certification: Diving with heliox requires specialized training and certification to ensure divers have the necessary skills and knowledge to manage the unique risks associated with deep diving and the use of heliox as a breathing gas. Many diving organizations offer technical and commercial diving courses that include heliox training and certification.


Heliox has revolutionized deep-sea diving, enabling divers to explore the depths of the ocean with greater safety and efficiency than ever before. Its unique properties provide valuable advantages in terms of reduced narcosis, decreased gas density, and improved decompression profiles, making it an essential tool for many commercial, scientific, military, and technical diving operations. However, the use of heliox also presents unique safety considerations that divers must address through careful dive planning, specialized equipment, and comprehensive training. As a result, heliox has become an indispensable component of modern deep diving, allowing divers to push the boundaries of underwater exploration and work while minimizing the risks associated with extreme depths.