Nitrogen gas (N₂) is a natural and abundant component of the air humans breathe every day. It is a colorless, odorless, and tasteless gas at standard temperatures and pressures. While nitrogen is not inherently toxic, it becomes extremely dangerous under specific conditions. These hazards stem from its physical properties, allowing it to displace oxygen or cause physiological harm when forced into body tissues under intense pressure.
Nitrogen as a Non-Toxic Component of Air
Nitrogen makes up approximately 78% of the Earth’s atmosphere, making it the most plentiful gas we inhale. In this normal atmospheric state, the gas is biologically inert and poses no threat to human health. When inhaled, nitrogen enters the lungs, but its chemically stable structure prevents it from reacting with the body’s internal systems. The gas simply passes across the lung membranes, dissolves minimally, and is then exhaled unchanged. Nitrogen acts as a harmless diluent for the approximately 21% oxygen required for cellular respiration.
The Danger of Simple Asphyxiation
The primary danger of nitrogen gas occurs when it is present in high concentrations, typically above 80%, creating a physical hazard known as simple asphyxiation. This danger is not due to chemical poisoning, but rather the rapid physical displacement of oxygen in the breathing atmosphere. If the oxygen concentration falls below 19.5%, the environment becomes oxygen-deficient, preventing the body from absorbing the required amount of oxygen.
A particular hazard is that pure nitrogen is undetectable by human senses; it is colorless, odorless, and non-irritating. This lack of warning means an exposed person does not experience the normal feeling of breathlessness, which is triggered by rising carbon dioxide levels, not low oxygen. In an environment composed of nearly 100% nitrogen, a person can lose consciousness within one to two breaths. Unconsciousness results from acute hypoxia, where the brain is deprived of oxygen, leading quickly to brain damage and death. This risk is often encountered in industrial facilities that utilize nitrogen to create an inert atmosphere, such as food packaging plants or chemical refineries.
Effects of Nitrogen Under High Pressure
Nitrogen presents a different set of hazards when its pressure significantly increases, such as in the deep-sea environment experienced by scuba divers. According to Henry’s Law, the amount of gas that dissolves into a liquid is proportional to its partial pressure. As a diver descends, the increasing pressure causes more nitrogen to dissolve into the blood and fatty tissues.
This dissolved nitrogen causes a reversible condition known as nitrogen narcosis, often described as an intoxicating effect similar to alcohol consumption. Narcosis typically becomes noticeable at depths greater than 100 feet (about 30 meters), impairing judgment, memory, and motor skills. A more severe risk is Decompression Sickness (DCS), commonly called “the bends,” which occurs during a rapid ascent. If the pressure reduction is too fast, the nitrogen dissolved in the tissues cannot be safely off-gassed through the lungs, causing it to form bubbles. These nitrogen bubbles can obstruct blood flow and physically damage tissue in various parts of the body, including the joints, spinal cord and brain.