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Breathing gas mixtures such as trimix and heliox include helium, which can also cause decompression sickness. Helium both enters and leaves the body faster than nitrogen, so different decompression schedules are required, but, since helium does not cause narcosis, it is preferred over nitrogen in gas mixtures for deep diving. [59]
In 2011, a large Danish epidemiological study found an increased risk of lung cancer for people who lived in areas with high nitrogen oxide concentrations. [197] Another Danish study, likewise noted evidence of possible associations between air pollution and other forms of cancer, including cervical cancer and brain cancer. [198]
Alternative assumptions for the extrapolation of the cancer risk vs. radiation dose to low-dose levels, given a known risk at a high dose: supra-linearity (A), linear (B), linear-quadratic (C) and hormesis (D). The linear dose-response model suggests that any increase in dose, no matter how small, results in an incremental increase in risk.
Radioactive contamination, also called radiological pollution, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids, or gases (including the human body), where their presence is unintended or undesirable (from the International Atomic Energy Agency (IAEA) definition).
An assessment of the burden of disease potentially resulting from ELF MF exposure in Europe found that 1.5–2% of childhood leukaemia cases might be attributable to ELF MF, but uncertainties around causal mechanisms and models of dose-response were found to be considerable. [24]
Depending on the proportions of helium and nitrogen, these gases are called heliox if there is no nitrogen, or trimix if there is nitrogen and helium along with the essential oxygen. [ 33 ] [ 34 ] The inert gases used as substitutes for nitrogen have different solubility and diffusion characteristics in living tissues to the nitrogen they replace.
The dry air on the Earth we inhale consists of 78.8% nitrogen, 20.95% oxygen and 0.93% argon. Heliox therapy is substitution of nitrogen with helium. Helium itself has no pharmacological value, it does not react in the body. Its only purpose is to make the flow less turbulent and help oxygen to get into the lungs.
The risk of breathing asphyxiant gases is frequently underestimated leading to fatalities, typically from breathing helium in domestic circumstances and nitrogen in industrial environments. [12] The term asphyxiation is often mistakenly associated with the strong desire to breathe that occurs if breathing is prevented.