- 100% helium - brown cylinders at 13,700kPa
- Heliox - 79% helium and 21% oxygen - brown cylinders with white shoulders
Helium
Helium
- Helium is a colourless, odourless, tasteless, inert gas
- It lacks valent electrons (valence = 0) which makes it inert
- Extremely scarce in Earth's atmosphere (0.00052%); present in natural gas in concentrations up to 7%
- Manufactured by:
- Liquefaction of air or natural gas
- Removal of easily condensable fractions
- Adsorption of contaminant gases
- Low density (and therefore specific gravity) vs. oxygen and air
- Similar viscosity to air
- This increases the propensity for laminar flow according to Reynold's number (Re = pwd/η)
- This reduces work of breathing and increases oxygenation
- Work of breathing is directly proportional to gas flow during laminar flow
- Work of breathing is proportional to the square of gas flow during turbulent flow
- This is most effective in larger, upper airways
- In the smaller distal airways, flow is predominantly laminar anyway
- Therefore resistance is related to gas viscosity (Hagen-Poiseuille) rather than density
- Therefore Heliox is relatively ineffective at improving gas flow properties
| Gas | Specific gravity |
| Air | 1.0 |
| Oxygen | 1.091 |
| Heliox | 0.337 |
| Helium | 0.178 |
- To improve oxygenation in airway obstruction
- Typically stenotic lesions around the glottis e.g. infection (epiglottitis, laryngitis), foreign body, tracheal stenosis
- In laser surgery around the airway to reduce flammability of breathing mixture, as it doesn't support combustion
- MRI: superconducting magnet within the MRI scanner is cooled to near absolute zero by immersing it in liquid helium, reducing electrical resistance
- Diving: Used for avoiding nitrogen narcosis in deep water diving
- Rockets: cleaning engines, pressurising liquid fuel, condensing hydrogen and water to make rocket fuel
- Party tricks: produces higher frequency vocal sounds