see also:

• physics
• comparison of gas options for hiking or camping
• gas fittings for camping

• most substances become gases once they have become liquids (at their melting point temperature) and then the temperature exceeds their boiling point temperature
• NB. some substances sublime straight from solid to gas

• this is the temperature at which a liquid will form gas bubbles and start to evaporate into its gaseous form
• the vapour pressure of a liquid rises as its temperature increases
• the boiling point temperature is when the liquid's vapour pressure exceeds that of the pressure of the space above it
• the standard boiling point is measured when the space above it is normal atmospheric pressure of 1 atm
• if the pressure of the space above it falls then the boiling point temperature falls (eg. high altitude)
  • this is why butane gas stoves can work in freezing conditions at high altitude but not at normal altitudes
• if the pressure of the space above it increases, then the boiling point temperature increases (eg. pressure cooker, LPG bottles)
  • vapour pressure of propane is much higher than that of butane and thus propane containers need to be build much stronger
    • see comparison of gas options for hiking or camping for more details

PV = nRT

• where:
  • P = pressure in Pascal (N/m²)
  • V = volume of space the gas is contained within measured in m³
  • n = number of moles of gas substance in mol
  • R = the gas constant = 8.314 J/(mol.K)
  • T = temperature in degrees Kelvin K= Celsius temp + 273.15

• NB. if use P in atm, V in litres, then the gas constant is 0.08206 L.atm/(mol.K)

• the PV product above remains constant as you have not lost any gas, hence:
  • P₂V₂ = P₁V₁
  • ie. the new pressure = P₁V₁ / V₂

• 1 atmosphere (atm) is the standard pressure of earth's atmosphere which equates to:
  • 1.01325 bar
  • 101.325 kPa
  • 760mmHg = 760 Torr
  • 14.696 pounds per square inch (psi)

• in general gas density rises in proportion to its molecular weight for the same temperature and pressure
• the following assumes same temperature and pressure (except for the hot wood fire smoke which is compared to normal ambient air temperature)
• carbon monoxide, like smoke, coming from a stove or heater will initially rise hence smoke alarms and CO alarms should generally be mounted near a ceiling for the earliest warning, later both will mix with air as they cool to air temperatures and smoke may even sink
• underground coal miners are at major risk from:
  • pools of carbon dioxide (“black damp”) as it forms from human respiration, the rotting of timber supports, or the slow oxidation of coal
  • carbon monoxide poisoning via either:
    • “white damp” - CO produced from machinery exhausts or slow coal fires
    • “after damp” - CO left behind after a methane or coal dust explosion
  • methane asphyxiation “firedamp” from methane trapped within coal seams and rock strata that bleed out when mined
  • hydrogen sulphide “stinkdamp” produced by the decomposition of iron pyrites in the presence of moisture or organic breakdown
• NB. fog tends to lie close to ground not because of intrinsic gas density but because it is colder and thus more dense