Home Podcasts THMG132 – Vapor Pressure vs. Volatility

THMG132 – Vapor Pressure vs. Volatility

Volatility Ahead Road Warning Sign , 3d render

In this episode, Bob and Mike explore the differences between vapor pressure and volatility.

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Complete Show Notes

5:15 What are Vapor Pressure and Volatility?

  • Vapor pressure:
    • Physical property that can be measured – no chemical change
    • Simply put, it’s the ability of a substance to drive vapor into the air
    • Directly correlates with temperature
  • Volatility:
    • Simply put, it’s the tendency of a substance to vaporize
    • Expresses comparisons in terms of – i.e. [Chemical A] is more/less volatile than [Chemical B]
    • Provides context and perspective

12:45 Measuring Vapor Pressure

  • Can be measured in two ways:
  • We need a standard temperature reference to take an accurate measurement
  • When the vapor pressure and atmospheric pressure is equal, we have boiling
  • When the pressure of vaporization meets the atmospheric pressure, we reach equilibrium
  • We can’t reach equilibrium if the vessel is open – this relates to volatility
    • This is when the rate of evaporation is equal to the rate of condensation
    • Both of these are phase changes and are happening simultaneously

22:45 Vaporization vs. Volatilization

  • In general, heavyweight compounds produce small amounts of vapor
  • Conversely, lightweight compounds produce significant amounts of vapor
  • In closed vessels, pressure might build (volatility) – the higher the pressure inside the closed vessel, the higher the vapor pressure
  • Liquids with low boiling points have high vapor pressures, and liquids with high boiling points have low vapor pressures
  • Bob and Mike recommending having the vapor pressure of a few chemicals memorized (i.e. water or acetone) for reference points

26:15 How Vapor Pressure Impacts Our Decisions and Safety

  • Production of vapors is a major indicator of responder safety
  • Vapor is the physical form of a substance that’s most dangerous for us – inhalation and flammability
  • Vapor pressure affects transportation decisions for responders
  • This is because we may not be able to overpack a liquid with a high vapor pressure if there’s a possibility of the vessel’s pressure becoming too high

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  1. Great podcast, very enlightening! Aside from the relationship between Vapor Pressure and Volitility, what about the relationship between Volitiliity and the distance between a products LEL and UEL?

    • Great point Mark!

      I am trying to find ways to tease out the subtly and nuance of deeper understanding of the Chemical and Physical properties of Hazmat. This is one of them.



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