Glossary / Physical properties
Evaporation rate
Evaporation rate is the speed at which a liquid turns into vapor, normally stated relative to a reference substance such as butyl acetate. A fast-evaporating liquid fills the air with vapor quickly, increasing both inhalation exposure and the chance of forming a flammable atmosphere.
Explanation
Because the number is relative, it only makes sense with its reference. Some SDSs use butyl acetate with a value of 1, so a figure above 1 means the liquid evaporates faster than the reference and a figure below 1 means it is slower. Others use a different reference such as ether, so check which one is being used.
Evaporation rate is connected to Vapor pressure and Boiling point, but it also depends on air movement, surface area and temperature. A shallow open tray in a drafty area evaporates much faster than the same liquid in a closed container. Spreading a liquid thinly, spraying it or heating it speeds evaporation.
The practical effect is on exposure timing. A fast evaporator gives a quick spike of vapor when a container is opened or a spill occurs, so the vapor must be controlled right away. A slow evaporator leaves a liquid film on surfaces for a long time, which can mean prolonged skin contact and a lingering vapor source.
Evaporation can also cool the liquid, and in paint, coating and cleaning products it determines drying time and how much solvent is released into the room. That makes it a factor when selecting products to lower emissions and when planning ventilation for spray or wipe-on tasks.
What to do and watch for
- Keep containers of fast-evaporating liquids closed when not in use.
- Plan ventilation around spraying, wiping and open-tray tasks.
- Check the reference substance before comparing evaporation rates between products.
Where it appears on an SDS
- Section 9: Physical and chemical properties. States the evaporation rate with its reference compound, or marks it as not available or not applicable.
SDS content and wording vary by supplier. This page is general reference and does not replace the current SDS for your product.