The following questions can be answered by reading an MSDS, although not all questions apply to all chemicals. The TLV is a term used to express how much of a substance in the air nearly everyone can be exposed to day after day, without adverse effects. The most allowed are four such periods in a workday, with at least 60 minutes between exposure periods, as long as the TLV-TWA is not exceeded. Unfortunately, because most chemicals have not been tested for their long-term health hazard, reproductive effects or potential to cause cancer, these PEL and TLV descriptions merely serve as warnings. This is important for people concerned with shipping, storing and disposal.
Vapor pressure is the pressure of gas at the surface of a liquid that is evaporating.
Gasoline, for example, evaporates easily. Sometimes you can see it evaporating as you fill your cars gas tank. Liquids that evaporate easily are worrisome because vapor can build up around you quickly. It is a particularly big problem in confined spaces. The lower the boiling point of a substance, the higher its vapor pressure.