Page 27 - Test

Section 3: Physical Data

1. Physical State: At room temperature, is the controlled product a liquid, solid, or gas? It
is important to know its normal state at room temperature to predict the response of the
product to a change in temperature and pressure. It is also useful to know how the
product should appear.

For example
When propane is used at room temperature as a heat source,
it works well as the vapour is burned. At 42C propane becomes a liquid, producing
little or no vapour.

2. Odour and Appearance: Odour includes quality of odour (e.g. fruity, sharp, sweet),
intensity (e.g. strong, weak, mild), and irritant properties (pleasant, unpleasant).
Appearance refers to colour (including colourless), surface texture (e.g. greasy, waxy,
soft), and degree of aggregation (e.g. flakes, granules). Liquids can be described by
their viscosity (e.g. thick, thin, gel-like).

3. Odour Threshold: This is the lowest concentration of a chemical in the air that an
average person can smell; it is normally expressed in ppm (parts per million). Some
chemicals have “warning properties”, that is, you can smell the chemical at a much
lower concentration than its allowed exposure limit (e.g. toluene). Others have poor
warning properties, that is, you’d be over-exposed before you could smell the chemical
(e.g. toluene di-isocyanate). Some chemicals have no odour at all (e.g. carbon
monoxide).

Note that chemical cartridge respirators can only be used for chemicals that have good
warning properties. When you smell the chemical through the respirator, it is time to
change the cartridge. For chemicals with either poor or no warning properties, a
supplied air respirator is required.

4. Vapour Pressure: Vapour pressure is one measure of the ability of substances to form
vapours. It refers to the pressure exerted by the material in a vapour state in a closed
container at a given temperature. Materials with a high vapour pressure tend to
evaporate more readily than those with a low one.

5. Vapour Density: Vapour density deals with the weight of the vapour or gas – is it
heavier or lighter than air? Products lighter than air have a vapour of less than one (e.g.
helium, methane), while those heavier than air have densities greater than one (e.g.
chlorine, carbon dioxide). Vapour density is useful in planning air monitoring and
ventilation systems.

Materials which are lighter than air (vapour density <1) tend to rise while heavier
materials tend to fall. However, remember the tendency of a gas to rise or fall depends
not only on density, but also on temperature, air turbulence, and time. In normal
circumstances a gas released into air will eventually mix evenly with it.

6. Evaporation Rate: This is the rate at which a particular material will evaporate relative
to butyl acetate. (Butyl acetate is considered “1”). A rate of
 Over 3.0 is a fast evaporation rate
 0.8 – 3.0 is medium
 <0.8 is slow

A material that evaporates quickly can be more of a hazard to your health (from
breathing more vapours) and be a serious fire hazard than one that evaporates slowly.

AMHSA 25