3. Examples of criteria for assigning hazards to substances

Let's look at a simple example, that of the "Flammable liquids" class, comprising three categories in the CLP/SGH. To understand which criteria determine the allocation of a category, we need to remember that in the combustion of a liquid, it is not the liquid itself that reacts with the oxygen in the air, but its vapors that exist above the liquid's surface. The volatility of a liquid substance is therefore an important parameter. What's more, once combustion has taken place, heat is released to promote evaporation of the liquid. The two physical parameters chosen are :

• flash point (FP): minimum temperature above which the liquid emits vapours in such quantities that ignition is possible under the effect of an external energy source (flame, spark);

• boiling temperature (T _éb ...