A vapor density is also usually listed. This indicates whether the vapor will drop to the floor or disperse widely through the air. Section III provides fire and explosion data. Flash point indicates the temperature at which the mixture will spontaneously burst into flames when heated. The lower explosive limit is the percentage of material in the air at which there may be an explosion if a spark occurs.
Painters commonly wear alarms to assure they remain well below the lower explosive limit.
Should a fire occur, special firefighting precautions are provided in this section, along with the recommended extinguisher media. Water tends to be a poor extinguishing medium for organic chemical fires. Section IV provides special information concerning chemical reactivity. Gunpowder, for instance, would be listed as a reactive chemical. Many chemicals will have less obvious reactivities, and will be listed in this section.