Working with Benzene program explains the various measurements of contaminants and the hazards of Benzene with emphasis on safety. Before we discuss chemicals and hazardous materials, it's important to understand some basic terms. You may or may not be familiar with these terms, but if you handle, use, store, or dispose of chemicals and hazardous materials, it's very important to understand the terminology. The health effects of any toxic substance are related to the amount of exposure, also known as ”dose.” The greater the dose the more severe the effects. Some chemicals can cause toxicity at very low doses. Parts per million (PPM) is a familiar term to anyone working with chemicals and toxic materials. It is important to understand how very small amounts of toxicity are measured.