The foundation of Haz-Map is information about toxic chemicals. The Chemicals table has 989 records, and each record has more than 50 fields. The fields are used to store information about the properties of the chemical, such as its vapor pressure (a number) and whether or not it is known to cause occupational asthma (yes or no). Because Haz-Map is a relational database, chemicals can be linked to industrial processes, for example, welding, and also to hobbies and other non-occupational activities explored in an occupational history. The bi-directional arrows mean that you can find all processes associated with lead or all chemicals associated with welding.