Final answer:
Hazardous materials are primarily a contact hazard in the liquid state, as they spread over surfaces and maintain constant contact, allowing for easy transfer of contaminants.
Step-by-step explanation:
Hazardous materials can pose different types of dangers depending on their state of matter. When considering the primary hazard regarding contact with a substance, we need to think about the physical properties of solids, liquids, and gases. Solids maintain a fixed shape and volume, where the particles are tightly packed together, but not necessarily a contact hazard. Gases expand to fill their container and are not constantly in contact with surfaces in a way that typically constitutes a contact hazard. Liquids, however, are of particular concern for contact hazards because, while they flow freely, they have a definite volume and maintain constant contact with surfaces, which can lead to continuous exposure to the hazardous material.
Therefore, the state where hazardous materials are primarily a contact hazard is when they are in the liquid state. This is because liquids have the capacity to spread over surfaces and through their state of constantly being in contact, can transfer contaminants easily upon touch.