What defines extra hazard occupancies group 1?

Extra hazard occupancies group 1 is defined by high quantities and combustibility of materials present within the space. This category includes environments where there is a significant amount of combustible content, which may lead to severe fire risks. The inclusion of dust and lint further emphasizes the specific hazards present; these materials not only contribute to the overall combustibility but also can accumulate and create additional risks in the event of a fire.

In contrast, the other options indicate characteristics of occupancies that would not qualify as extra hazard occupancies. For instance, low quantities and low combustibility suggest a lesser risk, while the absence of materials and low to moderate heat generation indicate a more controlled and less hazardous environment. Thus, option B accurately reflects the defining characteristics of extra hazard occupancies group 1, which require specialized fire protection measures due to their inherent risks.