What is a common characteristic of the dust, stock, and refuse systems prohibited from having energy recovery ventilation?

The correct answer highlights that dust, stock, and refuse systems are associated with the conveyance of materials that may pose an explosion hazard. In environments where such potentially explosive materials are present, the integration of energy recovery ventilation systems could create safety risks. These systems often involve air being drawn from the space and reused or recirculated, which could unintentionally recirculate potentially hazardous dust or gases back into occupied areas. Therefore, prohibiting energy recovery ventilation in these systems is a precautionary measure to prevent the risks associated with the possible explosion of flammable or combustible dust and materials. This focus on safety in environments handling such materials aligns with existing safety regulations and standards to protect the health of occupants and workers.