Which of the following is considered harmful to aircraft tires?

The correct answer emphasizes that electrical equipment can indeed pose a risk concerning aircraft tires, particularly in the context of maintenance and safety procedures. While electrical equipment itself may not directly damage tires, the processes associated with its use can lead to unsafe conditions. For example, if not properly managed, electrical equipment could cause sparks or heat that may degrade tire materials or impact maintenance practices.

In contrast, low humidity typically does not harm aircraft tires; rather, it could be considered beneficial as high humidity can contribute to issues like corrosion on metal components. Fuel, although it can be a hazard if spilled, does not inherently damage tires unless there's prolonged contact, which might cause degradation depending on the tire material. Solvents may have the potential to harm tires if they are corrosive or if they affect the rubber composition, but the immediate associations with tire integrity raise more serious concerns with electrical equipment usage around them. Thus, caution is warranted in their presence during maintenance activities, primarily related to sparks and heat generation.