What safety measure should be taken when working with fuel systems?

Wearing gloves when working with fuel systems is a crucial safety measure because it provides a barrier between your skin and potentially harmful substances such as fuel or chemicals. Gloves can protect against skin irritations, chemical burns, and absorption of harmful substances that may occur if fuel comes into contact with the skin. This precaution is particularly important given that fuels can contain toxic components, and prolonged exposure can pose health risks.

In contrast to the other options, using tools is essential for safely working on fuel systems when used properly, open flames are a significant fire hazard in an environment with flammable substances, and using defective equipment increases the risk of accidents and injuries. Thus, wearing gloves is the correct safety measure that significantly contributes to personal safety in the context of fuel systems.