Which of the following is a critical safety precaution when using dry chemical extinguishing systems?

Wearing protective gear appropriate for chemical exposure is vital when using dry chemical extinguishing systems. This precaution ensures the safety of individuals operating or responding to a situation involving these systems. Dry chemical agents can be harmful if they come into contact with skin, eyes, or if inhaled. Proper protective equipment such as gloves, goggles, and masks helps to mitigate the risks associated with chemical exposure and ensures that personnel can effectively respond to emergencies without risking their health.

The other options do not align with safety best practices. For instance, allowing unauthorized personnel to be present can lead to chaos or mishandling of the extinguishing systems, which can further complicate an emergency response. Using only a specific brand of extinguishing agent may not be practical, as effective dry chemicals can vary; thus, the focus should be on performance rather than brand loyalty. Blocking access to the control panel not only hinders the effectiveness of the system during an emergency but also poses a risk, as authorized personnel may need access to operate the system efficiently.