An area where a hazardous gas has been detected may only be entered by personnel trained in rescue operations and qualified to use a _______.

The correct answer indicates that personnel entering an area where hazardous gas has been detected must be qualified to use a self-contained breathing apparatus (SCBA). This equipment is crucial for safety, as it allows individuals to breathe in environments where breathable air may be compromised due to the presence of toxic gases or low oxygen levels. The SCBA provides a supply of clean, breathable air independent of the surrounding atmosphere, thereby protecting users from inhaling harmful gases while they conduct rescue operations.

It's essential for crews potentially working in hazardous areas to be well-prepared and equipped with the appropriate gear to ensure their safety and effectiveness. While measuring devices like combustible gas indicators or flame ionization indicators can help monitor gas levels, they do not provide the necessary respiratory protection to enter an area filled with potentially dangerous gases. Similarly, while fire suppression kits are important for managing fires, they do not address the immediate concern of personal breathing needs in an oxygen-deficient or toxic environment. Hence, the use of an SCBA is a critical requirement for safe entry into such situations.