Basic characteristics of an SCBA backpack harness assembly include which of the following?

The correct answer highlights the essential features of an SCBA (Self-Contained Breathing Apparatus) backpack harness assembly. A rigid frame is crucial for providing structural integrity and stability to support the complete system and allow firefighters to move effectively while wearing the equipment. The adjustable straps are vital for customizing the fit to accommodate various body shapes and sizes, ensuring comfort and security during use. This design allows for quick adjustments, enabling each user to attain a snug and supportive fit, which is necessary for maintaining balance and minimizing fatigue, especially during strenuous activities.

Other characteristics mentioned in the options, such as adjustable head straps or elastic waist straps, may not apply universally across all SCBA designs and do not encapsulate the fundamental structure and support role that a rigid frame with adjustable straps provides. Lightweight design can be beneficial, but it is not a defining characteristic of the harness assembly itself; rather, it pertains to the overall assembly's usability and comfort in various scenarios. This distinction is why the selection of the rigid frame and adjustable straps is the most accurate answer to reflect the basic characteristics installed within SCBA systems.