The size of the SCBA unit primarily affects:

The size of the SCBA (Self-Contained Breathing Apparatus) unit primarily affects mobility because it directly influences how easily a firefighter can move and maneuver while wearing the device. A larger, bulkier SCBA may restrict movement, making it more challenging to navigate through tight spaces or perform physical tasks effectively during firefighting operations or rescues. Conversely, a smaller, more compact unit would enhance mobility, allowing the wearer to operate more freely and efficiently in various environments.

While other factors such as durability, cost, and air quality are important considerations when selecting an SCBA, they are not primarily impacted by the size of the unit. Durability relates more to the materials and construction of the SCBA rather than its size. Cost concerns typically depend on the technology and features included in the unit rather than its dimensions. Air quality relates to the filtration and oxygen delivery systems within the SCBA, which are independent of the physical size of the apparatus itself. Thus, mobility is the factor most influenced by the size of the SCBA unit.