Why are positive-pressure SCBAs considered preferable to demand apparatus?

Positive-pressure self-contained breathing apparatus (SCBAs) are indeed considered preferable to demand apparatus mainly because they offer more protection against contaminants. This is due to the way they operate.

In positive-pressure SCBAs, the pressure inside the mask is greater than the surrounding atmospheric pressure, which ensures that any inhaled air is less likely to be contaminated by external pollutants. This configuration prevents smoke, toxic gases, and other harmful particulates from entering the breathing zone of the wearer, which is critical in hazardous environments, such as during firefighting operations.

Furthermore, this advantageous design also tends to maintain a seal around the facepiece, reducing the risk of exposure to harmful gases or chemicals during firefighting or rescue operations.

While the other options touch upon various characteristics of SCBAs, they do not capture the fundamental reason why protection against contaminants is a primary consideration when choosing breathing apparatus for hazardous environments. For instance, while comfort and weight may influence usability, the paramount concern in firefighting situations is the health and safety of the firefighters, which is directly improved with the added protection that positive-pressure systems provide.