What does a positive and negative user seal fit check primarily confirm?

A positive and negative user seal fit check primarily confirms that the respirator is correctly seated on the face. This process ensures that there are no leaks around the edges of the respirator, which is crucial for the effective functioning of the device. If the respirator does not fit properly, contaminants can enter through gaps, rendering the protection it offers ineffective. The fit check also verifies that the respirator is creating a proper seal with the user's facial contours, thereby enhancing safety while wearing it in environments with airborne hazards.

The other options, while related to respirator use, do not specifically pertain to the primary intent of the seal fit check. Durability of the respirator, duration of wear, and performance in various environments do not address the immediate concern of ensuring a proper fit to maximize protection during use.