Which component is not necessary for making a blank in the NIOSH7400 method?

In the NIOSH 7400 method, making a blank is a critical step to ensure that the sampling process yields accurate results. A blank sample helps to determine if there is any contamination or background asbestos fiber that might interfere with the analysis of actual samples.

The process of making a blank involves critical procedures, and sealing the cassette is not necessary for this purpose. In fact, while preparing a blank, it is essential to leave the sampling cassette open to the environment without any fibers being collected. This allows for a verification of the internal environment free from asbestos contamination during the sampling process.

Consequently, the other components mentioned—opening both ends of the cassette, keeping it in a clean area, and ensuring it is not exposed during any sampling—are all relevant and necessary steps for ensuring reliable results when analyzing for asbestos.

Therefore, the option stating that sealing the cassette is not necessary aligns with the correct understanding of how blanks are prepared in the context of the NIOSH 7400 method.