Which of the following describes a HEPA filter and its typical use in occupational hygiene?

• A. A filter that has 99 percent efficiency at 0.1 micrometers and is used only in consumer air purifiers.
• B. A filter with at least 99.97 percent efficiency at 0.3 micrometers and is used in containment and clean environments.
• C. A filter that removes 95 percent of particles at 1 micrometer and is used in general ventilation.
• D. A filter with 90 percent efficiency at 5 micrometers and is used in dusty workplaces.

Answer: (B)

HEPA filtration is defined by its extremely high capture efficiency for small particles, with a standard rating of at least 99.97% removal of particles at 0.3 micrometers. That size is considered the most penetrating for these filters, so achieving 99.97% at this point means the filter performs very well across a broad range of particle sizes because particles smaller or larger than 0.3 μm are captured even more effectively through diffusion and interception. In occupational hygiene, HEPA filters are used in containment and clean environments to minimize airborne exposures and protect both workers and products, for example in containment hoods, clean benches, cleanrooms, and other controlled ventilation areas. The other descriptions don’t match the standard HEPA rating or typical applications.