Question

High efficiency particulate air (HEPA) filters have the following characteristic features:
A. They are dry type filter.
B. Non-reusable filter.
C. Remove 99.9 per cent of airborne particles.
D. Remove dust, pollen, mold and bacteria.
Choose the correct answer from the options given below:

• A. A, B and D only
• B. A and B only
• C. A, B, C and D
• D. B, C and D only

Hint:

The key feature of a HEPA filter is its extremely high efficiency (\textbf{99.97% at 0.3 µm}). All other characteristics, like being a dry, disposable filter that captures dust and bacteria, stem from this primary function.

Answer 1

The Correct Option is C

Step 1: Define HEPA filters and their characteristics. Step 1: HEPA filters are a type of mechanical air filter used in environments requiring very clean air, such as operating theatres, clean rooms, and biosafety cabinets.
Step 2: Evaluate each statement.
Step 2:

(A) They are dry type filter. True. HEPA filters are made of a mat of randomly arranged fibers, typically fiberglass, and operate dry.
(B) Non-reusable filter. True. Once a HEPA filter is clogged with particles, it cannot be effectively cleaned and must be replaced.
(C) Remove 99.9 per cent of airborne particles. True. The standard definition of a HEPA filter is one that removes at least 99.97% of airborne particles with a size of 0.3 micrometers (µm). So, removing 99.9% is a correct, though slightly less precise, statement.
(D) Remove dust, pollen, mold and bacteria. True. The filter's high efficiency allows it to capture a wide range of microscopic particles, including all those listed.
Step 3: Conclude which features are correct.
Step 3: All four statements (A, B, C, and D) are characteristic features of HEPA filters.