The purpose of a mask is to filter droplets containing microorganisms expelled from the mouth. What is another purpose for the mask?

a. It's a good idea to wear two masks for better protection.
b. Many masks filter about 99% of particulate matter larger than 5 mm.
c. Masks are still effective if they become moist.
d. Reusable cotton masks are still appropriate.

ANS: B
Many masks filter about 99% of particulate matter larger than 5 mm but only about 45% to 60% of particles 0.3 mm in diameter. Special masks for aerosolized particles such as laser or TB are fitted for each employee. Wearing double masks forms a barrier instead of filter and may cause expulsion of particles to escape from the cheek folds.