Heat moisture exchanger filter

A heat moisture exchanger incorporating a standard high efficiency particulate air

(HEPA) filter has a pore size as small as or smaller than all of the following

pathogens, EXCEPT which one?

a) Mycobacterium tuberculosis

b) Staphylococcus aureus

c) Legionella pneumophilia

d) Mycoplasma pneumoniae

e) Pseudomonas aeruginosa

Answer: d

Explanation

A standard HEPA filter is tested to ensure a 0.3 μm pore size. At this size, protection is

not just about the sieve effect of the filter pore size as electrostatic attraction also has an

important role. Mycobacteria tuberculosis are 0.2 to 0.4 μmwide and 2 to 4μmin length. It

is thought that aHEPAfilterwould still be protective against tuberculosis. Staphylococcus

aureus are about 0.6 μm in diameter. Legionella pneumophilia are 0.5 to 1.0 μm wide and

1.0 to 3.0 μm long. Mycoplasma pneumoniae are the smallest known free-living organisms

and can be as small as 0.15 μm. Pseudomonas aeruginosa are 1 μm by 3μm in size.