Which of the following are true regarding a membrane-type humidifier?

1. Water and gas are separated by a hydrophobic membrane.
2. The membrane is permeable to water vapor but not to liquid water.
3. As with other passover humidifiers, there is no bubbling action.
4. A small layer of liquid water remains on both sides of the membrane.
a. 1 and 3 only
b. 1, 2, and 3 only
c. 3 and 4 only
d. 2, 3, and 4 only

ANS: B
A membrane-type humidifier separates the water from the gas stream by means of a hydrophobic membrane (Figure 38-3). Water vapor molecules can easily pass through this membrane, but liq-uid water (and pathogens) cannot. As with the wick-type humidifier, bubbling does not occur. Moreover, if a membrane-type humidifier were to be inspected while it was in use, no liquid wa-ter would be seen in the humidifier chamber.