With an increasing number of airborne pollutants finding their way into our homes, HEPA air purifiers have become families\' first line of defense against irritants that can cause both acute and long term health conditions. Here are 7 answers about these powerful air cleaners that are both interesting and helpful.

What does HEPA mean? It is an acronym for high efficiency particle arresting. Using the first letter of each word reduces the space and time it takes to write or talk about it, and yet the acronym accurately identifies the technology.

How does it work? It works by pulling air through a filter whose openings are so small that it traps particulates as small as .3 microns with a micron being defined as one millionth of a meter. It should have a high capacitor motor that allows it to run safely and efficiently 24 hours every day.

Here is the micron count for some common items. A postage stamp that is one inch high is 25,400. Pollens are 2 to 1000. Beach sand is 100 to 2000. Bacteria are .5 to 20. Human hair is 40 to 300. Mold spores average 10 to 30.

What kinds of pollutants can it eliminate? These cleaners are incredibly efficient at removing household dust, dust mites, mold and mildew spores, pollen, pet dander from all warm-blooded animals, bacteria, and viruses.

What is their efficiency rate? By definition they are able to remove 99,997 out of every 10,000 invisible to sub-micron size particles with 99.97% efficiency. This means that for every 10,000 particulates suspended in the air, it will remove 99,997 down to .3 microns in size leaving only 3 out of every 10,000 particulates.

Can it eliminate odors? While not particularly effective at removing odors, when combined with an additional filter that does remove odors, it packs a powerful punch against indoor pollutants, and creates indoor air that is virtually free from particulates and odors.

How is it able to remove viruses since they are smaller than .3 microns? While the size of viruses is smaller than .3 microns, they tend to piggy back on larger airborne pollutants found in indoor air. So by removing these larger particles, the cleaner is in fact removing viruses as well. This makes elimination much easier than their size would indicate.

How long do the filters last? A filter that does not have pre-filters will only last for 6 months or so depending on the number of particulates it removes from the air, and this number varies greatly from one home to another.

A filter that has several pre-filters can last as long as 5 years because they are designed to trap the larger particles that you can see such as hair and dust to prevent them from clogging the HEPA filter. The purifiers whose filters last the longest contain several pre-filters.