Thursday, May 15, 2008

Low Cost Shelter Ventilation Filter

If you have ever thought about building a fallout shelter/safe room you know one of the major expenses is the ventilation system. Without it you would suffocate in a concrete tomb. The heart of the system is a good quality HEPA filter to keep out the radioactive dust.

Since these filters are not cheap, I wanted to find something that would work just as well for a low cost. I see 2 options. The 1st one is to use the air filter assembly off of an automobile engine. These filters are made to keep small particulants out of your engine.

If you take 2 or more of these filters and glue them together with some silicone, you can make a vary large filter quite easily. Large V8 engines will breathe over 650cfm, which should be more than adequate for most smaller shelters, so choose a filter for one of these. Anything over 350ci should be sufficient.

If you build a box to house it in, you can create a prefilter out of furnace filters. Build it fancy or not, you can staple, glue, slide fit; whatever it takes to attach them. Personally, I would build it so they could be replaced easily in case they plug up.

The next best option would be an oil bath air cleaner from an old diesel engine. You can get these from old farm equipment such as combines, balers and tractors.

These types of filters were also used on emergency vehicles when Mt. St. Helens blew it's top. They did just fine filtering out the ash, protecting the engines from the grit.

Choosing a proper fan is critical as not just any fan will do. You need one that is designed to work against a static pressure as they are built differently than fan motors that just blow air, like your common box fan. Here is one that will work for this purpose:

With a little bit of ingenuity this can be incorporated into your ventilation system and you will have an inexpensive solution to filtering your shelters air.

This could be also used to filter air for a safe room, but for that you may need the HEPA filter. I looked on FRAM's website but could find no details on how small of particles their air cleaner will filter. The oil bath method should work fine though they are a little harder to come by.

For extra protection against Biological and Chemical attack, create a prefilter of activated charcoal to absorb these agents before they hit your main filter.

Use furnace filters and hardware cloth to create a "cage" to hold the charcoal in. Be sure that it will fit around your auto filters, or create a prefilter box through which your system will draw air and fill it with the charcoal.

AlphaRubicon has some great info on this which was some of my inspiration to come up with this solution. Much of their info is for members only, but they have some valuable stuff available to the public at large.


  1. Nice -

  2. Just wanted to let you know that has high quality HEPA filters listed for $109 or $129 with a pre-filter. This might be a good way to go if someone doesn't want to messs with the car filters. This supplier can bw found on the Steve Quayle web site.

  3. Such a system could indeed work quite well. Certainly better than no filter at all. This has got me to thinking about natural filtration methods one could us if caught without one already in place.

  4. Don't forget about filtering the other way.

    The stealthiness of your shelter would be ruined if a random passer-by smelled cooking odors, or tobacco odors, etc.

  5. HEPA - High Efficiency Particulate Air A filter which can remove 99.97% of all particles down to .3 microns in size. Micron - one millionth of a meter. Good thought but automotive filters will not provide the protection needed for radiological/biological problems. They will work fine as pre-filters but that is the extent of it. I would nix the oil bath as drawing your breathing air through it will add oil vapor to your air. Not a good idea, plus it may make your shelter atmosphere combustible.

  6. Excellent information,
    Its very useful for me. Air which comes through the openings of the buildings gets heated and circulates in the atmosphere with dusts and gaseous particles. Thanks
    Air Ventilation