I know best to buy and safest Just in case there is nothing more to buy. How can you make a hepa filter and how to test it ?
I tape a cheap 20x20 inch air filter to a 20 inch box fan. It gets covered with dust after a week. Not really hepa.
What are you filtering? Volume of air would alter design possibilities greatly. If it's something hazardous that you want to filter you need some method of measuring the effectiveness of the filtering. How do you do this? Draw straws? Marines don't fool around with testing equipment. Just disarm and unmask the smallest guy first since if there are still contaminants in the air they'll affect someone small sooner. If he needs to be evacuated he's also the lightest to carry. I can make light of this, but filtering lots of things is deadly serious business. Need more details, since lots of filtering techniques would just result in additional hazmat/contamination.
A HEPA filter is a particulate filter above 99% efficiency. It would be almost impossible to make, and they have such pressure drop that considerable fan horsepower is needed to move any significant air across it. For filtering dust and particulates, 3 of the 3-M pleated filters back-to-back will do a pretty good job. For organic compounds you need charcoal and lots of it, to minimize any bypass of the compounds around the charcoal. For inorganic compounds, special filter composition is needed dependent on the contents of the compounds to be filtered. For example, a charcoal filter will remove the smell of gasoline but not all of the compounds used in the manufacture of the gasoline. Then there is the disposal. Many workers have contracted diseases or poisoned themselves and even died from handling contaminated air filters. I may can help more if I knew exactly what you wish to filter.
Just for if there are no more And Just air, i think of volcanic ash and very fine dust. Fine dust as that gets more and more,have pre filters and hepa in the bedroom,the pre filters turn brown in 6 months.so i guess i need filtering for ISO ePM2,5 0.3 - 2,5 µm second pre filter and ISO ePM1 0.3 - 1 µm in the bedrooms. I buy them now, but like to know how to improvise .
