from the side walls 13 and 15 the air circulation unit is powerful enough to create a plurality of air changes per hour so as to create an envelope of superior quality air surrounding the person working in the work space fig3 is an enlarged fragmentary plan view of the device shown in fig2 showing the unit in greater detail with portions broken away and in section the relationship between the unit lid 19 and side walls 13 and 15 can be seen air exits beneath the unit lid 19 as shown by the arrows indicating flow of air air which is driven by motor blower 25 shown in fig4 exits the blower exhaust cap 27 into the area beneath unit lid 19 thereafter flowing out over the person using the work space located in the unit 17 is blower motor 25 positioned on the top half of platform divider 29 filter 31 in this case a hepa filter is located below platform divider 29 platform divider 29 divides unit 17 into a lower intake chamber and an upper air discharge chamber air enters through air inlet 23 and passes through hepa filter 31 since platform 29 does not permit flow of air through it except through the filter 31 filter 31 is held in place by a filter attachment wing nut assembly 33 filter 31 comprises an air filter which is known generally as a hepa filter hepa filters are commercially available and have an efficiency rating of at least 99 97 at 0 3 microns using a dop test procedure inside filter 31 a pre filter such as activated charcoal may be used to trap odor the pre filter may also include a polyester or other synthetic filter.