Checking HEPA filters?

[Joe Harrington]

I'm looking into the possibility of purchasing a used clean station
that was used in the medical industry. The unit is 6 ft wide, a 
stainless steel cabinet with a formica work surface, and a variable 
speed blower motor.

I've not seen the unit yet, but I do have a picture of it. It apparently
has a six filter array of of 24 x12" filters or perhaps (3) 24 x24 "
filters. The pre-filter is below the work table, so I assume it is 
bottom feed.

I hope to check it out this weekend and the present owner, who is 
not at all familiar with it, had it advertised for $475 or BO.

Would anyone have any suggestions for determining the condition of 
the HEPA filters?  A laser particle counter would be the way to 
properly check this out, but I don't have an extra $2,000 to purchase
one at this time,  :-)

Any suggestions would be much appreciated.

Joe

Mainely Mushrooms