I assume you have yards of carpet and some computers around. If you can, I would hot water/steam clean the carpet (and anything fabric that you can do it to) and then go double duty on the vacuuming. If that's too awkward/expensive, you might consider vacuuming it well, then putting down a carpet treatment of some sort, depending on how close the employees are and how easy it is to move them out for a few minutes. One treatment that has been mentioned here is a light misting of a d-limonene (citrus oil extract) solution on the carpet. That should work fast, but don't drench the carpet. To be safe, you probably should move the employees out of the area while and immediately after you do it, and be aware of anyone with asthma. The stuff ordinarily isn't dangerous, but who knows who might be extra sensitive or how aggressive your maintenance people might be in applying it? Avoid spraying it on acrylic surfaces like plexiglass panes.
Another that I've seen good reviews of elsewhere was/is a diatomaceous earth/borate/d-limonene powder product called "DeLime'Inator" by Hansen's Pets. I haven't seen it around lately, so I can't say for sure that it's still available, but it's worth looking for. The d-limonene and DE kills the adults, the borate kills the larvae. Because of the DE, it is abrasive, so if you use it, be careful around the computers. The borate/boric acid-only products seem to work pretty well, but they will take a bit of time -- they kill larvae fairly fast, but seem to take from a few to maybe 14 days to kill adults. The powder carpet treatments generally will last until you clean the carpets with a liquid medium. You also might try thorough vacuuming maybe 1-3 times a day for awhile and see if that helps. When you finish vacuuming, vaccum up a little corn starch to suffocate the adults that the vacuum picks up (or empty the bag). A company that does flea treatments for floors and other areas is Fleabusters (www.fleabuster.com
), but I don't have personal experience with them. They also sell the dry carpet product, Rx For Fleas, (presumably a borate product?) that they apply.
If, on the other hand, you have hard surfaced floor instead of carpetiing, then a spray down with a mild d-limonene solution should go a long way to solve the problem (spot test it to be sure it doesn't affect the finish). Even a soapy water spray should get many of the adults.
There are some other flea threads on the forum that you might check, but most of them involve animals, which I assume you don't have. If animals are involved in the office, that's an added dimension. The fleas came from somewhere, but you probably have sidewalks into/out of the building. Unless your employees track around on the grass before coming into the office, I doubt the immediate outdoors is the source. If it is, apply beneficial nematodes to the grounds to control the larvae. There are other strategies that perhaps others will post, but those are a few ideas.