Fiberglass insulation inside ventilation systems should be sealed or, better yet, replaced with non-fiberglass insulation. Fiberglass insulation in attics and walls should be covered in paper, foil, or (preferably) plastic. Pressure relationships should be maintained so air goes into the wall or attic, not out of it into occupied spaces.  If fiberglass or fiberglass-bearing dust has to be disturbed in a remodel, it should be moistened to decrease the dust, and the area isolated (see section 7.5).  If an area is heavily contaminated with fiberglass dust it may have to be vacuumed using HEPA-filtered vacuum cleaners to cure the problem.

If there are epidemics of eye irritation, fiberglass is one of the first suspects. If you can look up at a supply vent and see pieces of fiberglass caught in the vent, there is a problem. Also, if people come into an office in the morning and find debris in areas below vents, this is usually fiberglass.

As noted above, fiberglass is commonly found in buildings as insulation. Large quantities can be released into the air during remodels. Ceiling tiles usually contain fiberglass, and high levels can be released, for example, if an earthquake knocks tiles down. Fiberglass particles can also filter down from above ceilings. But probably the largest source of fiberglass contamination in buildings is the ventilation systems. Nearly all ventilation systems have fiberglass exposed to the air stream. It eventually breaks down and blows out.

Fiberglass is medically recognized as an irritant to skin, eyes, and upper respiratory systems. Rashes, sinus headaches, coughing, and conjunctivitis (pink eye) are common effects of exposure to large quantities.

This is still an open question. The U.S. and German governments have it classed as a possible carcinogen. While more research is needed, it is certainly not in the same class as asbestos. It seems likely that workers in plants manufacturing fiberglass may suffer slightly elevated cancer levels.

Fiberglass is simply strands of glass. The form of it known as glass wool, which is made of fine (small diameter) strands, is used as an insulating material and is the most commonly used insulating material in buildings -- found in walls, ceilings, and ventilation systems. It is a part of a larger class of materials called man-made mineral fibers (MMMF) which include rock wool and slag wool, made from fine strands of molten rock and slag, respectively.