Officials in Binghamton, N.Y., are grappling with a unique health problem: an 18-storry office building completely coated -- floors, ceilings, walls, even inside desks and office machines -- with a fine ash that contains large proportions of the hazardous chemical PCB.

"It may be the first time a modern office building has ever had to be cleaned of toxic chemicals -- and that means scrubbed from top to bottom.By hand," said Dr. Arnold Schechter, health commissioner in Broome County, N.Y. "And we aren't sure at what stage of scrubbing we can call it clean."

Rugs and sofas in the building are being discarded, and Schechter said, "IBM is about to learn whether you can clean a typewriter inside and out of a layer of toxic chemicals. We also had copying machines and computer terminals that we are not sure what to do with."

A small fire and explosion in the basement of the Binghamton building a few weeks ago caused an electrical transformerr there to burst. The transformer contained about 180 gallons of insulating and cooling fluid, two-thirds of which were polychlorinated biphenyls, or PCBs.

Fortunately, the fire occurred at 5:30 a.m., when the building, which houses offices of the state's Department of Environmental Conservation, was unoccupied.

Building operators around the country are watching the situation closely because, according to a General Electric spokesman, indoor transformerrs loaded with PCBs are "the rule rather than the exception" in office buildings in America. Because of PCBs for many years were thought to be harmless chemicals that were very good at preventing electrical fires, they were the chemicals of choice for electrical equipment that was to be installed indoors. Cheaper materials are used in outdoor transformers.

A crew is now going over the building and all its contents with a fine-filter vacuum. After that the building will be scrubbed with soap and water.

The workers cleaning the building are specialists who work in protective suits and special breathing masks.

But questions remain. "What do we do with insulation in the ceilings?" Schechter asked. "And what about the ceiling tiles -- will they pick up too much to be cleaned?"

Since this is the first accident of its kind anywhere, health officials not only don't know how much cleaning is enough, they don't even know how, where, and what to clean. They are now poring over hundreds of papers on PCBs and the otherr toxic chemicals that are associated with them, in order to get some idea of what levels of the substances "would be safe enough so a pregnant woman could work in the building without fear," Schechter said.

The fire and the explosion released the PCBs into the building's basement, and the ventilating system sucked up the smoke and ash and blew it into every office and corridor.

When Schechter had some of the ash analyzed, he found that it contained between 6 and 20 percent PCB. "No one has ever had a situation quite like this before, so we are on our own. We have to figure out how clean is clean, and when we can certify the building okay for use again. It could be six months, a year, five years -- we just don't know." The cost of the cleanup will be several million dollars, at least.

Peter gillson, the General Services Administration's PCB coordinator for the 250 or so federal buildings in Washington, said that "fire damper"" circuits and vent systems will be installed in federal buildings to help prevent the sort of accident that occured in Binghamton. When a fire starts, these circuits melt and shut down the vent system.

PCBs, which are not found in nature, were first marketed in the 1930s. They are heavy oils that are chemically inert and will not break down and so continue to be spread around through the environment in tiny amounts. They are also resistant to heat, do not conduct electricity, and will not burn at least that 2,000 degrees.

Because they are so stable, they remain in the environment and have turned up in soils, animals, fish, even human mothers' milk. Their manufacture has been banned since 1979, but since electric transformers last 20 or 30 years, most office buildings in America still contain PCBs.

In humans, large doses have been found to cause acne, liver damage and other body changes, while in animals they cause cancer. It is too early to tell if they cause cancer directly in humans, but, according to Dr. Irving Selikoff, an expert on the medical effects of PCBs, there is some evidence that suggest they may induce other chemicals to become carcinogens.