As if the air outdoors weren't bad enough, a new report suggests poorly cleaned central air conditioners pose a serious health risk to millions of office workers in Shanghai.

According to a recent report by the Shanghai Indoor Environment Purifier Association (SIEPA), about 95 percent of the city's office buildings do not regularly clean their central air conditioning systems, and less than 5 percent of the 4,000 high-rise properties in Shanghai reported that they cleaned their ventilation systems on an annual basis.

Neglecting ventilation facilities results in serious indoor air pollution, and can cause considerable harm to a worker's health.

Industry experts said the aerators installed in office buildings could provide ready shelter to various kinds of mildew, acarids and bacteria if they are not cleaned frequently. Dirty central air conditioners could become serious transmitters of viruses, pollutants and infectious diseases like influenza.

"More attention should be paid to indoor environmental sanitation, especially since most office workers usually have to spend at least eight hours a day in the office," said Wang Fang, the association's secretary-general. "The vent pipes of these central air-conditioners should be cleaned at least once every two years, while other equipment, like condensers and water tanks, should be cleared out twice a year."

In addition, the central air-conditioning systems in office buildings should be equipped with proper air purifiers, Wang said.

Michelle Liu, a local white-collar worker, said she had noticed a "weird odor in the air" ever since she started working at a 30-storey office building on Central Huaihai Road last year.

"The smell gets worse when offices on other floors are under renovation. My office is filled with the odor of oil and fresh paint," she said. "I believe the odor is harmful and ruining my health."

The report said the high cost of cleaning a central air conditioning system made many property management companies reluctant to maintain their systems.

Wang said it can cost 200,000-500,000 yuan (US$25,880-64,700) to clean the central air-conditioner system of a medium-sized office building.

Some property management firms even said they did not know how often an air conditioner should be cleaned.

(China Daily April 10, 2007)