Tennis balls are produced and manufactured with
natural rubber latex bladders which become abraded
when used as floor protection on chair legs. Using tennis
balls for this reason can produce latex dust in schools’
indoor air. Some students and individuals are highly allergic
to latex.

The EPA (Environmental Protection Agency) has reported that indoor
air contains 2-5 times more pollutants than outdoor air.

The Massachusetts Department of Public Health labels tennis balls as a
source of indoor air pollutants in their August 2006 report “Indoor Air Quality
Testing - Pediatric Asthma Surveillance in Massachusetts Public Schools”.

Tennis balls have a hollow core and some varieties of tennis balls are filled with
nitrogen gas in the center. Nitrogen gas will be released when punctured to allow                                              the tennis ball to be retrofitted to school chair legs exposing maintenance personnel                                           to this gas.

The American Lung Association has recently made statements that they  are concerned about indoor air quality.

This is from a report on indoor air quality from the State of Massachusetts –

Department of Public Health,  Bureau of Environmental Assessment.