The harmful effects of asbestos dust on human bodies have long been discussed, and current environmental issues have resulted in the recommendation of stricter standards for-regulating airborne asbestos dust in several countries. In the case of applying the asbestos heat exchangers to certain equipment, especially to home appliances, the level of asbestos dust emitted from these appliances should be carefully taken into account because of the need for airseals which rub against the moving .surfaces of the heat exchangers.

Generally, these heat exchangers are operated throughout the year for a long time. Therefore, it is very important to determine the transition of asbestos dust emissivity with the lapse of time. Besides, in order to prevent the heat exchangers from dispersing asbestos dust1 it is indispensable to clarify the factors affecting the emission. Some experiments were carried out along these lines.

Reported in this paper are the results of an asbestos dust emission test from a test unit which was so designed that typical emission levels for appliances with asbestos heat exchangers of regular specifications would be attained. A prototype for a home-use ventilator incorporating the heat exchanger is also described here.