Static electrification of airborne asbestos: a study of its causes, assessment and effects on deposition in the lungs of rats

The paper describes a series of experiments carried out in the laboratory to investigate how asbestos fibres might become electrostatically charged during the process of being made airborne, the magnitude and polarity of the charge per fibre, and the effect on lung deposition in rats. Measurements of the penetration of fibres through an electrostatic elutriator enabled the magnitude and distribution of charge in a cloud of fibres to be quantitatively assessed. Thus it was found that a typical fibre of UICC amosite, as dispersed in a typical animal exposure chamber, carried a net charge of magnitude equivalent to about 60 electrons. The distribution of charge was bimodal, suggesting that two charging mechanisms were taking place, the main one producing net negative charge and the lesser one producing net positive charge. These were attributed to materials in the dust dispenser used and with which the fibres came into contact during dispersal. It was found that the magnitude of charge on a typical fibre could be significantly reduced by the introduction of equal numbers of positive and negative gaseous ions from an a.c. corona discharge ioniser. Finally it was found that enhancement by up to 40% of the dust deposited into the slowest clearing part of the respiratory tract of experimental rats was brought about by the electrostatic charge on the airborne fibres. The implications of this finding in the field of occupational hygiene are briefly discussed.