Release of Aerosols during Sawing and Milling of Beryllium Metal and Beryllium Alloys

Abstract

In spite of stringent standards for occupational exposure of workers to airborne beryllium, new cases of chronic beryllium disease continue to occur. Many of these cases are among workers involved in the machining of beryllium metal. Although the exposure history of most individuals recently diagnosed as having chronic beryllium disease included exposures above the current occupational standard (2 μg/m³), there are limited data on the source of beryllium aerosols and on the inhalation toxicology of beryllium metal. Similar information is lacking on the source terms and toxicology of beryllium metal alloys. Although no cases of chronic beryllium disease have been diagnosed among machinists working exclusively with beryllium alloys, it is not clear whether this results from a lower probability for inhalation exposures above the occupational limits or from an intrinsically lower toxicity of beryllium in dilute alloys. The work reported here was undertaken to better define the potential aerosol source term for occupational exposures to beryllium metal and beryllium alloys during two common operations: sawing and milling. Standard machining methods were used to saw and mill billets of beryllium metal, beryllium–nickel alloy, and beryllium–copper alloy. Particle size distributions and aerosol concentrations were measured to evaluate material typical of that which might be accidently inhaled by workers conducting these operations. All particles were irregular in shape and had projected area diameters extending down to the micrometer range. Concentrations of airborne beryllium in the general workplace remained less than 2 μg/m³ because of engineering controls, but peak concentrations in the ventilation shrouds exceeded 7 mg/m³ during the milling of beryllium metal. The rate of total aerosol production was highest when using beryllium metal and was more than a factor of 10 lower when using nickel and copper alloys. This difference probably resulted from the more brittle nature of beryllium metal and its response to mechanical disruption. Taking into account the mass fraction of beryllium in the alloys (approximately 2%), the airborne beryllium production rate for the alloys was more than a factor of 500 lower than for the metal. These results indicate that the potential for accidental exposure to beryllium from machining of metal is significantly greater than from machining of alloys.