Surface area of respirable beryllium metal, oxide, and copper alloy aerosols and implications for assessment of exposure risk of chronic beryllium disease

The continued occurrence of chronic beryllium disease (CBD) suggests the current occupational exposure limit of 2 mg beryllium per cubic meter of air does not adequately protect workers. This study examined the morphology and measured the particle surface area of aerodynamically size-separated powders and process-sampled particles of beryllium metal, beryllium oxide, and copper-beryllium alloy. The beryllium metal powder consisted of compact particles, whereas the beryllium oxide powder and particles were clusters of smaller primary particles. Specific surface area (SSA) results for all samples (N530) varied by a factor of 37, from 0.56 6 0.07 m2/g (for the 0.4–0.7 mm size fraction of the process-sampled reduction furnace particles) to 20.8 6 0.4 m2/g (for the #0.4 mm size fraction of the metal powder). Large relative differences in SSA were observed as a function of particle size for the powder of beryllium metal, from 4.0 6 0.01 m2/g (for the particle size fraction .6 mm) to 20.8 6 0.44 m2/g (for the particle size fraction #0.4 mm). In contrast, little relative difference in SSA (,25%) was observed as a function of particle size for the beryllium oxide powder and particles collected from the screening operation. The SSA of beryllium metal powder decreases with increasing particle size, as expected for compact particles, and the SSA of the beryllium oxide powders and particles remains constant as a function of particle size, which might be expected for clustered particles. These associations illustrate how process-related factors can influence the morphology and SSA of beryllium materials. To avoid errors in predicting bioavailability of beryllium and the associated risks for CBD, the mechanisms of particle formation should be understood and the SSA of beryllium particles should be measured directly.