Answer to Question #1869 Submitted to "Ask the Experts"

Respirators that are correctly fitted and properly worn are designed to protect the worker against hazardous airborne chemicals, toxins, or radioactive materials. The answer to your question on whether respirator protection is needed will depend on the amount of uranium that will be suspended in air during the job, the chemical form and particle size of the uranium dusts, and the duration of the exposure. Respirators should be worn by workers when it is necessary to conduct work in areas where it is likely that the applicable exposure limits will be exceeded. You must determine the applicable standard for your work. Since you do not know in advance the precise airborne uranium concentration prior to starting the job, it would be advisable to make some conservative estimates and then compare your estimates to applicable standards. If your estimates of the airborne uranium concentration exceed those limits, then you should wear suitable respiratory protection.

You did not provide us with the identity of the regulatory authority under which you are doing this work. For example, in the United States exposure limits have been established by the American Conference of Governmental Industrial Hygienists, the U.S. Nuclear Regulatory Commission (NRC), and the U.S. Occupational Health and Safety Administration, among others, for each contaminant of concern. The NRC follows the recommendations of the International Commission on Radiological Protection's (ICRP) annual limits on intake and derived air concentrations (from ICRP Publication 30). The Occupational Safety and Health Administration (OSHA) established long-term and short-term permissible exposure limits to control worker exposures. The U.S. Department of Energy, the American Conference of Governmental Industrial Hygienists, and the American Industrial Hygiene Association have published guidelines and threshold limit values to control uranium exposures. These standards protect against both radiation and chemical-toxicological effects of uranium for both soluble and insoluble chemical forms. For example, the OSHA permissible exposure limit is an eight-hour time-weighted average concentration of 0.05 mg uranium per cubic meter for soluble compounds, and 0.25 mg uranium per cubic meter for insoluble compounds. The NRC annual limits on intake for depleted uranium can be found in Title 10, Code of Federal Regulations, Part 20, sections 1001 to 2401, Appendix B. These limits are given in terms of annual limit on intake for three solubility classes. The NRC has also established a weekly inhalation limit of 10 mg soluble uranium in addition to the annual dose limits [10 CFR 20.1201(e)].

Many assumptions are involved in determining the airborne concentration for uranium and the potential intake by a worker, including the specific activity of the uranium, the ventilation rate, whether the worker is a nose or mouth breather, particle size distribution, and the time spent in the dust environment. Given the thickness of the depleted uranium dust layer, the type of job, and the activity count rate you describe, it appears to this expert from the outset that for a cutting operation, respiratory protection would be necessary.

Darrell R. Fisher, PhD