report; the maximum permissible lung burden maximum permissible concentration in air (MPLB) (MPC,). and the The MPLB is the total amount of a given radionuclide in the lung of an average size man that will result in the lung being irradiated at the maximum permissible lung dose (MPLD). The MPC, is the concentration in air that will result in an average adult male obtaining. a MPLB and hence a MPLD by breathing the air. It is important to recognize that the MPLD is the primary standard; it applies to all radionuclides and radiation sources. The MPLB and the MPCa are derived standards and are specific for a radionuclide. are related These derived standards to the biological properties of a radionuclide and to the form of raciation it emits. Table I lists the existing exposure standards for employees of the nuclear industry that apply to Pu-239 in insoluble form. The MPLD of 15 rem/yr is included in the recommendations of the Internaticnal Commission on Réciological Protection (rerp) ® the National Council on Radiation Protection and Measurements 8/ (NCRP)?, and ICRP Publication 9, the Federal Recommendations of the International Commission on Radiological Protection Pergamon Press, Radiation Council New York, 1966, p. 14. (Adopted September 17, 9/ NCRP Report No. 39, Basic Radiation Protection Criteria, NCRP Publications, Washington, D. C.; Jan. 15, 1971, p. 106. 1966),