Our Atomic Energy Program is one of the truly enormous enterprises of our national life, ranging from mining to computers and heavy industry to oceanography. Consequently, the total number and variety of industrial hazards is potentially large but, fortunately, most of them fall into the category of accepted industrial hazards and require no particular comment. However, when radiation and radioactivity become components of the overall process, each situation and operation must be individually re-evaluated and new industrial standards established as needed. This, of course, is standard procedure at all atomic energy projects, and as a result the AEC has been a partner to a remarkable advance in industrial hygiene and safety engineering techniques. Emphasis has been, and is, on the anticipation of hazards, followed by strict application of preventive measures and education of the worker. In many instances the design and operation of a plant or process has hinged on the recommendation of the health-safety groups. A very welcome by-product of this concern is the enviable industrial record of the AEC contractors.1 The lung features very prominently in all thinking and planning concerning possible exposure of personnel to both radioactive and non-radioactive agents. It is recognized as one of the more effective routes for introducing substances inside the body, considering that the alveolar ventilation in an average man amounts to nine kilograms or more of air per day. Whether foreign material in the inspired air will eventually reach the systemic blood depends on its particle size, solubility and some five additional minor properties.2 In general, by the time the air reaches the larynx, particles larger than about five microns have been removed by the straining action of the vibrissae and by impaction on the moist mucous membranes of the upper respiratory tract; and similarly when the air reaches toward the finer bronchioles, the majority of the particles are one micron in diameter or less; the finest particles have been shown to reach the alveoli. If the larger particles are insoluble, they are removed mechanically by ciliary action and coughing. Particles brought up from the tracheobronchial system are for the most part swallowed; if they remain insoluble in the presence of the digestive fluids, their effect is negligible, but if they become soluble or chelated, they may be absorbed into the systemic circulation.3