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LABORATORY OF APPLIED PHYSIOLOGY COLLEGE OF MEDICINE GENERAL HOSPITAL July 15, 194-0 Hr. 0. B. Lewis 2thyl Gasoline Corporation Chrysler Building Lew York, Lew York Dear Oscari Thank you for your letter of July 3, with abstracts of the tank cleaning report by Hr. Harrison. These appear to be very v;ell done and after we have had opportunity to go over them in light of the uses to which they are to be put, we will discuss them with you. Concerning your comments on the organic lead in tanks, the figure of 0.04-2$ does represent the mean value and it is true that as this figure is expressed in terms of per cent, organic lead in sludge, it will be influenced in amount or the propor tion of iron, sand and other physiologically inert material present in the sludge, accordingly, as we encounter more and more inert material, the percentage of lead is decreased, but the total amount remains the same, and one might assume from that that the hazard is the same. It is conceivable that in certain situations conditions might occur where the only deposit in the form of sludge would bo lead salts and perhaps a small amount of iron rust and conversely, situations in which the same amount of lead salts are deposited, but due to the contamination of river mud, sand and the like, they would come to constitute but a very small proportion of the sludge. These would represent the extremes, but it is probable that our results are influenced to e degree by this very factor which we seek to eliminate by the study of a large number of samples. But from a practical point of view especially in consideration of the over-all general uniformity in refining and storage practices, that variability within the wide limits encountered in the organio lead content of sludges, does come about as a consequence of differences in the amounts of lead contributed to the sludge rather than the. extremely wide fluctuations in the amount of inert material. One might assume that regardless of the percentage of organic lead the same order of hazard would exist provided of course a sufficient total amount of organic lead were present to saturate the air in the tank with vapor and It is true that regardless of the amount of organic lead in sludge, amounts of lead are found in the air above it. Our recent 1'r. 0. 3. Lewis - (2) - July 15, 194-0 experiments however, indicate that the amounts of lead in the air above sludges that contain organic lead are in general directly proportionate to the percentage of organic lead in the 3ludge. be have not included these experiments in our report but will discuss them later* It follows therefore, that the concentration of organic lead la an important factor, whether we express it in terms of per cent, of"sludge or in amounts per square foot of sludge in tank bottoms. I can not agree with your comments on the validity of the figure 0.042 being influenced by any factors. The figure 0.042;i is a statistical constant, the validity of which can be estimated by Its relation to its probable error which is given. Inapeotion indicates this constant to be 20 times its nrobable error, establishing its validity. Any inferences from this constant would of course be subject to examination. Conse quently, if we wish to use this constant to estimate the probable average organic lead content of the sludge of tanks it would have to be used in conjunction with our data on thickness of sludge. This data is given in Table 12 of the report. These figures are not In agreement with your surmise that many tanks show little sludge, as over 75> have more than 1/2 inch, which would make 72 cubio inches of sludge for every square foot of tank bottom. Moreover, we have no data to support the statement that some tanks 3how no sludge. Fiftyfive of 656 had less than 1/4 inch, but in going over our records, we could find no statement of any tank that contained no sludge.- making allowance for the fact that the figures for the thickness of sludge represent only a rough estimate on the part of the safety engineers, one can easily see that in most tanka there is an adequate amount of lead to contaminate the atmosphere to a dangerous concentration. The extent to which this occurs will be Influenced by a number of factors, suoh as the ventilation of the tank, the ratio between bottom surface and volume and other factors. This is one phase of the problem that we will investigate in our proposed experimental program. 1 In your hypothetical case of a 5000-bairrel tank were the worst possible conditions to obtain, that i3, all of the lead volatilized, and there be no ventilation, it would be possible for a man to become intoxicated in one day*3 work. In so far as the inorganic lead content of refinery tanks is concerned, this would be dangerous only if inhaled aa dust or if swallowed. There is little danger therefore, if tanks KE 0022370 :.r. 0.:B. Lewis - (}) - July 15, V)kG are cleaned while wet and in any event the practical danger of poisoning from this source would he very such less then that from organic lead in the sludge. Legislation and plant practice have demonstrated that amounts of inorganic lead in excess of 1-1/2 to 2 mg. per 10 cu. m. of air will produce intoxication in workmen who are exposed daily. As tank deposits are not 100/ lead, fairly large amounts of dust would have to he present in air to create exposure conditions of significance in so far as the inorganic lead is concerned, particularly 3ince few men work at tank cleaning daily, the operation usually being of an intermittent character* `0 are happy that you asked these questions. These are the type of specific inquiries that I hoped -would arise out of study of the report. Little attempt was made to draw any except general inferences in the preparation of the report, which was a picture of the situation as we found it and it is only when the report has been disseminated and many more questions are raised about it, that it will have its full application to the practical problem. Cordially, vr Dillard L&chle, A:. D. KE" 0022371