Document qmRqdYY9DQmeNganzjGodQd0K

-56- oomes in metal drums or 100-pound paper lined 'bags. About 370C pounds of powdered graphite is used per batch and one batch is made per day on an average. The graphite is dumped into the mixing kettle by men with an average service of seven years. This operation requires about forty minutes per batch per man on an average. Three men are usually engaged in this dumping. They wear respirators while hand ling and dumping graphite, which is not a particularly dusty operation. The average dust produced is 1,803,080 particles, ten microns or less, per cubic foot of air. AH of these dust particles are rounded or slightly angular, black opaque; amorphous, 60oty or dark grey in appearance under the Konimeter microscope, and three microns or'less in size. . J. - SLATE FLOUR; Slate flour (300 mesh) gives rigidity to asphalt on "fast sur faces" such as steep roofs and pipe lines, and prevents its running off. It also produces desirable weathering properties. Mixtures as low as 10# slate flour and as high as 40# are used. An average of two tons of slate flour is used to each still which averages about 800 barrels of steam reduced asphalt. Since the slate flour is introduced by the use of closed pipe lines and centrifugal pumps, the only dust produced is that which results during the unloading of the sacks and dumping them into the hopper. The slate flour comes in 50-pound paper bags, 750 bags to a railroad box car. Four men with an average service of about a year, open the bags and dump the slate flour directly into a hopper from which it is siphoned by campressed air to a storage tank holding about 15 tons. About four carloads a month are received and an average of about 5-l/2 hours is required to unload each car. About one and three-quarter million pounds were dumped during the last quarter period. The men wear MSA Ccaafo respirators. A soreen analysis of this slate flour showed that 99,7% passed through a 200 mesh screen and 96. B% through a 325 mesh screen. Due to the fineness of slate flour and its low bulk density (1.04) con siderable dust, an average of 12,007,680 partioles, ten microns or less in site, per cubic foot of air, end counts as high as 16,538,880 particles per cubic foot, are produced during dumping the sacks and filling the storage tank. About 99% of these dust partioles are slightly angular, transparent, crystalline in appearance under the Konimeter miorosoope, and five microns or less in size; 2% are semi-opaque, slightly angular. There were a few plate like particles which appeared to contain small air bubbles, and a large number of small black particles. A petrographic examination made of a slate flour sample at the United States Bureau cf Mines Experiment Station in Pittsburgh, Pennsylvania showed that it con tained more than 1% Quartz (Si02), 30# Sericite (K2O-3AI2O3-6 SiOg-s^O), 4:0# opaque and 3C# five different unidentified constituents. A chemical analysis of slate granules and flour (Jour. Indust.Hyg.Vol. XV. ,No. 2,Mar. 1933,p. 67) reports these constituents: Silicon Dioxide ...... Titanium Dioxide............ Aluminum Oxide................ .. 18. 81# Ferric Oxide.................... Ferrous Oxide ................ .. 6.58# Managanous Oxide............ Calcium Oxide................. .. 0.42# Barium Oxide..................... * 0# 05% Magnesium Oxide... ......... 2.21# Potassium Oxide... Snd1um Oxide. ..... ......... 1.88# Water below 110C. 0#32% " above " . Phosphoric Oxide.. Carbon Dioxide.... Ferric Sulphide... Specifio Gravity - 2. 795 "The silicon found, though expressed in the chemical analysis as silicon dioxide, is not differentiated chemically as to the forms present in the original minerals, whether free silica or silicate." EM001546