Document rpnkKD89B66O1r3Jqabr63eqV

Qinns^ *" ,, ;,v jtnn. oeaip. Hyg. Vol, 16, pp, 417-419. Pergamon Press 1973. Printed in Great Britain '* ` '' '&*. , 1 -j` ,v \-. \j,> '^\;Vrt *>y5i, 'y` 0<*/kw''Y VS > after intratracheal ad- ,.;K-;y,V>fvi. le represents a dose of - v " y 'lo previous doses.) *'' ; ' ( - I" , \`r. HI (Edited by Walton, ; n, W. H.) Vol. 1, p. 157. ttel-Forsch. 21, 142. i , (1971) lnt. J. appl. Rad. . A. W. (1972) Am. Rev. /. Physiol. 33,757. r.-:h ., :* \sj:- /i/V; R` .: HM Factory Inspectorate, ` ^W *;v< ' / - 'V..' ; ' '-''''ffyry yi's>;i:.;:.V.;yi. ^ yv:^' Trichloroethylene is widely used in industry as a vapour degreasing agent add, ' , ' -f at the present time, there are about ten thousand degreasing units' in Britain based on y ;; this solvent. The toxic properties of . trichloroethylene are-well known and its Threshold Limit Value is 100ppm.,Specialgrades of trichloroethylene can alsp be y ;. . `)yV .used in the metal finishing industries as a drying agent andThis.process is similar 7": 7, ,'yyy to vapour degreasing. Morerecently another chlorinated solvent,; !,1,1-trichkmy ? : i '7 ethane, has been introduced as a vapour degreasing agent.' Tlijs has long been known y ' ^ f| as a cold cleaning solvent but new stabiliser systems have been developed to permit its use in vapour degreasing. lt has the advantage that it is somewhat less toxic than trichloroethylene with a Threshold Limit V^lue pf 35g '< -r In a recent survey, atmosphere sampling w^s Carrie^ ; degreasing plant in twenty-one factories in the Sopth Md-l^dlands pIF^n^lad^'j';^'''7 . v-y Workers wore personal samplers to measure their average exposure over most of a ' ' working day and other atmospheric samples were taken at selected points around the y degreasing tanks.' ;L-'"' ;jy' 7y Familiar problems were found at a dumber of tanks and, of, the seventy-one , workers who wore personal samplers, one quarter were receiving an average conceri-! ? ;: )/ - . ?`y tration of trichloroethylene in excess of the threshold limit value throughout their working day. Modern industry operates at an ever-increasing pace and many tanks are used to-the limit of their capacity. The result is that short cuts may be taken and excessiv^iuantities of trichloroethylene can enter the workroom air. Similar problems can exist with 1,1,1-tricbloroethane but, during the survey, concentrations of this solvent in air were well below toxic levels, during tfo^nm vapour degreasing.. ; , y The results of the survey ca^lhe^ipjn^ed under twp headings, "Ventilation"; ' and ``Method of operaji/ ' ' i-- ; ,;7V. * IL'ATION Lip exhaust ventilation was provided at three-quarters of the open-topped tanks of the survey. Standards varied widely and the ,etiractfen rates at tanks from velometer measurements varied from,0 to/>100 ft3/mm per square foot tank surface. At tanks at which operators'were receiving average, concentrations above,* the threshold limit value,Uhe highest lip extraction rate was only 21 ft3/min per square foot. It was quite common to find the lip slots partially or even completely closed 417 7 ' SL 036775 .418. R. W.Kay ITM where heavy objects had been dropped on the edge of tanks and in some cases the lips ` poorer at tanks without lip exhaust and over above the threshold limit value tank without lip extraction requires ^very'deliberate procedures in a very well ventilated area and these conditions were not: : most of the tanks. At semi-automaticunits, a good standard of local exhaust ventilation was required where operators loaded and unloaded the units. / . " While exposure to solvent vapour is mainiy a problem in the immediate area of 111 thej.tank, poor conditions at some tanks,were aggravated by a poor standard of 1 general- ventilation. Good general ventilation is always essential where a tank is : J: v || situated in a small room. In some factories, draughts had a beneficial effect on the concentration of solvent vapour in air but, in other cases, downward draughts caused solvent vapour to be blown out of the tank and into the operator's breathing zone. The effects of draughts could be limited by the use of covers and screens at the tank. , ,, - '* -'"y'iiv.'f.j METHOD OF OPERATION la TThhee hhiigghheesstt concentrations of solvent vapour in air usually occurred during i` unloading if an insufficient time had been allowed in the freeboard zone of the tank. | Many operators whose iong term samplers showed concentrations well below the / threshold limit value were exposed to very unpleasant conditions during the short \ periods in which work was removed from the tank. Mechanical handling has the advantage that work can be ^suspended in the tank without any effort from the operator and he is not required to bendover the tank to load or unload work. ' * : lh many factories problems were caused by the way work was prepared before 1;; ;.,,0 . its insertion in the tank. Baskets, jigs and other workpieces were often too large to fit into The freeboardzoneand few, operators removed this work in stages from the pSv1 tanks. During the degreasing of hollow articles, great care was taken in some factories . to stack the articles in such a way that liquid trichloroethylene could drain easily but, in other factories,; hollow articles were stacked at fandom with the result that hot solvent was always removed into the workroom air. Standards of maintenance were / v ,v. low at some tanks and this was reflected in an insufficient supply of water to the cooling I fir' ^ co^s> gaskets arid damaged and inefficient extraction systems. Y ; 1. Degreasing tanks should be sited in well ventilated areas and particular ,7//V" attention should be given to general ventilation where a tank is placed in a confined work area. The effects of draughts can be minimised by the use of covers on the tank and the provision of draught screens. 2. Vapour degreasing tanks in regular use should be provided with an efficient . lip exhaust systeiri. An extraction rate of about 35 ft3/min per square foot tank surface was fourid to give an adequate standard of protection. Where tanks are used at widely spaced intervals, lip extraction is still required if the operator is exposed to Concentrations well in excess of the threshold limit value during work at the tank. Very small degreasing tanks may not require lip extraction but, in the survey, the 11 f SL 036776 Toxic need for lip vehtilatii two feet by two feet. 3. Work should t the tank during the n 4. Work should b solvent can take plac 5. Operators sho solvent in the freebo; mechanical handling few feet from the tar can be assisted if woi hooks. 6. Degreasing ta particularly necessar; 7. When tanks Section 30 of the Fac 8. Operations v carried out in areas be decomposed to p ditions. \ ji some cases the lips ^exhaust and over ireshold limit value p extraction requires, conditions were not lard of local exhaust he units. . ^ . e immediate area of i-'y a poor standard of :ial where a tank is neficial effect on the /ard draughts caused or's breathing zone, creens at the tank,' : illy occurred; during ird zone oftli^ tank, cions well below the jns during the short :al handling has the any effort from the unload work, was prepared before often too large to fit ^ciinn stages from the m in some factories Id drain easily but, h the result that hot of maintenance were f water to the cooling ems. solvents can be conrved: areas and particular placed in a confined of covers on the tank ided with an efficient per square foot tank Where tanks are used : operator is exposed ing work at the tank, lit, in the survey, the Toxic hazards with trichloroethylene and 1,1,1-trichloroethane 419 need for lip ventilation was apparent in small tanks with surface measurements of- two feet by two feet. -r:,yy[. 3. Work should be arranged so that it can be contained in the freeboard zone of the tank during the removal of excess degreasing solvent. . ,; 4. Work should be stacked so that rapid and complete drainage of the degreasing solvent can take place. 1 - " 5. Operators should aliow sufficient' time' for the rempval of excess degreasing solvent in the freeboard zone. Degreasing operations are much easier to control l)y mechanical handling and this system has) the advantage that the operator is kept a few feet from the tank. With manual operations, the,removal of liquid and vapour can be assisted if work is placed on shelves in the freeboard zone or suspended from 1hooks. niVrWi 6. Degreasing tanks .should be regularly maintained, t Regular maintenance is particularly necessary for the condenser and extraction systems. 7. When tanks are entered for cleaning or maintenance, the requirements" of Section 30 of the Factories Act, 1961 shouldbemet. ^ 8. Operations which require high temperatures, e.g. welding, should not be carried out in areas where solvent vapour may be present.; Degreasing solvents can be decomposed to phosgene and other toxic breakdown products under these con ditions. / 7 7",.v?. , `>.77 ^ >' SL 036777