Document XzxNd9oyy4RpXgrQxbG0LZJ7g

*n POSTAL AOMCSS: ox xi. cto*ct snurr nm. p.o. STSNCT mtPHOHI: * ut* * EXTENSIONS *7T. 2Ni atJjH::. NEW SOUTH WALES DEPARTMENT OF PUBLIC HEALTH occupational health DIVISION OF RSnmTW^:KSIEUK 86-88 GEORGE STREET Nth.. STDNEY 11th September, 1962. Sr. I. D. Lethao, Physician, Occupational Healthy Department of Public Healthy Bor 134 3.F.O., PEPTH, 7estem Australia* Sear Dr. Lettac, 2eTerence Your Letter of 14th August, 1962, concerning dust retention by filter pads of respirators. Size analysis of lust particle sizes retained by filter pads of respirators in difficult to achieve accurately. The major drawback is the incomplete removal of dust from the pad, unless the latter can be chemically dissolved, or eliminated in scse ray, leaving the dust in suspension, without affecting it. The type of material in the filter is not mentioned, e.g. whether paper, cotton wood, or resir. wool. The erfici^ncy ci such filters can be aich mors readily obtained by artificial cams, such as dust testing on each side of pads through which dust laden air is drawn, or o.v the methylene blue penetration test, which includes particles icru to 0.1 micron. High efficiency pads retain in excess of $9 per cent of the methylene blue. *. number of methods be used to get cut a great deal of the duct from a pad, .eaher of alcohol-water mixture or the ure of sound x-avpe ;'*t oil dust is removed in this way, which couid ic'id '.jt. vV :;.i efficiency ~i *ho rvi. `t'li :>y iU: .*1, dust, :*)r free r.ilica .c ar.--.*ysm-y erne asc, .eve. *i in.;.-. * 5 r.r f#s <o*n 11 01Tai AOOttii. OX 1 a. GtOICl STHtiT Nik. f.O -VSNT TSL**ON|- U 42<t ... tos* ixrtHUam m. .'* NEW SOUTH WALES DEPARTMENT OF PU8UC HEALTH OCCUPATXOHAL health division of JtaanrajatLWojQHK 86-M GEORGE STREET Nth.. SYDNEY 11th September, 1562. C 4195 It. I. D. Lethaa, Physician, Occupational Health* Department of Public Health* Box 124 O.P.O., F33TK, .Veatem Australia. Dear Dr. lethac:. Reference Your Letter of 14th August, 1562, concerning dust retention by filter pads of respirators. Size analy3i3 of lust particle 3izes retained by filter pads of respirators io difficult to achieve accurately. The major drawback is the incomplete removal of lust from the pad, unless the latter can be ccenicaliy dissolved, >r eliminated in sera -ray, leaving the dust in suspension, without affect in? it. The type of material in the filter is not mentioned, e. g. whether paper, :o;tcn rood, or resin wool. The erficiency of such filters can be aich core readily obtained by artificial ieirs, such a? lust testing on each side of pads through which dust laden air i; drawn, or o.v the methylene blue penetration test, which includes particles ir-:: to D,1 micron. High efficiency pads retain ir. excess of 59 ?or cent tie cettylsrn? blue. :.'.L*.ter of neticds cbe used to get cut a rreat deal of the duct from a pad, -uor : toar-ir.:.; ir. a :fterror of alcohol-water mixture >? t .a --.-re of sound r-v/*e free * ilica