Silica dust exposure and respiratory effects in Semnan Ferrosilicon workers

Introduction. T o qualify a nd e valuate work pl a ce ex posur e to ai rborne "f r e e crysta lline silica dust" in the Ferros ilicon manufacturing plant a nd to as sess pulmon ary fun ctions and respirat ory symptoms among worker's in the industry establish ed fo ur years ago.Attempts were made to investigate whether a four yea rs pe riod of exposure to silica dust may alter lung function val ues and res ult in respirato ry symptoms. Materials and Methods. Individu al mon it orin g a nd s iz e -s elect ive g r a vime t r ic sampling procedures were used to estimate worker's expos ure to tot a l and respi rabl e si ze dust levels.Gravimetric a nd x-ray diffr a ction tech niq ues we r e use d to qu an t ify airb o rne d us tco n ce n t r a t io ns a nd free c rys ta ll ine sili ca co n t e n t s of samples res pe cti v el y.subj e ct s wer e in t e rv ie wed by a sta nda r d ized r e spir a t or y questionnaire.Spirometry tests and chest radi ography were taken to eva luate th e effec ts of workpla ce exposure o n worker's he alth . Mean lu ng fun ction va lues a nd re spira tory symptoms inc ide nce s were compare d in studied gro ups by t-test.ch i square and logistic regression ana lyses. Results. T otal gravimetri c du st co nce nt ra tio ns ra nge d fr om 4.1 to 22 rrig/rn ' while respi rable mas s frac tio ns ra nge d fr om 1.5 to 12.5 mg/m3 .Fre e crys ta lline sili ca conce nt r atio ns in colle ct ed d ust samples meas ure d a t le a st 1.2% a nd maximum 6.3% .Th er e were no significant differences in smoki ng habit, age a nd yea rs o f employment between studied subjects.Forced Expira to ry Volume in one second FEV I (P = O. l) a nd the ratio of Forced Expiratory Volume in o ne seco nd to Fo rced Vit a l Capacity (P=O.l) were significantly lower in exposed workers th an unexposed group,but no differen ces were found in other lung function valu es between suhj ects.Work re lated re spiratory sympto ms including pulmonary infilt rati on,spu t um an d co ug hing we re slight ly more prevalent among workers but th e differences were not signi ficant. Conclusion. Current exposure to respirable sili ca du st is high er than th e thres ho ld limit value calcula te d at 1.1 mg/m3 based on American Co nfe re nce of G ov ernmental Ind ustri al Hygienists formula. Free crysta lline silica contents of ai rborne dust sho uld be co nside red as a substa nt ia l ha zardous age nt and may alter lu ng functi on a fte r sho rt period of exposure therefore e ngineering preventive measures are needed to minimize the exposur e,