| dc.description.abstract | Background: During additive manufacturing (AM) of sand casting moulds, potential dust species of unknown particle size or mineral composition, and hazardous chemical substances (HCS’s) such as silica (crystalline), volatile organic compounds (VOC’s) and polycyclic aromatic hydrocarbons (PAH’s) are liberated/released during the pre-processing, processing and post-processing phases of manufacture. Aims and Objectives: Bulk sand samples were collected from two research facilities (Facility A and Facility B) in South Africa to determine particle size fractions and mineral composition. Respiratory exposure monitoring of HCS’s was conducted. Methods: Physicochemical characterisation of new, used and mixed bulk sand samples through particle size distribution (PSD) analysis, scanning electron microscopy (SEM) analysis and X-Ray diffraction (XRD) was conducted to determine particle sizes and their mineral composition. Area and personal respiratory exposure monitoring of particles not otherwise classified (PNOC), crystalline silica (quartz), PAH’s and VOC’s was conducted for the duration of each process to determine concentration levels for comparison with national legislation. Results and discussion: For new sand, a mean particle size of 137.49 μm at Facility A and 282.70 μm at Facility B was found, indicating that both Facilities had particle sizes larger than the inhalable size fraction. However, 10% of particles at Facility A were smaller than 75.35 μm, indicating the presence of inhalable particles. The SEM imaging supported the abovementioned particle size findings, with particle sizes > 100 μm. XRD analysis indicated that sand at Facility A had a majority percentage of mullite present while sand at Facility B comprised of 100% crystalline silica (quartz). Respirable PNOC exposure was lower than the national occupational exposure limits (OEL) at both facilities. Respirable silica (quartz) time-weighted average (TWA) exposure at Facility B indicated a 0.06 mg/m3 and 0.05 mg/m3 for two operators respectively, which is below the South African OEL-CL of 0.1 mg/m3 but at a concentration warranting further action. The only PAH compound present at either Facility was naphthalene, but with a TWA far below its OEL. Exposure to seven VOC’s (acetone, pentane, hexane, benzene, toluene, cyclohexane and naphthas) indicated TWA’s below their respective OEL’s at both facilities. Conclusions: This is the first study of its kind to assess the physicochemical characteristics and the respiratory exposure to HCS’s during the AM of sand casting moulds. This study is of imperative value, especially as the results have indicated exposure to respirable fractions of crystalline silica (quartz) at one Facility as well as low concentrations of naphthalene and other VOC’s, indicating the need for biological monitoring. This study opens the doors to research other facets of exposure, such as assessing the inhalable and thoracic exposure and assessing furfuryl alcohol exposure. Keywords: Silica, particle size fractions, occupational exposure, polycyclic aromatic hydrocarbons, volatile organic compounds, health effects, additive manufacturing
Agtergrond: Tydens dunlaagvervaardiging (DV) van sandgietsels word potensiële stof spesies van onbekende partikel groottes of mineraalsamestelling, en gevaarlike chemiese substanse (GCS’s) soos kristallyne silika, polisikliese aromatiese koolwaterstowwe (PAK) en vlugtige organiese verbindings (VOV) bevry/vrygestel tydens die voor-verwerking, verwerking en na-verwerking fases van vervaardiging. Doelwitte: Grootmaat sandmonsters is versamel van twee navorsingsfasiliteite (Fasiliteit A en Fasiliteit B) in Suid-Afrika om partikel groottes en mineraalsamestelling te bepaal. Respiratoriese blootstellingsmonitering van GCS is uitgevoer. Metodes: Fisies-chemiese karakterisering van nuwe, gebruikte en gemengde grootmaat sandmonsters deur partikel grootte verspreiding (PGV) analise, skandeerelektronmikroskopie (SEM) analise en X-straaldiffraksie (XSD) is uitgevoer om partikel groottes en hul mineraal samestelling te bepaal. Area en persoonlike respiratoriese blootstellingsmonitering van partikels nie andersins klassifiseerbaar (PBAK), kristallyne silika (kwarts), PAK en VOV, is uitgevoer vir die duur van elke proses om konsentrasie vlakke te bepaal vir 'n vergelyking met die nasionale wetgewing. Resultate en bespreking: Vir nuwe sand, is 'n gemiddelde partikel grootte van 137.49 μm by Fasiliteit A en 282.70 μm by Fasiliteit B gevind, wat aandui dat beide fasiliteite partikel groottes groter as die inasembare grootte fraksie gehad het. Tien persent van die partikels by Fasiliteit A was egter kleiner as 75.35 μm, wat dui op die teenwoordigheid van inasembare partikels. Die SEM beelde ondersteun die bogenoemde partikelgrootte bevindings, met partikel groottes > 100 μm. XSD ontleding het aangedui dat sand by Fasiliteit A 'n meerderheid persentasie van “mullite” bevat het terwyl sand by Fasiliteit B uit 100% kristallyne silika (kwarts) bestaan het. Respireerbare PBAK blootstelling was laer as die nasionale beroepsblootstelling drempel (BBD) by beide fasiliteite. Tyd beswaarde gemiddeld (TBG) van respireerbare silika (kwarts) blootstelling by Fasiliteit B was 0.06 mg/m3 en 0.05 mg/m3 onderskuidelik vir twee operateurs, wat laer is as die Suid-Afrikaanse BBD van 0.1 mg/m3, maar by 'n konsentrasie wat verdere aksie regverdig. Die enigste PAK teenwoordig by enige van die Fasiliteite was naftaleen, maar met 'n TBG ver onder sy BBD. Blootstelling aan seve VOV (asetoon, pentaan, heksaan, benseen, tolueen, sikloheksaan en nafta) het aangedui dat die TBG onder hul onderskeie BBD was by beide fasiliteite. Gevolgtrekkings: Dit is die eerste studie van sy soort wat die fisies-chemiese eienskappe en die respiratoriese blootstelling aan GCS’s gedurende die DV van sandgietsels evalueer. Hierdie studie is van imperatiewe waarde, veral omdat die een Fasiliteit se resultate die teenwoordigheid van respireerbare deeltjies van kristallyne silika (kwarts) asook lae konsentrasies van naftaleen en ander VOV’s getoon het, dui dit op die noodsaaklikheid vir biologiese monitering. Hierdie studie maak die deure oop om ander fasette van blootstelling, soos die assessering van die inasembare en torakale blootstelling en die assessering van furfural alkohol blootstelling. | en_US |
