Exposure to methylhexahydrophthalic anhydride (MHHPA) in two workplaces of the electric industry

Abstract

Methylhexahydrophthalic anhydride (MHHPA) is a hardener for hot-cured epoxy resins employed as insulators in the electric industry. MHHPA has only been measured as an ingredient with other alicyclic anhydrides, albeit there are also large processes which use only MHHPA. We collected MHHPA vapour in a set of devices: Teflon^® filter, glass spiral, TenaxTA^® tube connected consecutively together. Elution was performed with a solvent mixture of methyl-tert-butyl ether (70%), acetonitrile (30%), and acetic anhydride (0.5%). By capillary GC-ECD, the regression was linear (0.9994) in the practical low concentration range of 0.04–1 µg ml⁻¹ being equal to 0.001–0.035 mg m⁻³ in 30 l of air. The exposure was measured in two factories manufacturing electric appliances. The assembled objects were first impregnated with a liquid epoxy/hardener mixture, and then the resin hardened at elevated temperature. In condenser manufacturing, the operators' 8 h exposure ranged from 0.068 to 0.118 mg m⁻³, and the short-term exposure was during operation at ovens mean 1.90 mg m⁻³. The impregnation of coiled resistors and transfer of them to ovens caused the worst exposures, short-term mean 3.846 mg m⁻³ and long-term mean 2.191 mg m⁻³. During the ‘baking’, the ovens were closed and evacuated, but when the hot objects were moved out of the ovens, they continued during chilling to emit MHHPA, mean 0.366 mg m⁻³. In the adjacent areas, assembling, control rooms, offices, the exposure was still significant, 0.017–0.043 mg m³, due to leaks from the high exposure areas. Mechanical general ventilation and local exhausts were functioning. Respirators were available for short supervising of the hot equipment.