Hot dip galvanising is a method that prevents corrosion by a metallurgical bond between zinc and steel. In this industrial process, cooling and passivation baths of galvanised steel may use hexavalent chromium compounds. Cr(VI) is classified by the International Agency for Research on Cancer as Group 1 – carcinogenic to humans – and its use is restricted in most developed countries. Despite its toxicity, brazilian regulations still allow this hazardous chemical use. Thus, the development of effective control and protection rely on the understanding of occupational risks, as this paper proposes.Method
This is a descriptive quantitative cross-section case report of an industrial process: the passivation stage of galvanization. Brazilian labour inspection assigned a prohibition notice of the passivation as it was conducted, since any measures of occupational hygiene had been taken into account. Its participatory action procedure ends up preventing uncontrolled occupational exposure to Cr(VI). Secondary data source as official reports, notifications, chemical process protocols and registers from October/2016 to June/2017 have been analised.Results
Before the administrative prohibition, Cr(VI) concentration in the cooling tank was 5%; it has been eliminated. Passivation tank used to operate with 11% of Cr(VI) at 50°C; a trial is still ongoing to adjust the concentration. The company was authorised to perform tests from 0002 to 5% at 40°C. In this meanwhile, a satisfactory quality of galvanization was reached with a reduction of 98,84% in concentration. A ventilation system was designed to attend occupational hygiene requisites and the respiratory individual protection is effective for Cr(VI) manipulation.Conclusion
Attending the hierarchy of prevention and control measures, strategies to minimise hazards were developed, as follows: volatilisation reduction due to process, temperature and concentration modifications; ventilation system and changes in respiratory protection practices. The replacement of Cr(VI) is currently under study.