Survey of stray fields to which high frequency welder operators are exposed in the New Zealand plastics industry

During the mid 1980s the National Radiation Laboratory conducted a survey of radiofrequency dielectric welders used to manufacture plastic goods within New Zealand. The survey included measurements of stray electric and magnetic fields at 104 operator positions of 93 machines. Measured levels were compared with guideline limits recommended by health authorities overseas for persons exposed during the course of their occupations. Results showed that 44% of operators were subjected to above limit levels, to at least one part of the body. In 6% of cases the excess was by more than a factor of 10 and the rates of exposure were comparable to recognized thermal hazard thresholds. This situation is considered unsatisfactory from a health protection viewpoint. However, there are recognized difficulties in assessing exposure in the vicinity of welders and application of a recent exposure standard which more specifically takes account of these difficulties indicates a somewhat lower level of above limit exposure situations. It is uncertain whether or not exposure to the higher levels of fields might lead to ill health. There was no evidence of acute, short term injury due to the fields alone, although several operators and factory managers described cases of severe burns after touching welder electrodes. It is recommended that the highest exposure machines in use should be identified and progressively removed from use. (author). 9 refs., 9 tabs., 4 figs., 9 ills