Reducing exposure levels of immersion washing workers to ortho-phthalaldehyde by improving exhaust systems

The American Conference of Governmental Industrial Hygienists recommends a threshold limit value-ceiling (TLV-C) of 0.1 ppb for occupational exposure to ortho-phthalaldehyde (OPA) used in washing endoscope probes. To adhere to this extremely low exposure limit, this case study aimed to reduce OPA exposure concentrations of workers during immersion washing of an endoscope probe body. This was achieved by attaching a new duct and hood to the existing ceiling exhaust system.

The type of hood was determined by calculating and comparing the capture velocity obtained by assuming either an exterior or an enclosing hood. Additionally, the effect on improving the working environment was tested before and after the installation of the hood by measuring the OPA vapor concentration.

The calculated capture velocities of the exterior and enclosing hoods were 0.05 m/s and 0.19 m/s, respectively. Considering the operability, the exterior hood was more appropriate; however, the calculated capture velocity indicated potential inadequacy in meeting the TLV-C requirement, leading to the adoption of the enclosing hood. The OPA vapor concentration in ceiling value measurements taken after the enclosing hood was fitted was reduced to 0.2 ppb, that is, 1/10 of the original concentration.

Although the environmental concentration after the improvement still exceeded the TLV-C of 0.1 ppb, this study's findings indicate that even substances with extremely low occupational exposure limits can be managed with appropriate local exhaust ventilation.