Evaluation of the OSHA 42 and NIOSH 5521 methods in determining the free isocyanate concentration in aerosols and vapor phases during application of two component 1,6-hexamethylene diisocyanate paints
Abstract
When sampling for isocyanates, the two currently recommended methods (OSHA 42 and NIOSH 5521) have limitations that cause under estimation of the isocyanate concentration reported. During spray painting operations, isocyanate is present in both aerosol and vapor forms. When the NIOSH method is used the midget impinger inlet and outlet nozzles tend to plug as paint particles collect there during sampling. As the outlet nozzle opening becomes smaller, the velocity of the sampling stream increases causing particles to pass through the derivatizing agent without capture. Both phenomena result in underestimation of aerosol content of the sampled air. In the OSHA method, particles adhere to the surface of the glass fiber filter as seen in Scanning Electron Microscope photographs. The presence of these particles reduce the effectiveness of solid sampling media such as glass fiber filters in sampling for aerosol isocyanates since only limited contact between the derivatizing agent and the aerosol particles collected on the filter surface occurs. Once the outer surface of the isocyanate particle is polymerized, the derivatizing agent cannot break the bonds in order to form urea. When sampling for vapors, the OSHA and NIOSH methods are equally effective. Using a Fourier Transform Infrared Spectrometer reaction rates between isocyanates and the derivatizing agent for the OSHA method were studied. Although usually considered instantaneous, this study showed that these reactions took as long as several hours to go to completion. During this time isocyanate evaporation into the air flow is occurring. In both methods, as much as five percent of the isocyanates are lost due to slow reactions and/or sampling media break through.
Description
Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.
Includes bibliographical references.
Includes bibliographical references.
Keywords
industrial hygiene., Major industrial hygiene.