The Surface Tension of Synthetic Blood used for ASTM F1670 Penetration Tests

The American Society for Testing and Material (ASTM International) F1670 test method was based on research involving transmission of bloodborne pathogens (Hepatitis B, Hepatitis C, and HIV) in the 1980s. The test method details the measurement of synthetic blood penetration through garments. A key parameter affecting penetration is synthetic blood surface tension which is measured via du Noüy ring tensiometer. However, little is known about the sources of variation impacting surface tension measurements. In this study, the synthetic blood used for ASTM F1670 was evaluated from within the ASTM F903 test apparatus and with two mixing treatments. Measurements were compared against two outside laboratories and with two alternate tensiometric methods (pendant drop and capillary rise). It was found that using the methods specified in the ASTM F1670 test method, surface tension of the synthetic blood was not 40-44 dynes/cm as was expected. The surface tension was initially above 50 dynes/cm and declined to below 40 dynes/cm after 60 minutes. The surface tension within the penetration cell was relatively constant over time, showing that the surface tension measurements outside the penetration cell are not indicative of the surface tension within the apparatus during the test. Shaking the synthetic blood, a mixing procedure detailed in the ASTM F1670 test method, increased the surface tension. The increase was greatest in a container having more airspace. Du Noüy ring measurements by NIOSH compared to external labs were within 15%. Testing with alternate methods showed that the "open-to-atmosphere" methods (ring and drop) began lower and declined rapidly when compared to the "closed-to-atmosphere" method (capillary). Results of this research will help amend the ASTM F1670 standard to better characterize the measurement and handling of synthetic blood used in the ASTM F1670 test and to provide a framework for consideration of test fluid used in future ASTM standards.